1 Scope
NOTE This specification covers low-voltage, metal-enclosed, floor-standing motor control center (MCC) assemblies rated 600V and below. (1.1)
1.2 Equipment shall comply with NEMA ICS 18 and shall be listed and labeled to UL 845 by a Nationally Recognized Testing Laboratory (NRTL).
1.3 The assembly shall consist of one or more vertical sections joined to form a continuous assembly with a common horizontal bus and individual plug-in vertical buckets housing combination motor starters, feeder taps, soft starters, variable frequency drive units, control transformers, and metering as required.
NOTE A motor control center is distinguished from switchgear and switchboards by the integration of motor starting and protection devices into plug-in unit compartments that share a common bus structure. (1.4)
NOTE Where a single motor is served by an individually enclosed combination starter rather than a centralized assembly, an enclosed motor controller specification governs and an MCC is not required. (1.6)
NOTE This standard governs the MCC enclosure, bus structure, unit compartment construction, common control and metering, and field installation. (1.7)
1.8 The performance and configuration of variable frequency drive units installed as bucket contents shall comply with Hvac Variable Frequency Drives for HVAC service or with the applicable process control standard for other service. 2 Referenced Standards
2.1 Equipment, materials, and installation shall comply with the latest adopted edition of the following.
| Standard |
Title |
| UL 845 |
Standard for Motor Control Centers |
| UL 489 |
Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures |
| UL 508 |
Industrial Control Equipment |
| UL 61800-5-1 |
Adjustable Speed Electrical Power Drive Systems — Safety Requirements |
| NEMA ICS 18 |
Motor Control Centers |
| NEMA ICS 2 |
Industrial Control and Systems: Controllers, Contactors, and Overload Relays Rated Not More Than 2000 Volts AC or 750 Volts DC |
| NEMA ICS 6 |
Industrial Control and Systems: Enclosures |
| NEMA 250 |
Enclosures for Electrical Equipment (1000 Volts Maximum) |
| NFPA 70 |
National Electrical Code (Article 430 — Motors, Motor Circuits, and Controllers; Article 409 — Industrial Control Panels) |
| NFPA 70E |
Standard for Electrical Safety in the Workplace |
| IEEE 1584 |
Guide for Performing Arc-Flash Hazard Calculations |
| IEEE 519 |
Standard for Harmonic Control in Electric Power Systems |
| ANSI/NETA ATS |
Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems |
| IBC |
International Building Code (seismic provisions) |
| ASCE 7 |
Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
| ICC ES AC156 |
Acceptance Criteria for Seismic Certification by Shake-Table Testing of Nonstructural Components |
| ASHRAE 90.1 |
Energy Standard for Buildings Except Low-Rise Residential Buildings (submetering provisions) |
2.2 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.
3 Submittals
3.1 Action Submittals
3.1.1 Contractor shall submit the following for the Engineer's review and approval prior to fabrication:
- Shop drawings showing front, side, and rear elevations, overall dimensions, shipping splits, lifting points, and conduit entry locations
- Single line diagram showing horizontal and vertical bus configuration, main and feeder devices, and each motor circuit by unit designation
- Unit elevation drawings showing the arrangement of each bucket including starter type, branch device, control transformer, pilot devices, and nameplate
- Bill of materials listing every starter, branch circuit protective device, contactor, overload relay, soft starter, VFD unit, and metering device
- Schematic and wiring diagrams for the common control bus, communications network, and each unit
- Bus bracing calculations and short-circuit withstand documentation for the horizontal and vertical bus at the specified rating
- Combination motor controller series rating documentation, where series-rated combinations are proposed, identifying the upstream device required to achieve the marked rating
- Seismic certification documentation per ICC ES AC156 or analysis per ASCE 7, where required by the building code
- Harmonic distortion analysis where VFD or soft-start units exceed 25% of the connected MCC load, demonstrating compliance with IEEE 519 at the point of common coupling
☑ Shop drawings (front, side, rear elevations, shipping splits)
☐ Single line diagram with unit designations
☐ Unit elevation drawings (per bucket)
☐ Bill of materials with branch device and starter details
☐ Schematic and wiring diagrams (common control and per unit)
☐ Bus bracing and short-circuit withstand calculations
☐ Series-rating documentation (if applicable)
☐ Seismic certification (ICC ES AC156 or ASCE 7)
☐ Harmonic distortion analysis (IEEE 519)
