−---
−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
−
−This specification covers the preparation, documentation, and acceptance of a protective device coordination study for the project's electrical distribution system. The study shall demonstrate, by time-current curve analysis, that the overcurrent protective devices installed in the system operate selectively — the device immediately upstream of a fault opens first and the remainder of the system stays energized — over the full range of available fault currents and overload conditions.
−
−A coordination study is not a stand-alone analysis. It is the middle study in a three-study sequence: the short-circuit study establishes the 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. The Contractor shall not begin the coordination study until the short-circuit study is complete and accepted, and shall not begin the arc-flash study until the coordination study is complete and accepted. See [[sync/short-circuit-study]] and [[sync/arc-flash-study]].
−
−This standard applies 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 is 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, or the architecture of differential and pilot schemes is engineered upstream of the study by the Engineer of Record. The study uses the as-designed scheme and produces settings for it.
−
−# Referenced Standards
−
−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.
−
−| 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
−
−## Action Submittals
−
−Contractor shall submit the following for the Engineer's review and acceptance. Field commissioning of relay and breaker settings shall not proceed until the coordination study is accepted in writing.
−
−- 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"
−```
−
−## Closeout Submittals
−
−Contractor shall provide 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
−
−# Quality Assurance
−
−## Engineer of Record for the Study
−
−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.
−
−```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
−
−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 are not acceptable for the action submittal because they cannot be verified against published device characteristics.
−
−```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"
−```
−
−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.
−
−## Independence
−
−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.
−
−```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
−
−The coordination criteria are the rules the study uses to decide whether two devices in series coordinate. These criteria shall be stated in the study report so that the basis for every conclusion is auditable.
−
−## Coordination Time Interval
−
−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. 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.
−
−```datasheet
−label: Minimum CTI — Electromechanical Relays Upstream
−type: range
−unit: seconds
−options:
− min: 0.25
− max: 0.50
− setpoints: [0.30, 0.35, 0.40, 0.50]
−default: 0.40
−```
−
−```datasheet
−label: Minimum CTI — Microprocessor (Static) Relays Upstream
−type: range
−unit: seconds
−options:
− min: 0.15
− max: 0.40
− setpoints: [0.20, 0.25, 0.30, 0.40]
−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: [0.10, 0.15, 0.20, 0.30]
−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. 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
−
−```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. Partial selectivity is acceptable for general distribution 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, is 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
−
−The selective-coordination requirement does 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).
−
−```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 — coordination is preserved by the interlock signal itself. Energy-reducing maintenance switches reduce clearing time at the operator's command during maintenance and 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. 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
−
−The coordination study cannot proceed without complete and verified input data. 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
−
−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.
−
−```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
−
−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
−
−The study shall use the actual nameplate and curve data of the equipment installed on the project, not generic or assumed values. Required data includes:
−
−- 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
−
−```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 is acceptable for the action submittal so that ordering and installation are not delayed, but 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.
−
−## One-Line Diagram
−
−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
−
−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. The study shall analyze, at minimum, the coordination pairs listed below.
−
−## Coordination Pairs Analyzed
−
−```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 (see below), 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
−
−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; this is a coordination requirement with equipment, not a coordination requirement between two devices, but it shall be demonstrated on the same plot.
−
−```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
−
−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.
−
−```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.
−
−## Conductor Damage Curves
−
−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.
−
−```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 and shall be used in preference to manufacturer-specific curves except where the cable manufacturer publishes a more restrictive curve.
−
−## Ground-Fault Coordination
−
−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.
−
−```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. Coordination of downstream ground-fault devices with the service main shall respect that ceiling.
−
−# Settings Recommendations
−
−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" are not acceptable for adjustable devices.
−
−## Low-Voltage Breaker Trip Unit Settings
−
−For every low-voltage breaker with an electronic trip unit, the study shall recommend:
−
−- 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; the consolidated table is what the Engineer reviews for system-wide selectivity. Producing both is recommended.
−
−## Protective Relay Settings
−
−For every microprocessor or electromechanical relay, the study shall recommend the setting for each enabled element. For overcurrent elements this includes 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
−
−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
−
−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.
−
−```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
−
−A real system frequently contains a coordination pair that does not coordinate at every credible fault current. The study shall not pretend otherwise. 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. Common compromises include:
−
−- 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.
−
−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
−
−## NEC 700.27 — Emergency Systems
−
−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. Partial coordination, time-based coordination above a current threshold, and series-rated combinations that do not maintain selectivity are not acceptable for the emergency branch.
−
−```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
−
−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, applies to the legally required standby branch in the same manner as to the emergency branch.
−
−```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
−
−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.
−
−```datasheet
−label: Critical Operations Power System (NEC 708) Present
−type: radio
−options:
− - "Yes"
− - "No"
−default: "No"
−```
−
−## Healthcare Essential Electrical Systems
−
−For healthcare facilities the essential electrical system per NFPA 99 and NEC Article 517 imposes additional reliability and selective-coordination considerations. Where the project includes a healthcare essential electrical system, coordination shall additionally satisfy NFPA 99 and the requirements of [[sync/healthcare-essential-electrical-systems]].
−
−```datasheet
−label: Healthcare Essential Electrical System Present
−type: radio
−options:
− - "Yes — coordinate with healthcare standard"
− - "No"
−default: "No"
−```
−
−## Fire Pump Circuits
−
−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
−
−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
−
−```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
−
−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:
−
−- 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
−
−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 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.
−
−Settings table is [[drawing: per the protective device settings schedule]].
−
−## Per-Device Settings Sheets
−
−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 — it shall not require cross-reference to other parts of the report.
−
−# Re-Study Triggers
−
−The protective device coordination study reflects the system as designed and as commissioned. 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 such a list, written for the Owner's operations staff in non-engineering language. At a minimum, the re-study trigger list shall include the following events:
−
−```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 this 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
−
−Coordination study work intersects with several other electrical and project scopes. 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 | 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
+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: [0.30, 0.35, 0.40, 0.50]
+default: 0.40
+```
+
+```datasheet
+label: Minimum CTI — Microprocessor (Static) Relays Upstream
+type: range
+unit: seconds
+options:
+ min: 0.15
+ max: 0.40
+ setpoints: [0.20, 0.25, 0.30, 0.40]
+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: [0.10, 0.15, 0.20, 0.30]
+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
+
+```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"
+```
+
+### The study shall use the actual nameplate and curve data of the equipment installed on the project, not generic or assumed values.
+
+### 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 |