Protective Device Coordination Study

Revision 6 · Oct 19, 2026 +733 −735

SynC Standards Team — Specifier (Platform Standards) ✓ OfficialDiscloses employment SynC (SynC Platform Team)

Remake batch 25 and its neighbor re-points, batch 24 where missing, and the adopted-electrical-code parameter: brought in line with the authoring repository

Showing changes from Rev 5 to Rev 6 in Protective Device Coordination Study.

−---

−title: Protective Device Coordination Study

−category: Electrical / Power Studies

−toc_depth: 3

−description: >

− When to use: A time-current coordination study for low- and medium-voltage power distribution systems rated 38 kV and below, where multiple overcurrent protective devices are installed in series and selective operation is required. Covers the analysis, settings recommendations, and deliverables that demonstrate the closest upstream protective device to a fault opens first, leaving the rest of the system energized. Includes coordination of relays, low-voltage power circuit breakers, molded-case and insulated-case breakers, fuses, and motor starter overload elements; coordination with transformer through-fault damage curves, conductor damage curves, and motor starting and inrush envelopes; and the dedicated selective-coordination requirements of NEC 700.27 and 701.27 for emergency and legally required standby systems.

− Not intended for: The short-circuit study itself (see [[sync/short-circuit-study]], which is the mandatory predecessor); arc-flash incident-energy calculations (see [[sync/arc-flash-study]], which is run after coordination is finalized); load-flow, harmonic, motor-starting transient, or transient-stability studies; the protective relaying scheme design itself (relay element selection and one-line single-function block design); and utility-side coordination beyond the point of common coupling.

−---

−

−# Scope {toc}

−

−## This specification covers the preparation, documentation, and acceptance of a protective device coordination study for the project's electrical distribution system. {note}

−

−## The study shall demonstrate, by time-current curve analysis, that the overcurrent protective devices installed in the system operate selectively over the full range of available fault currents and overload conditions.

−

−## Selective operation means the device immediately upstream of a fault opens first and the remainder of the system stays energized.

−

−## A coordination study is the middle study in a three-study sequence: the short-circuit study establishes available fault current at every bus, the coordination study uses those values to set protective devices selectively, and the arc-flash study then calculates incident energy at those settings. {note}

−

−## The Contractor shall not begin the coordination study until the short-circuit study is complete and accepted. See [[sync/short-circuit-study]].

−

−## The Contractor shall not begin the arc-flash study until the coordination study is complete and accepted. See [[sync/arc-flash-study]].

−

−## This standard shall apply from the project's point of common coupling with the serving utility through every downstream overcurrent protective device on the project, including service equipment, distribution switchgear and switchboards, panelboards, motor control centers, dry-type and pad-mount transformers serving the project, on-site generators and uninterruptible power supplies, and the protective devices ahead of utilization equipment where required for selective coordination.

−

−## Coordination with the utility's protective devices shall be included only to the extent that the utility's settings are available and that coordination at the service entrance is required by the project documents or by the utility.

−

−## This standard does not cover the design of the protective relaying scheme; the selection of relay functions, the choice of CT ratios, and the architecture of differential and pilot schemes are engineered upstream of the study by the Engineer of Record. {note}

−

−## The study shall use the as-designed protective relaying scheme and produce settings for it.

−

−# Referenced Standards {toc}

−

−## Equipment, calculations, and study methodology shall comply with the latest adopted edition of the following standards and codes.

−

−## Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

−

−## Applicable Standards and Codes {toc}

−

−| Standard | Title |

−|----------|-------|

−| NFPA 70 | National Electrical Code (Articles 240, 430, 450, 517, 695, 700, 701, 702, 708) |

−| NFPA 70E | Standard for Electrical Safety in the Workplace |

−| NFPA 110 | Standard for Emergency and Standby Power Systems |

−| IEEE 242 | Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems (Buff Book) |

−| IEEE 399 | Recommended Practice for Industrial and Commercial Power Systems Analysis (Brown Book) |

−| IEEE 551 | Recommended Practice for Calculating Short-Circuit Currents in Industrial and Commercial Power Systems (Violet Book) |

−| IEEE 1015 | Recommended Practice for Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems (Blue Book) |

−| IEEE C37.13 | Low-Voltage AC Power Circuit Breakers Used in Enclosures |

−| IEEE C37.90 | Relays and Relay Systems Associated with Electric Power Apparatus |

−| IEEE C37.91 | Guide for Protecting Power Transformers |

−| IEEE C37.96 | Guide for AC Motor Protection |

−| IEEE C57.12.00 | General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers |

−| IEEE C57.109 | Guide for Liquid-Immersed Transformers Through-Fault-Current Duration |

−| IEEE C57.12.59 | Guide for Dry-Type Transformer Through-Fault Current Duration |

−| ICEA P-32-382 | Short-Circuit Characteristics of Insulated Cable |

−| ICEA P-45-482 | Short-Circuit Performance of Metallic Shields and Sheaths on Insulated Cable |

−| ANSI/NETA ATS | Acceptance Testing Specifications for Electrical Power Equipment and Systems |

−| ANSI/NETA ETT | Standard for Certification of Electrical Testing Technicians |

−| UL 489 | Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures |

−| UL 1066 | Low-Voltage AC and DC Power Circuit Breakers Used in Enclosures |

−

−# Submittals {toc}

−

−## Action Submittals {toc}

−

−### Contractor shall submit the following for the Engineer's review and acceptance:

−

−- Study report, sealed by a Professional Engineer licensed in the project jurisdiction, organized as described in [Deliverables](#deliverables) below

−- Software model file used to produce the study, in the native format of the software identified in the study, available to the Engineer of Record on request

−- Time-current curve (TCC) plots covering every coordination pair in the system, in PDF and in the source format of the study software

−- A consolidated settings table listing every adjustable device, every adjustment, the recommended setting, and any field-set or factory-set status

−- A list of any coordination compromises required by the system and the basis for accepting each compromise

−- A list of any equipment changes (frame size changes, fuse class changes, trip-unit replacements) required to achieve coordination, with cost and schedule impact identified

−

−```datasheet

−label: Action Submittals Required

−type: checkbox

−options:

− - "PE-sealed study report"

− - "Software model file (native format)"

− - "TCC plots (PDF + source)"

− - "Consolidated device settings table"

− - "List of coordination compromises with justifications"

− - "List of required equipment changes"

− - "Settings sheets formatted for relay technicians"

−default: "PE-sealed study report"

−```

−

−### Field commissioning of relay and breaker settings shall not proceed until the coordination study is accepted in writing.

−

−## Closeout Submittals {toc}

−

−### Contractor shall provide the following at substantial completion, after field commissioning of the protective devices:

−

−- As-set settings table, recording the actual setting applied to each device in the field, signed by the commissioning technician

−- Settings verification test reports per [[sync/electrical-acceptance-testing]] showing that each adjustable device trips at its recommended pickup and within the recommended time delay

−- An updated TCC plot package reflecting any settings deviations made during commissioning, with each deviation justified

−- A written re-study trigger list (see [Re-Study Triggers](#re-study-triggers) below) issued to the Owner for inclusion in the facility's electrical operating procedures

−

−```datasheet

−label: Closeout Submittals Required

−type: checkbox

−options:

− - "As-set settings table signed by commissioning technician"

− - "Settings verification test reports"

− - "Updated TCC plot package with justified deviations"

− - "Written re-study trigger list issued to Owner"

−default: [As-set settings table signed by commissioning technician, Settings verification test reports, Updated TCC plot package with justified deviations, Written re-study trigger list issued to Owner]

−```

−

−# Quality Assurance {toc}

−

−## Engineer of Record for the Study {toc}

−

−### The coordination study shall be performed by, or under the direct supervision of, a Professional Engineer licensed in the project jurisdiction and experienced in the protection and coordination of power systems of the type, voltage, and size of the project's system.

−

−### The study report shall bear the seal and original signature of that engineer.

−

−### Study Engineer Qualification {toc}

−

−```datasheet

−label: Study Engineer Qualification

−type: select

−options:

− - "PE licensed in project jurisdiction, electrical discipline"

− - "PE plus NETA Level III or IV technician oversight"

− - "PE plus NICET Level III or IV electrical power testing certification"

−default: "PE licensed in project jurisdiction, electrical discipline"

−```

−

−## Study Software {toc}

−

−### The study shall be performed in commercial power-systems analysis software that maintains a current library of low-voltage breaker trip curves, fuse curves, relay characteristics, and motor data, and that produces TCC plots on logarithmic axes.

−

−### Hand-drawn or general-purpose-plotting-software TCC curves shall not be acceptable for the action submittal because they cannot be verified against published device characteristics.

−

−### The software's device library shall be at a release current within twelve months of the study date.

−

−### The study report shall identify the software name, version, and device-library revision so that the model can be reopened and re-evaluated during the system's life.

−

−### Study Software Selection {toc}

−

−```datasheet

−label: Study Software

−type: select

−options:

− - "Commercial power-systems analysis software with maintained device library"

− - "Owner-specified software (project-specific)"

−default: "Commercial power-systems analysis software with maintained device library"

−```

−

−## Independence {toc}

−

−### Where the contract documents specify an independent coordination study, the study engineer shall not be employed by, contracted to, or financially associated with the manufacturer of the protective devices being studied.

−

−### An independent study is recommended for projects with multiple equipment manufacturers, for healthcare and other life-safety-critical facilities, and where the Owner requires unbiased settings recommendations. {note}

−

−### Study Independence Selection {toc}

−

−```datasheet

−label: Study Independence

−type: radio

−options:

− - "Independent — engineer not affiliated with equipment manufacturer"

− - "Manufacturer-performed — included with equipment supply"

−default: "Independent — engineer not affiliated with equipment manufacturer"

−```

−

−# Coordination Criteria {toc}

−

−## The coordination criteria are the rules the study uses to decide whether two devices in series coordinate. {note}

−

−## These criteria shall be stated in the study report so that the basis for every conclusion is auditable.

−

−## Coordination Time Interval {toc}

−

−### Selective coordination is demonstrated by maintaining a minimum time interval between the operating curve of any downstream device and the operating curve of any upstream device, over the range of fault currents at which both devices respond. {note}

−

−### The minimum coordination time interval (CTI) shall account for the upstream device's breaker interrupting time, the downstream device's overshoot or memory error, and a safety margin.

−

−### CTI Setpoints {toc}

−

−```datasheet

−label: Minimum CTI — Electromechanical Relays Upstream

−type: range

−unit: seconds

−options:

− min: 0.25

− max: 0.50

− setpoints: [0.25, 0.3, 0.35, 0.4, 0.5]

−default: 0.40

−```

−

−```datasheet

−label: Minimum CTI — Microprocessor (Static) Relays Upstream

−type: range

−unit: seconds

−options:

− min: 0.15

− max: 0.40

− setpoints: [0.15, 0.2, 0.25, 0.3, 0.4]

−default: 0.30

−```

−

−```datasheet

−label: Minimum CTI — Low-Voltage Breaker to Low-Voltage Breaker

−type: range

−unit: seconds

−options:

− min: 0.06

− max: 0.30

− setpoints: [0.06, 0.1, 0.15, 0.2, 0.3]

−default: 0.10

−```

−

−### The IEEE 242 guidance is that electromechanical relays require approximately 0.3 to 0.4 seconds between curves, and microprocessor relays require approximately 0.2 to 0.3 seconds; low-voltage power circuit breakers with short-time delay coordinate on a tighter interval because their internal clocks are deterministic. {note}

−

−### The CTI shall be measured at the minimum point of separation between curves, not over the full curve length.

−

−### Brief intersections at currents that are not credible at the bus in question shall not be treated as coordination failures, but shall be identified in the study report as discussed in [Coordination Compromises](#coordination-compromises) below.

−

−## Selectivity Type {toc}

−

−```datasheet

−label: Selectivity Requirement — General Distribution

−type: radio

−options:

− - "Full selective coordination at all fault currents up to the available short-circuit current"

− - "Partial selectivity — selective up to the published manufacturer let-through value"

− - "Time-based selectivity only — selective above the instantaneous knee"

−default: "Full selective coordination at all fault currents up to the available short-circuit current"

−```

−

−### Full selective coordination ensures that the downstream device clears every fault, including bolted faults, before the upstream device unlatches. {note}

−

−### Partial selectivity shall be acceptable for general distribution only where the Engineer documents the consequence of a non-selective trip at the bus in question.

−

−### Time-based selectivity, in which devices coordinate only above the upstream device's instantaneous pickup, shall be acceptable only where the downstream device's instantaneous region does not overlap any current the downstream device will see in service.

−

−### For the emergency and legally required standby branches addressed in [Selective Coordination for Life Safety](#selective-coordination-for-life-safety) below, full selective coordination is required by code and shall not be reduced.

−

−## Instantaneous Override and Energy Reduction {toc}

−

−### The selective-coordination requirement shall not exempt a breaker from the arc energy reduction requirements of NEC 240.87 (for circuit breakers rated or adjustable to 1200 A or higher) or 240.67 (for fuses of equivalent rating).

−

−### Where an energy-reducing method is employed, the study shall demonstrate that the method does not compromise selective coordination outside of its activation window.

−

−### For an energy-reducing maintenance switch, the activation window is the period during which the switch is in the maintenance position. {note}

−

−### Arc Energy Reduction Approach {toc}

−

−```datasheet

−label: Arc Energy Reduction Coordination Approach

−type: select

−options:

− - "Zone-selective interlocking (ZSI) — no degradation to coordination"

− - "Energy-reducing maintenance switch (ARMS) — coordination evaluated in normal mode only"

− - "Differential relaying — coordination preserved by selectivity of the differential zone"

− - "Instantaneous trip set below available arcing current — coordination evaluated as set"

− - "Energy-reducing active arc-flash mitigation — coordination evaluated in normal mode only"

−default: "Zone-selective interlocking (ZSI) — no degradation to coordination"

−```

−

−### Zone-selective interlocking is the preferred method on systems where selective coordination is required because it reduces upstream clearing time only when no downstream device sees the fault, so coordination is preserved by the interlock signal itself. {note}

−

−### Where energy-reducing maintenance switches are used, the study shall evaluate coordination in the normal (non-maintenance) state.

−

−### The ARMS-active state intentionally sacrifices coordination to limit incident energy and is acceptable for that purpose. {note}

−

−### Temporary adjustment of the instantaneous trip setting to achieve arc energy reduction is not permitted by NEC 240.87(B), and the study shall not recommend it.

−

−# Input Data Requirements {toc}

−

−## The coordination study cannot proceed without complete and verified input data. {note}

−

−## The Contractor shall not submit a coordination study until every input listed below is in hand.

−

−## Assumed or placeholder values shall be flagged in the report and corrected before acceptance.

−

−## Short-Circuit Study Results {toc}

−

−### The accepted short-circuit study per [[sync/short-circuit-study]] shall be used as the source of the available short-circuit current at every bus in the system.

−

−### The coordination study shall use the same software model — or a model verified against the same one-line, equipment data, and impedance values — as the short-circuit study so that the two analyses produce consistent fault currents.

−

−### Short-Circuit Study Status {toc}

−

−```datasheet

−label: Short-Circuit Study Status

−type: radio

−options:

− - "Accepted by Engineer of Record — used as input to this study"

− - "Submitted but not yet accepted — coordination study held pending acceptance"

− - "Not yet performed — coordination study not started"

−default: "Accepted by Engineer of Record — used as input to this study"

−```

−

−## Utility Source Data {toc}

−

−### The serving utility's available short-circuit contribution, X/R ratio at the point of common coupling, and the time-current characteristics of the utility's protective device(s) immediately upstream of the project shall be obtained in writing from the utility.

−

−### Where the utility declines to provide its protective device curves, the study shall document the request and the response, and coordination at the service entrance shall be limited to the available information.

−

−## Equipment Nameplate and Curve Data {toc}

−

−### The required equipment data includes the following: {note}

−

−- Transformer kVA, primary and secondary voltages, percent impedance, X/R, vector group, and category for through-fault analysis per IEEE C57.109 or C57.12.59

−- Motor nameplate horsepower, full-load amps, locked-rotor amps, locked-rotor time, code letter, and starting method for every motor 50 hp and larger; smaller motors shall be modeled in aggregate at each bus

−- Cable type, conductor material, insulation type, size, and length for every feeder, for conductor damage curve plotting per ICEA P-32-382

−- Generator nameplate kW/kVA, subtransient and transient reactances, decrement curve, and the operating characteristics of the generator overcurrent device

−- Relay model and firmware, CT ratios, and CT accuracy class

−- Breaker frame size, trip unit model and rating plug, and adjustable function range

−

−### The study shall use the actual nameplate and curve data of the equipment installed on the project, not generic or assumed values.

−

−```datasheet

−label: Equipment Data Source

−type: radio

−options:

− - "As-built nameplate data verified at equipment"

− - "Manufacturer-confirmed shop submittal data"

− - "Specification or schedule data (verify before commissioning)"

−default: "Manufacturer-confirmed shop submittal data"

−```

−

−### Coordination based on specification data shall be acceptable for the action submittal so that ordering and installation are not delayed.

−

−### The study shall be updated against as-built nameplate data before commissioning.

−

−### A coordination study performed on imagined or rounded equipment data is not a coordination study. {note}

−

−## One-Line Diagram {toc}

−

−### A single-line diagram showing the complete system from the utility source through every overcurrent device covered by the study shall be provided in the report.

−

−### The one-line shall identify each device by its project tag, frame size, trip rating, and the bus to which it is connected, and shall show available short-circuit current at every bus.

−

−### One-line and protection diagram are [[drawing: per the project electrical drawings, marked up to reflect the as-modeled system]].

−

−# Coordination Analysis {toc}

−

−## The coordination analysis is the work of selecting a setting for every adjustable device such that the criteria in [Coordination Criteria](#coordination-criteria) are met. {note}

−

−## The study shall analyze, at minimum, the coordination pairs listed in [Coordination Pairs Analyzed](#coordination-pairs-analyzed) below.

−

−## Coordination Pairs Analyzed {toc}

−

−```datasheet

−label: Coordination Pairs Included in Study

−type: checkbox

−options:

− - "Utility protective device to project main"

− - "Project main to each feeder"

− - "Each feeder to its downstream distribution device"

− - "Distribution device to each branch device"

− - "Branch device to motor starter (where applicable)"

− - "Branch device to fuse / fused disconnect (where applicable)"

− - "Generator overcurrent device to downstream distribution"

− - "UPS bypass overcurrent device to downstream distribution"

− - "Transfer switch upstream and downstream devices (emergency / standby)"

−default: "Utility protective device to project main"

−```

−

−### Each pair shall be plotted on a single TCC sheet showing both devices' curves, the relevant damage curves and equipment envelopes, the available short-circuit current at the downstream device's load terminals, and the available short-circuit current at the upstream device's load terminals where different.

−

−## Transformer Damage Curves {toc}

−

−### For every transformer in the system, the through-fault damage curve per IEEE C57.109 (liquid-filled) or C57.12.59 (dry-type) shall be plotted on the TCC sheet showing the transformer's primary and secondary overcurrent devices.

−

−### The primary protective device shall clear a secondary-side bolted fault before the through-fault curve is reached.

−

−### The through-fault clearing requirement is a coordination requirement with equipment, not a coordination requirement between two devices, but it shall be demonstrated on the same plot. {note}

−

−### Transformer Category for Through-Fault Curve {toc}

−

−```datasheet

−label: Transformer Category for Through-Fault Curve

−type: select

−options:

− - "Auto-select per kVA and IEEE C57.109"

− - "Category I (5–500 kVA single-phase / 15–500 kVA three-phase)"

− - "Category II (501–1667 kVA single-phase / 501–5000 kVA three-phase)"

− - "Category III (1668–10000 kVA single-phase / 5001–25000 kVA three-phase)"

− - "Category IV (above Category III limits)"

−default: "Auto-select per kVA and IEEE C57.109"

−```

−

−### Transformer inrush (commonly modeled at 8 to 12 times full-load current for 0.1 seconds, with manufacturer data preferred where available) shall be plotted as a point or short curve on the primary side so that the primary protective device's curve is shown not to operate on inrush.

−

−### The IEEE C37.91 guidance on transformer overcurrent protection shall be applied to verify that fuse and relay selections sit below the damage curve and above the inrush point.

−

−## Motor Starting and Inrush {toc}

−

−### For every motor 50 hp and larger, the motor starting envelope (locked-rotor current for locked-rotor time, plus any reduced-voltage or soft-start profile if applicable) shall be plotted on the TCC sheet showing the motor branch overcurrent device.

−

−### The branch device's long-time pickup and curve shall be clear of the starting envelope.

−

−### The instantaneous shall be set above the locked-rotor current with margin sufficient to avoid nuisance trips on starting transients.

−

−### Motor overload elements (thermal or electronic) shall be plotted to demonstrate that the overload protects the motor's thermal damage curve.

−

−### Motor Starting Method Modeled {toc}

−

−```datasheet

−label: Motor Starting Method Modeled

−type: select

−options:

− - "Across-the-line (full-voltage start)"

− - "Reduced-voltage soft start (RVSS)"

− - "Variable-frequency drive (VFD)"

− - "Wye-delta or autotransformer"

−default: "Across-the-line (full-voltage start)"

−```

−

−### Motors below 50 hp shall be modeled in aggregate at their bus to capture their contribution to short-circuit current.

−

−### Individual coordination of small-motor branch circuits is generally not required unless specifically called for. {note}

−

−## Conductor Damage Curves {toc}

−

−### Cable damage curves per ICEA P-32-382 shall be plotted for every feeder where the cable's short-circuit withstand is a binding constraint on the upstream device's setting — typically every feeder of 1/0 AWG and larger and every conductor in series with an upstream device set to delay tripping.

−

−### The upstream device's curve shall clear the fault before the cable damage curve is reached, so that a fault at the far end of the feeder does not damage the cable insulation before the breaker interrupts.

−

−### Conductor Damage Curve Scope {toc}

−

−```datasheet

−label: Conductor Damage Curves Plotted For

−type: select

−options:

− - "All feeders 1/0 AWG and larger"

− - "All feeders to switchboards, MCCs, and large panelboards"

− - "Only where required by Engineer of Record (per-feeder direction)"

−default: "All feeders 1/0 AWG and larger"

−```

−

−### ICEA cable damage curves became part of mainstream coordination practice with the 2008 NEC revisions. {note}

−

−### ICEA cable damage curves shall be used in preference to manufacturer-specific curves except where the cable manufacturer publishes a more restrictive curve.

−

−## Ground-Fault Coordination {toc}

−

−### Where ground-fault protection is provided on multiple devices in series — most commonly on a service main of 1000 A or larger per NEC 230.95 and on downstream feeders — the ground-fault protective devices shall be coordinated independently of the phase coordination.

−

−### Ground-fault pickup and time delay shall be plotted on separate TCC sheets from the phase coordination, because the available ground-fault current and the relevant device curves differ from the phase case.

−

−### Ground-Fault Coordination Applicability {toc}

−

−```datasheet

−label: Ground-Fault Coordination Required

−type: radio

−options:

− - "Yes — ground-fault protection present on two or more series devices"

− - "No — ground-fault protection on service main only"

− - "Not applicable — no ground-fault protection on the system"

−default: "Yes — ground-fault protection present on two or more series devices"

−```

−

−### NEC 230.95(A) limits the maximum setting of the service-equipment ground-fault protective device to 1200 A pickup and 1 second time delay at 3000 A. {note}

−

−### Coordination of downstream ground-fault devices with the service main shall respect the NEC 230.95(A) ceiling.

−

−# Settings Recommendations {toc}

−

−## The study shall produce a specific recommended setting for every adjustable function of every device.

−

−## Recommendations of the form "set per manufacturer" or "factory defaults" shall not be acceptable for adjustable devices.

−

−## Low-Voltage Breaker Trip Unit Settings {toc}

−

−### For every low-voltage breaker with an electronic trip unit, the study shall recommend the following:

−

−- Long-time pickup (LTPU) — typically expressed as a multiple of the rating plug

−- Long-time delay (LTD) — at a specified reference current per the trip unit's curve family

−- Short-time pickup (STPU) — typically expressed as a multiple of the LTPU

−- Short-time delay (STD) — including I²t in/out selection where the trip unit supports it

−- Instantaneous pickup (INST) — or "off" / "maintenance" for selectively coordinated systems with separate arc energy reduction

−- Ground-fault pickup and delay (LSIG units), with I²t in/out where adjustable

−- Zone-selective interlocking (ZSI) participation — short-time, ground-fault, or both

−

−```datasheet

−label: Trip Unit Setting Format in Report

−type: radio

−options:

− - "Per-device settings sheet (one page per breaker)"

− - "Consolidated table (all breakers, one document)"

− - "Both per-device sheet and consolidated table"

−default: "Both per-device sheet and consolidated table"

−```

−

−### A per-device settings sheet is what the commissioning technician carries to the breaker, and the consolidated table is what the Engineer reviews for system-wide selectivity; producing both is recommended. {note}

−

−## Protective Relay Settings {toc}

−

−### For every microprocessor or electromechanical relay, the study shall recommend the setting for each enabled element.

−

−### For overcurrent elements the recommended setting shall include pickup, time dial, and curve type (very inverse, extremely inverse, IEEE moderately inverse, etc.).

−

−### For directional and differential elements the study shall recommend the relevant slope, pickup, and characteristic-angle settings.

−

−### Relay function numbers per IEEE C37.2 shall be used to identify each element.

−

−### Settings shall be presented in a format that can be entered directly into the relay's commissioning software without translation.

−

−## Fuse Selection {toc}

−

−### Where fuses are used, the study shall recommend the fuse class, ampere rating, and where applicable the interrupting rating necessary for the available fault current at the fuse location.

−

−### Where coordination requires a specific fuse manufacturer's curve family — for example, where a Class L time-delay fuse coordinates with a downstream Class J in a way that a fast-acting Class L would not — the study shall note that the curve family, not a specific manufacturer's catalog number, is the basis for coordination.

−

−## Motor Overload Elements {toc}

−

−### For thermal or electronic motor overload elements, the study shall recommend the trip class (NEMA Class 10, 20, or 30) and the pickup current setting.

−

−### Trip class shall be selected to protect the motor without nuisance-tripping on the motor's acceleration time.

−

−### Motor Overload Trip Class {toc}

−

−```datasheet

−label: Motor Overload Trip Class Default

−type: select

−options:

− - "Class 10 (standard, acceleration time below 10 s)"

− - "Class 20 (long acceleration, high-inertia loads)"

− - "Class 30 (very long acceleration, mining/grinding-type loads)"

−default: "Class 10 (standard, acceleration time below 10 s)"

−```

−

−## Coordination Compromises {toc}

−

−### A real system frequently contains a coordination pair that does not coordinate at every credible fault current. {note}

−### The study shall not pretend otherwise.

−### Common compromises include the following: {note}

−

−- An upstream main with an instantaneous element that overlaps the downstream feeder above a certain fault current, accepted because the available fault current at the feeder is below the overlap.

−- A series-rated combination of an upstream breaker and a downstream breaker that is listed by the manufacturer but is not selectively coordinated; the listing is a fault-withstand listing, not a selectivity listing.

−- A current-limiting fuse and an upstream breaker whose let-through coordinate above the fuse's current-limiting threshold but not below; selectivity is achieved on bolted faults but not on lower-current faults.

−

−### Each compromise shall be identified, the fault-current range over which the compromise occurs shall be stated, the consequence of a non-selective trip shall be described, and the Engineer of Record's acceptance of the compromise shall be obtained in writing.

−

−### Compromises shall not be applied to circuits required by code to be selectively coordinated (see [Selective Coordination for Life Safety](#selective-coordination-for-life-safety)) without a code variance from the Authority Having Jurisdiction.

−

−# Selective Coordination for Life Safety {toc}

−

−## NEC 700.27 — Emergency Systems {toc}

−

−### Overcurrent devices in the emergency system distribution shall be selectively coordinated with all supply-side overcurrent protective devices per NEC 700.27.

−

−### Selective coordination means that the device immediately upstream of a fault opens before any further upstream device, at all available fault currents and at all overload currents, including at the instantaneous region of the curves. {note}

−

−### Partial coordination, time-based coordination above a current threshold, and series-rated combinations that do not maintain selectivity shall not be acceptable for the emergency branch.

−

−### Emergency System Present {toc}

−

−```datasheet

−label: Emergency System Present on Project

−type: radio

−options:

− - "Yes — Article 700 emergency system included"

− - "No"

−default: "No"

−```

−

−### Where an emergency system is present, the study shall include a dedicated section that demonstrates selective coordination from the emergency source (generator, central inverter, or other) through every device on the emergency branch.

−

−### The 2023 NEC clarified, in 700.32, that selective coordination shall be examined both upstream and downstream of any device that is replaced or modified during the life of the system; this re-evaluation obligation shall be communicated to the Owner in the re-study trigger list.

−

−## NEC 701.27 — Legally Required Standby Systems {toc}

−

−### Overcurrent devices for the legally required standby system shall be selectively coordinated with all supply-side overcurrent protective devices per NEC 701.27.

−

−### The selective-coordination requirement, including the upstream-and-downstream re-evaluation obligation added to 701.32 in the 2023 NEC, shall apply to the legally required standby branch in the same manner as to the emergency branch.

−

−### Legally Required Standby System Present {toc}

−

−```datasheet

−label: Legally Required Standby System Present on Project

−type: radio

−options:

− - "Yes — Article 701 legally required standby system included"

− - "No"

−default: "No"

−```

−

−## NEC 708 — Critical Operations Power Systems {toc}

−

−### Where the project includes a Critical Operations Power System (COPS) per NEC Article 708, the dedicated selective coordination requirements of 708.54 shall apply.

−

−### COPS is most commonly identified for designated critical-operations data centers, water and wastewater facilities, and certain government facilities. {note}

−

−### Critical Operations Power System Present {toc}

−

−```datasheet

−label: Critical Operations Power System (NEC 708) Present

−type: radio

−options:

− - "Yes"

− - "No"

−default: "No"

−```

−

−## Healthcare Essential Electrical Systems {toc}

−

−### For healthcare facilities the essential electrical system per NFPA 99 and NEC Article 517 imposes additional reliability and selective-coordination considerations. {note}

−

−### Where the project includes a healthcare essential electrical system, coordination shall additionally satisfy NFPA 99 and the requirements of [[sync/healthcare-essential-electrical-systems]].

−

−### Healthcare Essential Electrical System Present {toc}

−

−```datasheet

−label: Healthcare Essential Electrical System Present

−type: radio

−options:

− - "Yes — coordinate with healthcare standard"

− - "No"

−default: "No"

−```

−

−## Fire Pump Circuits {toc}

−

−### Fire pump circuits per NEC Article 695 shall be served such that the fire pump runs without interruption short of mechanical failure of the pump itself.

−

−### The fire pump's individual overcurrent device shall be sized to carry locked-rotor current indefinitely per 695.4(B)(2)(a), which produces a curve that intentionally does not coordinate with anything downstream and is not expected to.

−

−### The study shall plot the fire pump device's curve and shall demonstrate that the upstream service device coordinates with the fire pump device for non-fire-pump faults.

−

−# Deliverables {toc}

−

−## The study report shall be organized so that the Engineer of Record, the commissioning technician, and the Owner's maintenance staff can each find what they need without reading the entire report.

−

−## Report Organization {toc}

−

−```datasheet

−label: Study Report Sections (Minimum)

−type: checkbox

−options:

− - "Executive summary and conclusions"

− - "Study methodology and software identification"

− - "System one-line diagram with device tags and fault currents"

− - "Input data summary (equipment, cable, motor, source)"

− - "Coordination criteria stated explicitly"

− - "TCC plots for every coordination pair"

− - "Consolidated settings table"

− - "Per-device settings sheets for field use"

− - "Coordination compromises with justifications and EOR acceptance"

− - "Selective coordination demonstration for emergency / standby branches"

− - "Re-study trigger list"

− - "PE seal and signature"

−default: "Executive summary and conclusions"

−```

−

−## TCC Plots {toc}

−

−### TCC plots shall be on logarithmic axes with current on the horizontal axis and time on the vertical axis, scaled so that the relevant portions of every curve on the sheet are visible.

−### Each plot shall show the following:

−

−- All devices in the coordination pair, drawn in distinct line styles or colors

−- Damage curves and operating envelopes relevant to the pair (transformer through-fault, conductor damage, motor starting and overload)

−- Vertical lines at the available short-circuit currents at the relevant buses, labeled

−- A title block identifying the bus, the devices, the current and voltage base, and the source data

−- A legend identifying every curve and envelope on the sheet

−

−### Plots are [[drawing: per the TCC plot sheets attached to the study report]].

−

−## Consolidated Settings Table {toc}

−

−### The consolidated settings table shall list every adjustable device in the system, every adjustable function on that device, the recommended setting in the units shown on the device, and a reference to the TCC sheet on which the coordination of that setting is demonstrated.

−

−### The consolidated settings table is the master reference for commissioning and for future re-studies; if a setting is not in the table, the study has not made a recommendation about it. {note}

−

−### Settings table is [[drawing: per the protective device settings schedule]].

−

−## Per-Device Settings Sheets {toc}

−

−### For field use during commissioning, the report shall include a one-page settings sheet per device.

−

−### Each sheet shall identify the device by its project tag and physical location, list every adjustable function with its recommended setting, and provide space for the commissioning technician to record the as-set value and to sign.

−

−### The settings sheet is what the technician carries to the breaker and shall not require cross-reference to other parts of the report.

−

−# Re-Study Triggers {toc}

−

−## The protective device coordination study reflects the system as designed and as commissioned. {note}

−## Subsequent changes to the system can invalidate the coordination demonstrated by the study, and the Owner shall have an explicit list of events that trigger a re-study.

−

−## The study shall include a re-study trigger list, written for the Owner's operations staff in non-engineering language.

−

−## At a minimum, the re-study trigger list shall include the events enumerated below.

−

−## Re-Study Trigger Events {toc}

−

−```datasheet

−label: Re-Study Triggers Communicated to Owner

−type: checkbox

−options:

− - "Addition or removal of any generator, UPS, or other on-site source"

− - "Change in utility service capacity or available fault current"

− - "Replacement of a protective device with a different frame or trip type"

− - "Field change to any recommended setting"

− - "Firmware update to a microprocessor relay or trip unit"

− - "Major load addition (typically 25% of bus capacity or more)"

− - "Equipment replacement following a fault event"

− - "Change to the emergency or legally required standby branch (NEC 700.32 / 701.32)"

− - "Change to the project's healthcare essential electrical system (NFPA 99)"

−default:

− - "Addition or removal of any generator, UPS, or other on-site source"

−```

−

−### The 2023 NEC change to 700.32 and 701.32 made the re-evaluation obligation explicit for the emergency and legally required standby branches: when an overcurrent device on those branches is replaced or modified, selective coordination shall be re-verified upstream and downstream.

−

−### The Owner's operations procedures shall reflect the 700.32 / 701.32 re-evaluation obligation, and the re-study trigger list is the bridge between the original study and the procedures.

−

−### Where any trigger event occurs, the Owner shall obtain an updated coordination study, an updated arc-flash study per [[sync/arc-flash-study]], and updated arc-flash labels before the affected portion of the system is returned to normal operation.

−

−# Coordination with Adjacent Scopes {toc}

−

−## Coordination study work intersects with several other electrical and project scopes. {note}

−

−## The Contractor shall coordinate this study with the following scopes so that input data is consistent and so that no scope is asked to commission a device for which no recommended setting has been issued.

−

−## Adjacent Scope Matrix {toc}

−

−| Adjacent scope | Coordination point |

−|----------------|---------------------|

−| [[sync/short-circuit-study]] | Provides input fault currents; study cannot start without it |

−| [[sync/arc-flash-study]] | Consumes coordination settings; runs after coordination |

−| [[sync/low-voltage-switchgear]] | Supplies trip unit data and accepts settings |

−| [[sync/low-voltage-switchboards]] | Supplies trip unit data and accepts settings |

−| [[sync/medium-voltage-switchgear]] | Supplies relay and CT data and accepts settings |

−| [[sync/motor-control-centers]] | Supplies starter overload data and accepts settings |

−| [[sync/emergency-and-standby-power]] | Establishes emergency / standby branches and generator data |

−| [[sync/healthcare-essential-electrical-systems]] | Imposes additional coordination requirements where present |

−| [[sync/electrical-acceptance-testing]] | Verifies as-set values match the study |

+---

+title: Protective Device Coordination Study

+category: Electrical / Power Studies

+description: >

+ When to use: The time-current coordination study for a project's electrical power distribution system, from the utility's protective device at the point of delivery through every overcurrent protective device within the extent the datasheet selects, on AC systems rated 1000 V and below through 38 kV with utility, generator, inverter-based, and paralleled sources. Covers who performs the study and when it is delivered, the degree of coordination applied to normal distribution and the circuits on which NFPA 70 620.62, 645.27, 700.32, 701.32, 708.54, and 517.31(G) require selective coordination, the coordination time intervals and band separations, the curves of the utility device, transformers, motors, conductors, generators, and inverter-based sources that bound every setting, the coordination of ground-fault protection including the two levels NFPA 70 517.17 requires, the recommended setting of every trip unit, relay, fuse, and overload relay, the trade-off between selectivity and incident energy, the coordination deficiencies and who accepts them, the settings record handed to the field, the report, and the events that call for a re-study.

+ Not intended for: the short-circuit study itself, which precedes this one and builds the model this study is run on ([[sync/short-circuit-study]]); the arc-flash hazard analysis itself, which follows this one ([[sync/arc-flash-study]]); the field application and verification of the recommended values on the installed devices ([[sync/electrical-acceptance-testing]]); the classification of the loads served by the emergency and standby sources and the scheme that moves them between sources ([[sync/emergency-and-standby-power]]); the branch topology and the design of a health care essential electrical system ([[sync/healthcare-essential-electrical-systems]]); the distribution assemblies and the overcurrent hardware within them, as products, which each equipment standard governs ([[sync/low-voltage-switchgear]], [[sync/low-voltage-switchboards]], [[sync/panelboards]], [[sync/motor-control-centers]], [[sync/medium-voltage-switchgear]]); the engine-generator as a product and the alternator data it publishes ([[sync/generators]]); the protective relaying scheme design, meaning the choice of relay elements, instrument transformer ratios, and differential and pilot zones, which the Engineer of Record performs in design; load-flow, motor-starting, harmonic, and transient-stability studies; and coordination on the utility's side of the point of delivery.

+---

+# Scope {toc}

+## This standard governs the protective device coordination study as an engineering deliverable: the engineer who performs it and when it is delivered, the degree of coordination the system is held to, the criteria by which two devices in series are judged to coordinate, the equipment curves every setting is bounded by, the setting recommended for every adjustable device and the fuse and overload class selected where the study decides them, the deficiencies the system cannot avoid and who accepts them, the record of settings handed to the field, the report, and the events after which the study is repeated. {note}

+## A coordination study plots the time-current characteristic of every overcurrent device in series between a source and a load on one logarithmic sheet, together with the withstand curves of the transformers, conductors, and motors between them and the fault currents the short-circuit study calculated at each bus, and then chooses each device's settings so that the device nearest a fault opens first and the devices above it stay closed. NFPA 70 240.12 names the orderly shutdown that coordination buys, 700.32, 701.32, 708.54, 620.62, 645.27, and 517.31(G) require full selectivity on the circuits they govern, and on every other circuit the degree of coordination is a design decision this standard asks the project to make in writing rather than discover at the first fault. {note}

+## The coordination study is the second of three studies performed on one system model. The short-circuit study under [[sync/short-circuit-study]] builds the model and calculates the maximum and minimum fault current at every bus; this study takes that model and sets the devices; the arc-flash study under [[sync/arc-flash-study]] takes the settings this study finalizes and turns the clearing time of each device into incident energy. A setting changed here moves the arc-flash labels, which is why the final settings are issued to the arc-flash engineer as a deliverable of this study and not read from a drawing. {note}

+## The following are governed elsewhere and are outside this standard: {note}

+- the system model, the utility's available fault current and X/R, the equipment and conductor data, the source operating cases, and the maximum and minimum fault currents, under [[sync/short-circuit-study]], which this study takes as its input and does not rebuild

+- the incident energy, the arc-flash boundary, and the arc-flash labels, under [[sync/arc-flash-study]], which takes this study's final settings and does not start before they are issued

+- the application of the recommended settings to the installed devices, the party who applies them, and the field verification of every setting before energization, under [[sync/electrical-acceptance-testing]]

+- the trip units, relays, fuses, overload relays, current transformers, and arc energy reduction methods as products, and the ratings the equipment is ordered to, under [[sync/low-voltage-switchgear]], [[sync/low-voltage-switchboards]], [[sync/panelboards]], [[sync/motor-control-centers]], [[sync/combination-motor-starters]], [[sync/medium-voltage-switchgear]], [[sync/metal-enclosed-interrupter-switchgear]], [[sync/secondary-unit-substations]], [[sync/generator-paralleling-switchgear]], [[sync/automatic-transfer-switches]], [[sync/busway]], and the other equipment standards that name this study

+- the classification of the emergency, legally required standby, and optional standby loads and the transfer scheme that serves them, under [[sync/emergency-and-standby-power]], which names the systems whose devices this study coordinates selectively

+- the branch topology of a health care essential electrical system and the second level of ground-fault protection as equipment, under [[sync/healthcare-essential-electrical-systems]] and [[sync/electrical-service-entrance]]; this study sets and coordinates both levels

+- the generator set, its alternator, its excitation system, and the decrement curve the manufacturer publishes, under [[sync/generators]]; this study plots that curve and sets the devices the set feeds

+- the fire pump controller and the sizing of the fire pump branch overcurrent device, under [[sync/fire-pump-controllers]] and [[sync/fire-pumps]]; this study plots that device and coordinates the devices above it

+- the design of the protective relaying scheme, meaning which relay elements are furnished at each breaker, the current and voltage transformer ratios, and the zones of differential and pilot protection, which the Engineer of Record performs in design and which this study takes as furnished

+- load-flow, voltage-drop, motor-starting, harmonic, and transient-stability studies, and the coordination of devices on the utility's side of the point of delivery

+## The study shall extend from the utility's protective device at the point of delivery through every overcurrent protective device shown on [[drawing: the one-line diagram]] within the extent selected under Study Extent, on every source and in every operating case the short-circuit study calculated.

+# Referenced Standards {toc}

+## The study, its settings, and its report shall comply with the latest adopted edition of each of the following unless a specific edition is cited.

+## Where the contract documents, the adopted edition of NFPA 70, the serving utility's requirements, or two referenced standards impose conflicting requirements, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

+| Standard | Title |

+|----------|-------|

+| NFPA 70 | National Electrical Code (Articles 230, 240, 430, 450, 517, 620, 645, 695, 700, 701, and 708) |

+| NFPA 70E | Standard for Electrical Safety in the Workplace |

+| NFPA 20 | Standard for the Installation of Stationary Pumps for Fire Protection |

+| NFPA 99 | Health Care Facilities Code |

+| NFPA 110 | Standard for Emergency and Standby Power Systems |

+| IEEE 242 | Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems (Buff Book) |

+| IEEE 3004.5 | Recommended Practice for the Application of Low-Voltage Circuit Breakers in Industrial and Commercial Power Systems |

+| IEEE 3004.8 | Recommended Practice for Motor Protection in Industrial and Commercial Power Systems |

+| IEEE 1584 | Guide for Performing Arc-Flash Hazard Calculations |

+| IEEE C37.2 | Standard Electrical Power System Device Function Numbers, Acronyms, and Contact Designations |

+| IEEE C37.13 | Low-Voltage AC Power Circuit Breakers Used in Enclosures |

+| IEEE C37.17 | Trip Systems for Low-Voltage (1000 V and below) AC and General Purpose (1500 V and below) DC Power Circuit Breakers |

+| IEEE C37.90 | Relays and Relay Systems Associated with Electric Power Apparatus |

+| IEEE C37.91 | Guide for Protecting Power Transformers |

+| IEEE C37.96 | Guide for AC Motor Protection |

+| IEEE C37.102 | Guide for AC Generator Protection |

+| IEEE C37.112 | Inverse-Time Characteristic Equations for Overcurrent Relays |

+| IEEE C57.109 | Guide for Liquid-Immersed Transformers Through-Fault-Current Duration |

+| IEEE C57.12.59 | Guide for Dry-Type Transformer Through-Fault Current Duration |

+| ICEA P-32-382 | Short-Circuit Characteristics of Insulated Cable |

+| ICEA P-45-482 | Short-Circuit Performance of Metallic Shields and Sheaths on Insulated Cable |

+| NEMA ICS 2 | Industrial Control and Systems: Controllers, Contactors, and Overload Relays Rated 600 Volts |

+| NEMA MG 1 | Motors and Generators |

+| UL 489 | Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures |

+| UL 248 | Low-Voltage Fuses |

+| UL 1066 | Low-Voltage AC and DC Power Circuit Breakers Used in Enclosures |

+| ANSI/NETA ATS | Acceptance Testing Specifications for Electrical Power Equipment and Systems |

+# Submittals {toc}

+## Action Submittals {toc}

+### The Contractor shall submit the following for review by the Engineer of Record:

+- the qualifications of the study engineer, where the datasheet under Study Engineer selects an engineer other than the one performing the short-circuit study, giving the license, the firm, and the comparable studies described under Study Engineer

+- the coordination criteria statement, giving the degree of coordination applied to normal distribution, the circuits identified as requiring selective coordination, the coordination time intervals and band separations, the instantaneous-region selectivity basis, and the setting priority the datasheet selects, as the study will apply them

+- the study report described under Study Report, with the time-current curve sheets, the settings table, and the deficiency list

+- the equipment change list, naming every device whose frame, trip unit, fuse class, or rating must change from the equipment submittal to achieve the coordination required, with the equipment standard and submittal each change belongs to

+```datasheet

+label: Action Submittals

+type: checkbox

+options:

+ - "Study engineer qualifications"

+ - "Coordination criteria statement"

+ - "Study report with curve sheets, settings table, and deficiency list"

+ - "Equipment change list"

+default:

+ - "Coordination criteria statement"

+ - "Study report with curve sheets, settings table, and deficiency list"

+ - "Equipment change list"

+constraint: all_of

+```

+### The coordination criteria statement shall be reviewed and returned before the curves are plotted, and the study report shall not be submitted until the statement covering it has been returned.

+### The criteria statement is a page, and it settles the arguments the report would otherwise start: whether an overlap in the instantaneous region is a deficiency or an accepted condition, whether 0.3 s or 0.4 s separates two relays, and which circuits must coordinate at every current. A report reviewed against criteria the reviewer never agreed to is reviewed twice. {note}

+### Where the datasheet under Circuits Requiring Selective Coordination identifies any circuit, the study report shall be submitted and returned before the overcurrent devices on those circuits are released for manufacture.

+## Closeout Submittals {toc}

+### The Contractor shall submit the following before the equipment within the study extent is accepted:

+- the final study report, revised to the settings as left in service under [[sync/electrical-acceptance-testing]], with every departure from the recommended setting listed and the coordination at the as-left value demonstrated

+- the final settings record in the formats the datasheet selects under Settings Record Format

+- the native model files of the analysis software, carrying the final settings, with the software version and device library revision that produced the report

+- the written acceptance of the Engineer of Record for every coordination deficiency accepted under Coordination Deficiencies

+- the re-study trigger list described under Study Revisions and Re-Study Triggers, written for the Owner's operations staff

+- the documentation that NFPA 70 700.32, 701.32, 708.54, 620.62, and 645.27 require to be made available for the selective coordination of the circuits they govern, where any such circuit is on the project

+```datasheet

+label: Closeout Submittals

+type: checkbox

+options:

+ - "Final study report at as-left settings"

+ - "Final settings record"

+ - "Native model files with final settings"

+ - "Engineer of Record acceptance of each coordination deficiency"

+ - "Re-study trigger list"

+ - "Selective coordination documentation for code-governed circuits"

+default:

+ - "Final study report at as-left settings"

+ - "Final settings record"

+ - "Native model files with final settings"

+ - "Engineer of Record acceptance of each coordination deficiency"

+ - "Re-study trigger list"

+ - "Selective coordination documentation for code-governed circuits"

+constraint: all_of

+```

+### The native model files shall be delivered in a form the Owner can open and edit with a licensed copy of the software, without a password, a locked library, or a dependency on the study engineer's account.

+### The settings a system runs on are the ones in the trip units, not the ones in the report, and the two drift apart on the day a technician cannot reach a recommended value and picks the nearest one. A closeout report revised to the as-left values is the only document that describes the system as it stands, and the model that carries those values is what the next engineer opens when a breaker is replaced. {note}

+# Quality Assurance {toc}

+## Study Engineer {toc}

+### The study shall be performed by the study engineer indicated in the datasheet.

+```datasheet

+label: Study Engineer

+type: select

+options:

+ - "The engineer performing the short-circuit study"

+ - "Engineer of Record"

+ - "Independent engineer engaged by the Contractor"

+ - "Equipment manufacturer's engineering services"

+ - "Testing organization's engineering group"

+default: "The engineer performing the short-circuit study"

+```

+### The three studies are built on one model, and the engineer who built it for the short-circuit study already holds every impedance, every device, and every assumption this study needs, which is why one engineer performs all three on nearly every project and the short-circuit study standard is where that engineer is chosen; the Engineer of Record performs the coordination study separately where the settings decide the design, as on a system whose selective coordination governs the choice between power breakers and molded-case breakers; an independent engineer engaged by the Contractor is the arrangement where the coordination study is priced as a construction deliverable and built from the devices actually furnished; the equipment manufacturer's engineering services know their own trip units and their own selectivity tables best and are the only party with the published data for some pairs, and their settings for other makers' devices and for the relays rest on the data handed to them; the testing organization's engineering group puts the settings and the test set in one firm's hands, so that the party injecting each trip unit computed the value it is set to. {note}

+### The study shall be performed under the responsible charge of a Professional Engineer licensed in the jurisdiction of the project, and the report, the curve sheets, and the settings table shall bear that engineer's seal and signature.

+### Where the datasheet selects an engineer other than the one performing the short-circuit study, the study engineer shall have performed not fewer than five coordination studies on systems of the same voltage class and of comparable size within the five years before the study, and shall name them in the qualifications.

+### Where the equipment manufacturer's engineering services perform the study, the study shall set every device within the study extent, whether or not the manufacturer furnished it, and a study limited to the manufacturer's own equipment shall not be accepted.

+### Where the study engineer is not the Engineer of Record, the Engineer of Record shall review the study report and return it before any setting it recommends is applied to a device.

+### Where the study engineer and the Engineer of Record disagree on a criterion, a setting, or the acceptance of a deficiency, the Engineer of Record shall make the determination and the study shall record it in the report.

+## Model, Software, and Delivery {toc}

+### The study shall be performed on the model the short-circuit study delivers under [[sync/short-circuit-study]], in the analysis software and at the device library revision that study identifies, and shall not be started until that study has been reviewed and returned.

+### Where the short-circuit study was performed by hand calculation, the coordination study shall be performed in commercial power system analysis software on a model built from the short-circuit study's one-line diagram, input data tables, and results, and the model shall be verified against those results at the service equipment and at the secondary of every transformer before any curve is plotted.

+### The device library shall contain the published time-current characteristic of every device within the study extent at the revision the manufacturer currently publishes, and a device not in the library shall be entered from the manufacturer's published curve data, with the source curve included in the report appendix.

+### The study shall be delivered at the stage the short-circuit study is delivered under [[sync/short-circuit-study]], and where that study is delivered before equipment release with an as-built update, the coordination study shall be re-run on the updated model and re-issued before the equipment within the study extent is energized.

+### Where the short-circuit study is delivered after installation, the Contractor shall furnish the coordination study and the settings record before any device within the study extent is energized, and no device shall be energized at its shipping settings.

+### A coordination study drawn by hand or in general plotting software cannot be checked against the published characteristic of the device, and a study run on a model that differs from the short-circuit study's gives a clearing time at a fault current that was never calculated. One model, one library, and one chain of custody from the first study to the arc-flash label is the whole reason the three studies are specified as a sequence. {note}

+## Study Extent {toc}

+### The study shall extend downstream through the devices indicated in the datasheet.

+```datasheet

+label: Study Extent

+type: select

+options:

+ - "Through the main device of every panelboard and motor control center"

+ - "Through the largest branch or feeder device of every panelboard and the branch device of every individually modeled motor"

+ - "Through every overcurrent device, including every branch circuit device"

+default: "Through the largest branch or feeder device of every panelboard and the branch device of every individually modeled motor"

+```

+### Stopping at the main of each panelboard sets every feeder and every main and leaves the branch devices to the manufacturer's curves, which is the extent of a study whose purpose is the settings of the adjustable devices; carrying the study through the largest device in each panelboard and through the branch device of each motor large enough to be modeled on its own checks the pair that is most likely to overlap, the largest branch breaker against the feeder above it, and costs one more curve per panelboard, which is why most studies draw the line there; plotting every branch device, down to the lighting and receptacle circuits, is the extent that the selective coordination articles of NFPA 70 require on the circuits they govern, and on normal distribution it multiplies the sheets without changing a setting. {note}

+### On every circuit the datasheet identifies under Circuits Requiring Selective Coordination, the study shall extend through every overcurrent device to the load, including every branch circuit device, regardless of the extent selected above.

+### Motors modeled individually shall be the motors at or above the threshold the short-circuit study selects under [[sync/short-circuit-study]], and the branch device and overload relay of every such motor shall be within the study extent.

+# Coordination Criteria {toc}

+## Degree of Coordination {toc}

+### Overcurrent devices in series on normal distribution shall be coordinated to the degree indicated in the datasheet.

+```datasheet

+label: Degree of Coordination, Normal Distribution

+type: radio

+options:

+ - "Selective for the full range of overcurrents to the maximum available fault current"

+ - "Selective for overcurrents whose duration extends beyond 0.1 s"

+ - "Selective for overcurrents whose duration extends beyond 0.01 s"

+ - "Coordinated to the extent the devices furnished permit, with every overlap documented"

+```

+### Selectivity for the full range of overcurrents, as NFPA 70 Article 100 defines selective coordination, means that at every current from the lowest overload to the maximum available fault current the downstream device clears before the upstream device begins to open, which on low-voltage systems is reached with power circuit breakers carrying short-time delay, with fuses selected by ratio, or with molded-case breakers whose tested selectivity tables cover the pair, and which is the degree the code requires on the circuits it names; selectivity beyond 0.1 s ignores the overlap in the instantaneous region of two molded-case breakers for faults that clear in less than 0.1 s, on the ground that a fault at the available current clears so fast that the loss of the upstream device is accepted, and it is the degree NFPA 70 517.31(G) states for the health care essential electrical system; selectivity beyond 0.01 s ignores only the overlap below one half cycle, where the instantaneous elements of two breakers both unlatch, and is the degree a project chooses where it wants selectivity through the short-time region without buying the selectivity tables; coordination to the extent the devices permit sets every adjustable device as well as the system allows, documents each overlap with its current range, and is the degree a normal distribution system is held to where an upstream trip on a bolted fault is an inconvenience and not a hazard. No one degree is the norm for normal distribution, and the choice turns on what a fault on a feeder is allowed to take down. {note}

+### Whatever degree the datasheet selects, every device shall operate for the minimum fault current at the far end of the circuit it protects, as the short-circuit study calculates it, within the time the conductor damage curve of that circuit allows.

+### A device that does not operate for the minimum fault at the end of its circuit leaves an arcing fault to burn until the next device upstream sees it, and the study checks the low end of every curve for that reason as carefully as the high end. The minimum case of the short-circuit study, on the generator alone and with the motors removed, is where the far-end fault is smallest. {note}

+## Circuits Requiring Selective Coordination {toc}

+### The overcurrent devices on every circuit indicated in the datasheet shall be selectively coordinated with all supply-side overcurrent protective devices for the full range of overcurrents, as the article of NFPA 70 that governs that circuit requires, regardless of the degree selected for normal distribution.

+```datasheet

+label: Circuits Requiring Selective Coordination

+type: checkbox

+derived: "the systems shown on the one-line diagram and the articles of NFPA 70 that classify them"

+options:

+ - "Emergency system, NFPA 70 700.32"

+ - "Legally required standby system, NFPA 70 701.32"

+ - "Critical operations power system, NFPA 70 708.54"

+ - "Health care essential electrical system, NFPA 70 517.31(G)"

+ - "Elevator feeders serving more than one driving machine disconnecting means, NFPA 70 620.62"

+ - "Critical operations data system, NFPA 70 645.27"

+default: derived

+constraint: all_of

+```

+### Which circuits must be selectively coordinated is not a choice the study makes; it follows from the systems the one-line diagram shows and the articles that classify them, which the emergency power standard and the health care standard settle. The study takes the classification and demonstrates the coordination. {note}

+### On a health care essential electrical system, the selective coordination shall be demonstrated by the rule NFPA 70 517.31(G) states, and the time threshold that article applies shall be stated in the criteria statement.

+### The study shall apply an exception of NFPA 70 700.32, 701.32, or 708.54 to a pair only where the report cites the exception in the adopted edition and documents the condition that satisfies it for that pair.

+### The exception for two devices in series with no load connected between them is the common case: a feeder breaker and the main of the panelboard it feeds alone remove the same loads whichever one opens, so the code does not ask them to coordinate with each other, and a study that treats that pair as a deficiency finds one where the code sees none. {note}

+### Selective coordination on a circuit the datasheet identifies shall be demonstrated on every source that can supply it, including the alternate source alone, at the fault currents the short-circuit study calculates for that source.

+### A series-rated combination shall not be applied on a circuit the datasheet identifies, and a series-rated combination that the short-circuit study proposes as the remediation of a deficiency on any other circuit shall be reported by this study as non-selective at the currents above the instantaneous pickup of the upstream device before it is accepted.

+### Where the devices furnished on a circuit the datasheet identifies cannot be coordinated selectively, the study shall report the device changes that achieve it and the Engineer of Record shall direct them.

+### The selective coordination of the circuits the datasheet identifies shall be documented in the report in the form NFPA 70 requires to be made available to those who design, install, inspect, maintain, and operate the system, and the closeout submittal of the report is how this standard meets that requirement.

+## Coordination Time Intervals {toc}

+### Where an inverse-time relay is the upstream device, the study shall maintain not less than the interval indicated in the datasheet between the relay's operating curve and the maximum clearing curve or band of the downstream device, at every current at which both operate.

+```datasheet

+label: Coordination Time Interval, Electromechanical Relay Upstream

+type: range

+unit: s

+options:

+ min: 0.2

+ max: 0.6

+ setpoints: [0.2, 0.25, 0.3, 0.35, 0.4, 0.5, 0.6]

+default: 0.4

+constraint: min

+```

+```datasheet

+label: Coordination Time Interval, Microprocessor Relay Upstream

+type: range

+unit: s

+options:

+ min: 0.15

+ max: 0.5

+ setpoints: [0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5]

+default: 0.3

+constraint: min

+```

+### The interval between two relays is built from parts: the opening time of the upstream breaker, about five cycles on a medium-voltage breaker; the overtravel of an induction disc that keeps turning after the fault is cleared, about 0.1 s; the tolerance of the relay and its current transformer; and a safety margin. IEEE 242 arrives at about 0.4 s for an electromechanical relay and about 0.3 s for a microprocessor relay, which has no overtravel, and those are the figures most studies use without discussion; an interval of 0.2 to 0.25 s is used where the relays are field-calibrated and the breaker opening time is known, and every 0.1 s saved at one level is 0.1 s saved at every level above it; a longer interval buys margin against an uncalibrated relay at the cost of a slower main and a higher incident energy at every bus the main protects. {note}

+### Where a fuse is the downstream device, the interval shall be measured from the total clearing curve of the fuse to the operating curve of the upstream relay, and shall be not less than the interval indicated in the datasheet.

+```datasheet

+label: Coordination Time Interval, Relay Upstream of a Fuse

+type: range

+unit: s

+options:

+ min: 0.1

+ max: 0.4

+ setpoints: [0.1, 0.15, 0.2, 0.25, 0.3, 0.4]

+default: 0.2

+constraint: min

+```

+### A fuse's total clearing curve already includes its arcing time, and the upstream relay need only not have operated by the time the fuse clears, so the opening time of the upstream breaker drops out of the interval; what remains is the relay's overtravel and tolerance, about 0.2 s for an electromechanical relay and 0.1 to 0.15 s for a microprocessor relay. {note}

+### Where two low-voltage circuit breakers with published clearing bands are in series, the study shall demonstrate that the minimum clearing band of the upstream device sits above the maximum clearing band of the downstream device with not less than the separation indicated in the datasheet, at every current at which both operate.

+```datasheet

+label: Band Separation, Low-Voltage Trip Units in Series

+type: range

+unit: s

+options:

+ min: 0

+ max: 0.1

+ setpoints: [0, 0.02, 0.03, 0.05, 0.1]

+default: 0

+constraint: min

+```

+### The published band of a low-voltage trip unit already contains the tolerance of the sensor, the trip unit, and the mechanism, so two bands that do not touch are coordinated with no further allowance, and a separation of zero is the practice on nearly every study; a project adds a separation where the trip units are of different makes whose bands were measured under different test standards, or where it wants a visible gap on the sheet for the reviewer. {note}

+### Where two fuses are in series, the study shall demonstrate selectivity by the manufacturer's published selectivity ratio tables for the fuse classes and speeds of the pair, and where the pair is not covered by a table, by the total clearing curve of the downstream fuse against the minimum melting curve of the upstream fuse at every current.

+### The minimum melting curve of an upstream fuse shall be reduced for preloading and ambient temperature by the factor the manufacturer publishes, and where the manufacturer publishes none, its melting time shall be reduced by 25 percent before the comparison is made.

+### A fuse that has been carrying load is part way to melting before the fault arrives, and a fuse in a hot enclosure melts sooner still. The published minimum melting curve is drawn for a cold fuse at room temperature, so a study that compares it unadjusted shows a margin the fuse does not have. {note}

+### A selectivity ratio table applies only to two fuses of the manufacturer that published it, and where the study relies on a table, the report shall state that both fuses of the pair are to be of one manufacturer and the settings record shall carry that restriction against each position.

+## Instantaneous-Region Selectivity {toc}

+### Where the time-current curves of two low-voltage circuit breakers overlap in the instantaneous region, the study shall establish selectivity in that region on the basis indicated in the datasheet.

+```datasheet

+label: Instantaneous-Region Selectivity Basis

+type: radio

+options:

+ - "Manufacturer's published selectivity tables for the tested pair accepted"

+ - "Time-current curves only"

+default: "Manufacturer's published selectivity tables for the tested pair accepted"

+```

+### The published curve of a molded-case breaker stops at the instantaneous pickup, and two such curves overlap at every current above the lower pickup, yet the pair is often selective in a test because the downstream breaker is current-limiting and clears before the upstream element unlatches. Manufacturers publish selectivity tables, built from tests of each pair, that state the current up to which the pair is selective, and nearly every study accepts them because a system of molded-case breakers cannot be shown selective any other way; a project that accepts the curves alone treats every instantaneous overlap as a deficiency, which is the posture of an Owner who does not want selectivity to depend on both breakers staying the make and type that were tested. {note}

+### Where the tables are accepted, the study shall cite the table, its revision, and the tested pair for every position whose selectivity rests on it, and the settings record shall carry against each such position the make and type of both devices the table requires.

+### Where the tables are accepted and the available fault current at the downstream device exceeds the current the table states for the pair, the pair shall be reported as a deficiency above that current.

+## Selectivity and Incident Energy {toc}

+### Where a setting that achieves the coordination required raises the incident energy at a bus, and a setting that lowers the incident energy loses the coordination, the study shall resolve the pair by the priority indicated in the datasheet on normal distribution.

+```datasheet

+label: Setting Priority Where Selectivity and Incident Energy Conflict

+type: radio

+options:

+ - "Selectivity, with the incident energy addressed by arc energy reduction and work practices"

+ - "Incident energy, with the overlap documented as a coordination deficiency"

+ - "Resolved pair by pair by the Engineer of Record"

+```

+### Every second of delay a main is given so that a feeder can clear first is a second an arc on the main bus burns, and the two studies that share this model pull the same setting in opposite directions. Holding selectivity and reducing the energy another way, with zone-selective interlocking that drops the delay when no feeder sees the fault, a maintenance switch during work, or differential relaying, keeps the system up through a feeder fault and is the posture of a facility that cannot lose a bus, at the cost of the arc energy reduction equipment the equipment standards carry; holding the incident energy lets the main trip on a feeder fault in exchange for a lower category at every piece of equipment on that bus, and is the posture of a facility whose work is done live and whose feeders can be lost; resolving each pair with the Engineer of Record is the arrangement where the buses differ, a data hall on one feeder and a loading dock on another. The incident energy itself is calculated under the arc-flash study, which is why this field decides the priority and not the number. {note}

+### On every circuit the datasheet identifies under Circuits Requiring Selective Coordination, the selective coordination shall govern, and the incident energy shall be addressed by the arc energy reduction method the equipment standard selects and by the arc-flash study.

+### Where an equipment standard selects zone-selective interlocking as its arc energy reduction method, the study shall set the restrained and the unrestrained short-time and ground-fault delays of every participating trip unit and shall demonstrate that the coordination required is held with the interlock in service and with it failed to restrained.

+### Where an equipment standard selects an energy-reducing maintenance switch, the study shall demonstrate the coordination required with the switch in its normal position and shall state the setting the switch applies in its maintenance position on the settings record.

+### Where an equipment standard selects an instantaneous trip or an instantaneous override set below the available arcing current as its arc energy reduction method under NFPA 70 240.87(B), the study engineer shall obtain the minimum arcing current at that equipment from the engineer performing the arc-flash study under [[sync/arc-flash-study]], shall set the pickup below it, and shall include the documentation NFPA 70 240.87(A) requires in the report.

+### A maintenance switch lowers the pickup only while a worker remembers to turn it on, and the study coordinates the system for the other 99 percent of its life; a zone-selective interlock pays the short-time delay only when a downstream trip unit reports that it sees the fault, so it is the one method that gives up nothing in either study, and it needs the trip units above and below to be wired to each other, which the equipment standards carry. {note}

+# Equipment and Source Curves {toc}

+## Utility Protective Device {toc}

+### The Contractor shall request from the serving utility, in writing, the time-current characteristic and the settings of the utility's protective device immediately upstream of the point of delivery, and shall include the request and the response in the report.

+### The service overcurrent device shall be coordinated with the utility's protective device as indicated in the datasheet.

+```datasheet

+label: Coordination With the Utility Protective Device

+type: radio

+options:

+ - "Required, service device set to clear before the utility device"

+ - "Utility device plotted for information, service device not held below it"

+```

+### A utility that furnishes the curve of its fuse or recloser usually asks the customer's service device to clear first, so that a fault inside the building does not open the utility's device and take the neighbors with it, and the service main is then set below the utility curve as the first constraint of the whole study; a utility that furnishes nothing, or one whose device is a substation breaker set far above the service, is plotted for information and the service device is set from the equipment it protects. The utility's curve is the one input this study owns outright, because the short-circuit study needs only the utility's fault current and X/R and never asks for the curve. {note}

+### Where the utility declines to furnish the characteristic of its device, the study shall record the request and the response, shall set the service device to the maximum the utility's published service requirements permit where it states one, and shall report that coordination with the utility device was not demonstrated.

+## Transformers {toc}

+### For every transformer within the study extent, the through-fault protection curve of IEEE C57.109 for a liquid-immersed unit or IEEE C57.12.59 for a dry-type unit shall be plotted on the sheet that carries the transformer's primary and secondary devices, for the category that guide assigns to the transformer's kVA.

+### The through-fault curve of a transformer within the categories for which the guides publish two curves shall be the curve indicated in the datasheet.

+```datasheet

+label: Transformer Through-Fault Curve Applied

+type: radio

+options:

+ - "Infrequent-fault incidence curve"

+ - "Frequent-fault incidence curve"

+default: "Infrequent-fault incidence curve"

+```

+### The guides publish one curve for a transformer whose secondary rarely sees a through fault, which is the transformer inside a building feeding switchgear and cable, and a lower curve for a transformer whose secondary feeds overhead lines or a process where faults are a matter of routine, on the ground that the winding's mechanical life is spent one through fault at a time. The infrequent curve is the one nearly every building transformer is protected to, and the frequent curve is applied to a unit whose secondary serves exposed conductors or a load with a history of faults. {note}

+### Where a transformer's secondary serves overhead conductors or a load the Engineer of Record designates as subject to frequent faults, the frequent-fault incidence curve shall be applied to that transformer regardless of the datasheet selection.

+### The through-fault curve shall be shifted for the transformer's connection when the primary device is compared against it for a secondary line-to-ground fault, so that a delta-wye transformer's curve is plotted at 58 percent of its three-phase value on the primary side.

+### The primary overcurrent device shall clear a bolted fault at the secondary terminals, in the maximum case, before the through-fault curve is reached, and the secondary overcurrent device, where one is furnished, shall clear a fault at the end of the secondary conductors before the curve is reached.

+### The magnetizing inrush of every transformer shall be plotted on the primary side as a point at the multiple of rated full-load current indicated in the datasheet for a duration of 0.1 s, and the primary device shall not operate at that point.

+```datasheet

+label: Transformer Inrush Point

+type: range

+unit: × full-load current

+options:

+ min: 8

+ max: 25

+ setpoints: [8, 10, 12, 25]

+default: 12

+constraint: exact

+```

+### A transformer energized at the wrong point on the voltage wave draws a magnetizing current that a primary fuse or relay cannot tell from a fault, and the inrush point is where the study makes sure the primary device rides through it. Twelve times full-load current for 0.1 s is the figure IEEE C37.91 gives for most distribution transformers and the one nearly every study plots; 8 times is the figure for a small unit or one the manufacturer has measured lower; 25 times is the first half-cycle peak that a fast fuse or an instantaneous element on a large unit is checked against at 0.01 s in addition to the 0.1 s point. Where the manufacturer publishes the inrush of the unit furnished, that value governs. {note}

+### Where the transformer manufacturer publishes the inrush characteristic of the unit furnished, that characteristic shall be plotted in place of the datasheet point.

+### The rating of a primary or secondary device and the setting of a primary relay shall not exceed the maximum NFPA 70 450.3 permits for the transformer's voltage, impedance, and supervision, and the study shall state the NFPA 70 450.3 limit against each transformer in the settings table.

+### Where the primary device is a fuse, the study shall select the fuse's ampere rating and speed from the inrush point, the through-fault curve, the NFPA 70 450.3 limit, and the secondary device's curve, and the selection shall be delivered to the equipment standard that furnishes the fuse.

+## Motors and Motor Controllers {toc}

+### For every individually modeled motor, the study shall plot the motor's starting current for its acceleration time, from the locked-rotor current and the starting method furnished, together with the motor's thermal limit curve where the manufacturer publishes one and the overload relay's trip curve at the recommended setting, on the sheet that carries the motor's branch overcurrent device.

+### The overload relay's trip curve shall lie above the starting curve and below the motor's thermal limit curve, and where the manufacturer publishes no thermal limit curve, the study shall apply the locked-rotor time at the motor's locked-rotor current as the limit.

+### The study shall recommend the setting of every adjustable overload relay for the full-load current, the service factor, and the temperature rise of the motor served, within the limits of NFPA 70 430.32, starting from the trip class the equipment standard selects for the controller and changing the class only where the starting curve or the thermal limit curve of the motor requires it, with the change delivered to that equipment standard.

+### The branch overcurrent device of every motor shall be set or selected within the limits of NFPA 70 430.52, and where an instantaneous-trip circuit breaker is furnished, the study shall set its pickup above the motor's asymmetrical inrush and shall not exceed the percentage NFPA 70 430.52(C)(3) permits for the motor's design letter.

+### Where a soft starter or a drive supplies the motor, the study shall plot the current limit of the starter or drive as the starting curve, and where the controller carries a bypass, shall plot the across-the-line starting curve for the bypass as well.

+### For a medium-voltage motor, the study shall set the motor protection relay's thermal, locked-rotor, overcurrent, and ground-fault elements in accordance with IEEE C37.96 from the data the motor manufacturer publishes, and shall plot them against the motor's starting and thermal limit curves and the upstream device.

+### A motor's overload relay is set from the motor's nameplate, and the trip class is selected from how long the motor takes to start; the study does not choose either from the code limits alone, because a relay that meets 430.32 and trips on every start protects nothing. The equipment standards select the class the controller is furnished with, and this study is where the selection is checked against the motor that is actually driven. {note}

+## Conductors {toc}

+### The short-circuit damage curve of ICEA P-32-382 shall be plotted for the conductors indicated in the datasheet, for the conductor material, insulation temperature rating, and size of each run, on the sheet that carries the device protecting the run.

+```datasheet

+label: Conductor Damage Curves Plotted

+type: select

+options:

+ - "Every service conductor and feeder"

+ - "Every service conductor, feeder, and motor branch circuit"

+ - "Every conductor protected by a device with a short-time delay or by a time-delayed relay"

+default: "Every service conductor and feeder"

+```

+### A conductor's damage curve is the limit the device above it must clear beneath, and the conductor that is at risk is the one whose protecting device waits: a feeder from a main with a short-time delay, a service conductor under a relay with a time dial, or a motor branch circuit whose instantaneous-trip breaker is set high for the inrush. Plotting every service conductor and feeder covers the conductors large enough to matter and the devices most likely to be delayed, and is the extent most studies plot; adding the motor branch circuits covers the conductor under a high-set instantaneous-trip breaker; limiting the plot to conductors under a delayed device plots only the runs that can fail the check and is the extent of a study with hundreds of feeders under instantaneous devices. {note}

+### The device protecting a run shall clear the maximum fault current at the near end of the run before the damage curve is reached, and the minimum fault current at the far end of the run before the damage curve is reached at that current.

+### For a shielded medium-voltage cable, the short-circuit withstand of the shield under ICEA P-45-482 shall be plotted against the ground-fault clearing time of the device protecting the cable at the maximum line-to-ground fault current.

+### Where the cable manufacturer publishes a damage curve for the cable furnished that is more restrictive than the ICEA curve, the manufacturer's curve shall govern.

+## Generators and Inverter-Based Sources {toc}

+### For every generator within the study extent, the study shall plot the decrement curve of the alternator furnished, as the generator standard requires the manufacturer to state it, on every sheet that carries a device the generator supplies alone, and shall demonstrate that every such device clears a fault in the minimum case before the decrement curve falls below the device's pickup.

+### Where the decrement curve of a shunt-excited alternator falls below the pickup of a device the set feeds before that device operates, the study shall report the device to the Engineer of Record as one that does not clear on generator power, with the excitation change, the setting change, or the device change that resolves it.

+### The study shall set the overcurrent, voltage-restrained or voltage-controlled overcurrent, and ground-fault elements of every generator breaker and generator protection relay in accordance with IEEE C37.102 from the data the generator manufacturer publishes, and shall coordinate them with the devices the generator supplies in the generator-alone and paralleled cases.

+### Where paralleling switchgear is furnished, the study shall set every protective function of its generator and bus relays, including the reverse-power, under- and overvoltage, under- and overfrequency, loss-of-excitation, and differential functions the equipment standard furnishes, from the alternator and engine data the manufacturer publishes and the paralleling scheme the equipment standard describes, and shall deliver the settings on the settings record that standard requires.

+### Where a generator breaker carries a ground-fault function on a set serving other than an Article 700 system, the study shall set its pickup and delay to coordinate with the ground-fault devices downstream, and where the set serves an Article 700 system, the study shall record the ground-fault function as indication only, as NFPA 70 700.31 and the generator standard require.

+### A generator supplies a fault current that falls within seconds to a value near its full-load rating, and a feeder device set on utility power to trip at ten times the generator's rating may never see that current on generator power. Every device the generator feeds alone is checked against the decrement curve for that reason, and the check is where a shunt-excited alternator or a thermal-magnetic generator breaker is found out. {note}

+### For every uninterruptible power supply, energy storage inverter, and photovoltaic inverter within the study extent, the study shall plot the current limit and its duration as the manufacturer publishes them, and shall demonstrate that every device the source supplies in inverter operation clears a fault within that duration or shall report the device as dependent on the source's bypass for fault clearing.

+### For every transfer switch within the study extent, the settings record shall identify the overcurrent device immediately upstream on each source, with its settings, so that the withstand and closing rating of the switch under [[sync/automatic-transfer-switches]] is evaluated against the device that actually protects it on each source.

+## Fire Pump Circuits {toc}

+### The study shall plot the fire pump branch overcurrent device and the fire pump controller's overcurrent device as sized under NFPA 70 695.4(B)(2), NFPA 20, and the fire pump controller standard, and shall not recommend a setting or a rating for either that is below what those articles require.

+### Every overcurrent device upstream of the fire pump branch device shall be set to coordinate with it for a fault on the fire pump circuit, and the study shall demonstrate that a fault elsewhere on the system does not open the device that supplies the fire pump.

+### The fire pump device is sized to carry the locked-rotor current of the pump motor indefinitely, which produces a curve that protects nothing downstream and is not meant to; the code chooses a burned pump motor over a dark sprinkler riser. The study's job on that circuit is to keep every device above it from opening first. {note}

+# Ground-Fault Coordination {toc}

+## Ground-Fault Protection Levels {toc}

+### Where ground-fault protection of equipment is furnished on two or more devices in series, the study shall coordinate the ground-fault functions on separate curve sheets from the phase coordination, at the maximum and minimum line-to-ground fault currents the short-circuit study calculates.

+### The pickup and the time delay of the ground-fault protection at the service shall be set by this study within the limits of NFPA 70 230.95(A), with a pickup not exceeding 1200 A and a maximum time delay not exceeding one second for a ground-fault current of 3000 A or more, and the setting shall be delivered to [[sync/electrical-service-entrance]] for the service equipment.

+### Where a second level of ground-fault protection is furnished on a feeder, the feeder's ground-fault function shall clear a ground fault on that feeder before the service device's ground-fault function operates, with the separation between their operating bands indicated in the datasheet.

+```datasheet

+label: Ground-Fault Band Separation, Two Levels in Series

+type: range

+unit: cycles

+options:

+ min: 6

+ max: 18

+ setpoints: [6, 9, 12, 18]

+default: 6

+constraint: min

+```

+### NFPA 70 517.17(C) requires a six-cycle minimum separation between the operating time bands of the two levels of ground-fault protection on a health care essential electrical system, and six cycles is the separation nearly every two-level scheme is set to, because the service device is already held to one second at 3000 A and every cycle added below it is taken from the feeder; a longer separation is used where the two devices are of different makes whose bands were measured differently, or where a third level below the feeder needs room of its own. {note}

+### Where a health care facility is served, the second level of ground-fault protection shall be coordinated with the service level as NFPA 70 517.17 requires, and the pickup and time delay of each level shall be delivered to [[sync/healthcare-essential-electrical-systems]] for the values that standard carries.

+### Where a ground-fault function is furnished on a device that is not service equipment and no ground-fault function is furnished downstream of it, the study shall set the function's pickup and delay above the phase instantaneous clearing of every downstream device at the minimum line-to-ground fault current, so that a ground fault on a downstream circuit opens that circuit's device first.

+### A ground-fault relay at the service with no second level below it opens the whole building for a ground fault on any branch circuit that the branch breaker does not clear first, and the second level is what keeps a fault in one feeder inside that feeder. The service relay is set as slow and as high as the code allows for that reason, and the feeder relays are set inside the room it leaves. {note}

+### Where ground-fault protection is furnished on a system supplied by a generator or paralleled sources, the study shall verify the ground-fault coordination in each source case with the neutral grounding and the ground-fault sensing arrangement the equipment standards describe for that case.

+# Settings and Device Selections {toc}

+## Low-Voltage Trip Units {toc}

+### For every low-voltage circuit breaker with an adjustable trip unit, the study shall recommend a value for every adjustable function the trip unit carries, stated in the units and the steps the trip unit displays, including each of the following where the trip unit carries it:

+- the long-time pickup and the long-time delay, at the reference current the trip unit's curve family states

+- the short-time pickup, the short-time delay, and the I²t ramp in or out

+- the instantaneous pickup, or the instantaneous function off where the trip unit permits it and the coordination required calls for it, together with any instantaneous override the trip unit carries

+- the ground-fault pickup, the ground-fault delay, and the I²t ramp in or out

+- the restrained and unrestrained delays of a zone-selective interlock, and the function the interlock participates in

+- the setting the energy-reducing maintenance switch applies in its maintenance position

+### The study shall state the rating plug and the sensor rating each setting is referred to, and a setting that cannot be reached with the rating plug furnished shall be reported with the plug that reaches it, as an equipment change.

+### Recommendations of the form "as shipped", "factory setting", or "per manufacturer" shall not be accepted for any adjustable function, and a trip unit whose shipping settings happen to coordinate shall be recorded at those values as a recommended setting.

+### Where the trip unit furnished does not carry a function the coordination required depends on, including a short-time function where the pair above and below cannot otherwise be made selective, the study shall report the trip unit change on the equipment change list to the equipment standard that furnishes the breaker.

+## Protective Relays {toc}

+### For every protective relay within the study extent, the study shall recommend the setting of every enabled element, identified by its IEEE C37.2 device function number, in the units the relay accepts, and for every inverse-time overcurrent element shall state the pickup, the time dial or time multiplier, and the characteristic curve.

+### The inverse-time characteristic curves of the microprocessor relays shall be selected from the family indicated in the datasheet.

+```datasheet

+label: Relay Inverse-Time Curve Family

+type: select

+options:

+ - "IEEE C37.112 curves"

+ - "IEC 60255 curves"

+ - "Curves emulating the electromechanical relays elsewhere on the system"

+default: "IEEE C37.112 curves"

+```

+### The moderately, very, and extremely inverse curves of IEEE C37.112 are the shapes the North American fuses and electromechanical relays were drawn to, so a microprocessor relay set on them coordinates with the fuse below it and the utility relay above it on the same geometry, and they are the family nearly every study in this market uses; the IEC 60255 curves are the family of a system whose other relays, or whose Owner's engineering practice, are written to IEC, and their standard inverse is flatter than any IEEE curve at high current; a relay set to emulate the electromechanical relays elsewhere on a campus, where the relay offers that characteristic, lets one coordination sheet hold old and new relays on one shape, at the cost of a curve the next relay may not offer. {note}

+### The instantaneous element of a relay protecting a transformer primary shall be set above the transformer's inrush and above the maximum fault current on the secondary reflected to the primary, with a margin of not less than 25 percent on the reflected current and the DC offset the relay responds to, so that the element operates only for a fault between the relay and the transformer.

+### The instantaneous element of a relay protecting a feeder shall be set above the maximum fault current at the far end of the feeder, with the same margin, or shall be disabled where the feeder is short enough that no setting separates the near-end from the far-end fault, and the study shall record which was done.

+### Directional, differential, and distance elements shall be set from the current transformer ratios and accuracy classes, the impedances, and the zone boundaries the Engineer of Record's relaying scheme states, and the study shall plot the differential and pilot zones on the one-line diagram in the report so that the overcurrent settings are shown as the backup to them.

+### Where the relay furnished does not carry an element, a curve, or a setting range the coordination required depends on, the study shall report the relay change on the equipment change list to the equipment standard that furnishes the relay.

+## Fuses {toc}

+### Where an equipment standard leaves the ampere rating, the class, or the speed of a fuse to this study, the study shall select the fuse from the load current, the inrush or starting current it must carry, the damage curve it must clear beneath, and the selectivity ratio to the fuses above and below it, and shall deliver the selection to that equipment standard for the fuses it furnishes.

+### Where a fuse is the primary protection of a medium-voltage transformer or feeder, the study shall select the fuse's rating and type, E-rated for a transformer or feeder and R-rated for a motor circuit, with the minimum melting curve above the inrush or the starting current and the total clearing curve below the through-fault curve, the conductor damage curve, and the upstream device.

+### The settings record shall carry, against every fused position, the fuse class, speed, ampere rating, and interrupting rating the study selected, and the restriction to one manufacturer where selectivity rests on a ratio table.

+### A fuse has no setting, so the only thing the study can do with one is choose it, and the choice is made before the equipment is ordered or not at all. A fuse clipped in later because it was the one in stock is the most common way a coordinated system loses its coordination without a drawing changing. {note}

+## Coordination Deficiencies {toc}

+### Every pair of devices within the study extent that does not meet the criteria of this standard at every current at which both operate shall be listed in the report as a coordination deficiency, with the two devices by designation, the current range over which the pair does not coordinate, the operating case in which it occurs, the loads lost when the upstream device opens, and the remediation options available for it.

+### The study shall consider the following remediation options for each deficiency, as each applies:

+- a different setting on either device, where the criteria of this standard and the curves of the equipment permit it

+- a trip unit with a short-time function, a different rating plug, or a different sensor in the same frame

+- a different fuse class or speed in the same position

+- a current-limiting device downstream whose tested pair with the upstream device is covered by a selectivity table

+- zone-selective interlocking between the two devices, where both trip units support it

+- a different frame or a different device type in the position

+- acceptance of the deficiency by the Engineer of Record in writing, with the current range and the consequence recorded

+### No deficiency shall be accepted on a circuit the datasheet identifies under Circuits Requiring Selective Coordination.

+### Every accepted deficiency shall be accepted by the Engineer of Record in writing, and the acceptance shall state the current range, the loads lost, and the reason the remediation was not taken.

+### A deficiency between devices furnished as the contract documents specify, that the Engineer of Record declines to accept, shall be remediated as the Engineer of Record directs under the change provisions of the contract, and a deficiency that arises from a device the Contractor substituted for the one specified shall be remediated by the Contractor at no change in the contract sum.

+### Every device change the study requires shall be reported on the equipment change list before the device is released for manufacture where the study is delivered before equipment release, and a Contractor who releases a device before the study covering it is returned carries the cost of any change the study then requires.

+### Most real systems contain a pair that does not coordinate at some current, usually a main and a feeder whose instantaneous elements both see a bolted fault at the feeder's terminals, and the study is not a declaration that none exist. It is the list of where they are, how much current it takes to find one, and what it costs to remove it, so that the Engineer of Record decides with the numbers in hand rather than the Owner finding out at the first fault. {note}

+# Settings Record and Handoff {toc}

+## Settings Record Format {toc}

+### The study shall deliver the recommended settings in the formats indicated in the datasheet.

+```datasheet

+label: Settings Record Format

+type: checkbox

+options:

+ - "Consolidated settings table, one row per device"

+ - "Per-device settings sheet with as-found and as-left columns"

+ - "Settings files in the native format of each programmable relay and trip unit"

+default:

+ - "Consolidated settings table, one row per device"

+ - "Per-device settings sheet with as-found and as-left columns"

+constraint: all_of

+```

+### The consolidated table is what the Engineer of Record reads to see the system coordinate, and the per-device sheet is what the technician carries to the breaker and signs, so nearly every study delivers both; the native settings files are added where the relays and trip units are programmed by file rather than by keypad and the Owner wants the file that was loaded to be the file the engineer wrote, at the cost of the study engineer holding the configuration software of every make on the project. {note}

+### The consolidated settings table shall list every adjustable device and every fused position within the study extent by designation and location, every adjustable function with its recommended value in the units the device displays, the rating plug or sensor the value is referred to, the restrictions on make and type where selectivity rests on a table, and the curve sheet on which the setting is demonstrated.

+### Every per-device settings sheet shall identify the device by designation and location, shall list every adjustable function with its recommended value, and shall provide a column for the as-found value, a column for the as-left value, and a signature line for the party who applied the setting and the party who verified it.

+### Where native settings files are selected, each file shall be delivered with the relay or trip unit firmware version it was written for, and the recommended values in the file shall match the consolidated table, with the table governing where they differ.

+## Handoff to the Field {toc}

+### The reviewed study shall be furnished to the testing organization as the informational submittal [[sync/electrical-acceptance-testing]] requires, and no setting shall be applied to a device from a study that has not been reviewed and returned.

+### The settings shall be applied by the party the datasheet of [[sync/electrical-acceptance-testing]] selects and shall be verified under that standard, and this study shall not direct a different party to apply them.

+### Where the testing organization reports a device that cannot be set to the recommended value, the study engineer shall propose a revised setting for that device and for every device whose coordination depends on it within five working days, shall demonstrate the coordination at the revised value, and shall submit the revision to the Engineer of Record, who shall direct the setting to apply.

+### Where a setting is applied in the field at a value other than the study recommends and the Engineer of Record directs that it stand, the study engineer shall revise the curve sheets and the settings table to the as-left value and shall report any deficiency the as-left value creates.

+### The study is the only authority for a setting; the acceptance testing standard says so from the field's side, and this standard says so from the engineer's. The sheet the technician signs and the table the engineer sealed have to be the same numbers, and the five-day revision is what keeps a device that will not take its setting from being left at a value no one calculated. {note}

+## Handoff to the Arc-Flash Study {toc}

+### The final settings of every device within the study extent, with the clearing time of the device at the maximum and the minimum arcing current at each bus for every operating case, shall be furnished to the engineer performing the arc-flash study under [[sync/arc-flash-study]] on the day the study is returned, and again on the day any setting is revised.

+### The arc-flash study shall not be started on settings this study has not issued, and where a setting is revised after the arc-flash study has been performed on it, the Contractor shall not energize the equipment whose label rests on the superseded setting until the arc-flash study has been re-run.

+### An arc-flash label is a clearing time dressed as a number of calories, and the clearing time is a setting from this study. A label calculated on a design setting that the field never applied, or on a setting this study revised the week after, is wrong by exactly the difference, which is why the settings are issued to the arc-flash engineer as a dated deliverable and not read off a drawing. {note}

+# Study Report {toc}

+## Report Content {toc}

+### The study report shall contain the following, in a single sealed document with numbered pages:

+- a cover page with the project, the system studied, the study engineer, the date of issue, the revision history, and the seal and signature required under Study Engineer

+- an executive summary stating the study extent, the degree of coordination applied, the circuits requiring selective coordination and whether each was achieved, every coordination deficiency, and every equipment change required

+- the coordination criteria statement as returned, with the intervals, separations, bases, and priority applied

+- the one-line diagram of the short-circuit study, annotated with the designation of every device set and the curve sheet each appears on, and with the differential and pilot zones shown

+- the input data for every device set, giving the make, type, frame, sensor or rating plug, setting ranges, and curve reference, and for every curve plotted, its source

+- the utility's written request and response and the utility device characteristic

+- the curve sheets described under Curve Sheets

+- the consolidated settings table required under Settings Record Format

+- the deficiency list required under Coordination Deficiencies, with the remediation options and the acceptance of each accepted deficiency

+- the equipment change list

+- the selective coordination documentation for every circuit the datasheet identifies

+- the arc energy reduction documentation NFPA 70 240.87(A) requires, where the study set the method

+- the re-study trigger list

+- appendices holding the manufacturer curves, selectivity tables, decrement curves, and data sheets the settings rest on

+### The report shall be delivered in the formats the short-circuit study is delivered in under [[sync/short-circuit-study]], with the native model carrying the final settings.

+## Curve Sheets {toc}

+### Every device within the study extent shall appear on at least one curve sheet together with the device immediately upstream of it, and every sheet shall be plotted on logarithmic axes with current on the horizontal axis at a stated base voltage and time on the vertical axis, scaled so that every curve on the sheet is legible from its pickup to the maximum fault current plotted.

+### Every curve sheet shall show the following:

+- every device of the series pair or chain the sheet demonstrates, in distinct line styles, with the curve or the band drawn at the recommended setting and labeled with the device designation and the setting

+- the through-fault, damage, starting, thermal limit, decrement, and inrush curves and points that bound the settings on the sheet

+- a vertical marker at the maximum and the minimum fault current at each bus on the sheet, labeled with the bus, the case, and the value, as the short-circuit study calculated them

+- the coordination time interval or band separation measured at the point of closest approach between each pair, with the value

+- a title block identifying the sheet number, the buses, the base voltage, the operating case, the revision, and the date

+- a legend identifying every curve, band, point, and marker on the sheet

+### Where a pair is demonstrated by a selectivity table rather than by curves, the sheet shall carry a note naming the table, its revision, and the current up to which the pair is selective, at the point where the curves overlap.

+### Ground-fault coordination shall be plotted on separate sheets from phase coordination, and each operating case in which the settings differ shall be plotted on its own sheets.

+### A curve sheet is the argument for a setting, and a sheet that leaves off the fault current markers or the damage curves is a drawing of two curves that do not touch, which proves nothing about the system they are installed in. The reviewer reads the markers first. {note}

+# Study Revisions and Re-Study Triggers {toc}

+## Study Revisions Within the Project {toc}

+### The study engineer shall correct every error in a setting, a curve, or a table that is identified before the end of the project's correction period, and shall re-issue the affected sheets, the settings table, and the native model, at no cost to the Owner.

+### The study shall be revised whenever, after it is returned and before the equipment within the study extent is energized, the short-circuit study is revised, a device furnished departs from the device set in make, type, frame, trip unit, sensor, or rating plug, a fuse of a different class or rating is furnished, or a transformer, generator, or motor furnished departs from the one whose curve was plotted, and the revision shall re-plot every sheet the change affects.

+### A revision caused by a substitution or a change in the equipment furnished by the Contractor shall be made at the Contractor's cost, and a revision caused by a change in the utility's device, the design, or the short-circuit study's inputs shall be made as the Engineer of Record directs under the change provisions of the contract.

+### Every revision shall carry a revision number and date on the cover, a list of the settings that changed, and a statement of whether the arc-flash study needs to be re-run on it.

+## Re-Study Triggers {toc}

+### The report shall include a re-study trigger list, written for the Owner's operations staff, naming the events after which the Owner is to commission an updated coordination study before the affected portion of the system is returned to normal operation.

+### The re-study trigger list shall name at least the following events:

+- an updated short-circuit study under [[sync/short-circuit-study]], for any of the events that standard names

+- the replacement of a circuit breaker, trip unit, relay, or fuse with one of a different make, type, frame, class, or rating, including a replacement of either device of a pair whose selectivity rests on a tested table or a ratio table

+- a change to any setting the study recommends, for any reason

+- a firmware update to a relay or trip unit that changes its curve family or setting ranges

+- the addition, removal, or re-rating of a generator, an inverter-based source, or a UPS, or a change in the alternator of a generator

+- the addition of a motor at or above the individually modeled threshold, or of a transformer

+- a modification, addition, or replacement of any overcurrent device on an emergency, legally required standby, or critical operations power system, for which NFPA 70 700.32, 701.32, and 708.54 require the selective coordination to be re-evaluated

+- a change in the second level of ground-fault protection or in the neutral grounding of any source

+- notice from the utility of a change in its protective device or its settings

+- the five-year review of the arc-flash risk assessment under NFPA 70E 130.5(G), which rests on this study's settings

+### Where any trigger event occurs, the updated coordination study shall be followed by an updated arc-flash study under [[sync/arc-flash-study]] for the affected portion of the system, and the updated settings shall be applied and verified before the equipment is returned to normal operation.

+### The re-study trigger list shall be included in the operation and maintenance documentation of the electrical system, and the Owner's change procedures for the electrical system shall name the responsible engineer to be notified when a trigger event occurs.

+### Coordination is lost one device at a time, and almost never by a decision: a breaker replaced from stock with the same frame and a different trip unit, a fuse of the right amperage and the wrong speed, a relay firmware update that renamed the curve. None of them look like a reason to call an engineer, which is why the list is written in the words of the work rather than the words of the study. {note}

View current revision