☐ Catalog cut sheets for all branch devices, starters, and metering
☐ Manufacturer's standard nameplate schedule
3.1.2 Fabrication shall not proceed until submittals are reviewed and returned.
3.2 Closeout Submittals
3.2.1 Contractor shall provide at substantial completion:
- Operation and maintenance manuals, bound, with table of contents and section dividers for each unit type
- As-built shop drawings reflecting field modifications, including unit relocations and parameter changes
- Factory and field test reports including NETA acceptance test records and manufacturer startup reports
- Final programmed parameter settings for each VFD unit and soft-start unit, printed and provided in the manufacturer's electronic configuration file format
- Warranty documentation listing the MCC assembly serial number, individual unit serial numbers, installation dates, and warranty expiration dates
- Spare parts inventory with manufacturer part numbers and reorder information
- Complete set of keys for all locks and one set of breaker racking tools, where applicable
☑ Operation and maintenance manuals (bound, with section dividers)
☑ As-built shop drawings reflecting field modifications
☑ Factory and field test reports (NETA and manufacturer startup)
☐ Final programmed parameter settings (VFD and soft-start units)
☑ Warranty documentation (assembly and unit serial numbers)
☐ Spare parts inventory with part numbers and reorder information
☐ Complete set of keys and breaker racking tools (where applicable)
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1 MCCs shall be manufactured by a single company responsible for the structural assembly, horizontal and vertical bus, and all integral starter, branch device, and control components installed in factory-furnished units.
4.1.2 The manufacturer shall have a minimum of five years documented experience producing UL 845 listed motor control centers.
4.1.3 The manufacturer shall maintain an ISO 9001 certified quality management system.
4.1.4 The manufacturer shall maintain a service organization with factory-trained field representatives accessible within the project's geographic region.
4.1.5 The manufacturer shall commit to providing replacement plug-in units, bus components, and control devices for the MCC platform for a minimum of ten years from the date of manufacture.
4.2 Source Limitations
4.2.1 The MCC structure, horizontal bus, vertical bus, plug-in unit chassis, common control bus, and combination starter assemblies shall be furnished by the MCC manufacturer as an integrated assembly.
4.2.2 Third-party plug-in units, control components, or bus modifications assembled by others are not acceptable unless specifically pre-approved by the MCC manufacturer in writing and listed under the same UL 845 file.
4.2.3 Where VFD units, soft-start units, or metering devices furnished by others are installed in the MCC, those units shall be mounted in factory-furnished unit compartments meeting UL 845 unit construction requirements, and the assembly shall remain a single listed product.
4.3 Testing Personnel Qualifications
4.3.1 Field acceptance testing shall be performed by a firm regularly engaged in testing electrical power equipment, employing technicians certified by NETA or equivalent.
4.3.2 Testing personnel shall have a minimum of three years documented experience testing low-voltage motor control centers and the specific starter and drive technologies present in the assembly.
5 Environmental and Service Conditions
5.1 MCCs shall be suitable for continuous operation under the following ambient conditions.
NOTE Where site conditions exceed these parameters, notify the manufacturer and derate equipment accordingly. (5.2)
40°C (standard rating)
50°C (elevated mechanical room rating)
55°C (rooftop or unconditioned space)
Below 6,600 ft (2,000 m) - No derating
6,600 - 9,900 ft (2,000 - 3,000 m) - Derating required
Above 9,900 ft (3,000 m) - Consult manufacturer
C2 - Low (indoor, climate-controlled)
C3 - Medium (indoor, unconditioned mechanical room)
C4 - High (industrial, coastal, water/wastewater)
C5 - Very High (chemical, marine, severely corrosive)
5.3 Continuous current ratings of the horizontal bus, vertical bus, and individual starter units are established at the standard reference ambient of 40°C and below 6,600 ft altitude per NEMA ICS 18.
5.4 Where the installed environment exceeds these reference conditions, the manufacturer shall derate the assembly per published tables and confirm bus and unit ratings on the submittal documents.
5.5 For installations classified C3 or higher, vertical and horizontal bus shall be copper, tin-plated as a minimum.
5.6 For installations classified C3 or higher, exposed steel surfaces shall receive an enhanced two-coat finish system.
5.7 For installations classified C3 or higher, plug-in unit stab-on connectors shall be silver-plated.
5.8 For C5 environments, stainless steel enclosure construction or factory-applied chemical-resistant coatings shall be considered, and the manufacturer's certification of suitability for the specific corrosive exposure shall be submitted with shop drawings.
5.9 Seismic Requirements
5.9.1 Where required by the applicable building code, MCCs shall be seismically certified by shake-table testing per ICC ES AC156 or by analysis per ASCE 7.
Not required
IBC/ASCE 7 - Importance Factor 1.0
IBC/ASCE 7 - Importance Factor 1.5 (essential facility)
OSHPD pre-approval required (California healthcare)
5.9.2 Seismic certification shall be by an independent third-party testing laboratory.
5.9.3 Certification shall cover the complete assembly including all plug-in units, bus, and the largest configuration shipped to the site.
5.9.4 Certification of individual sections or components in isolation is not acceptable, and field-modified assemblies that depart from the certified configuration shall be re-evaluated.
6 Electrical Requirements
6.1 System Ratings
● No - Downstream Distribution (typical)
○ Yes - Main Service Entrance
208Y/120V 3-Phase 4-Wire
240V 3-Phase 3-Wire (delta)
480Y/277V 3-Phase 4-Wire
480V 3-Phase 3-Wire (delta)
600Y/347V 3-Phase 4-Wire
NOTE MCCs are typically downstream distribution equipment fed from upstream switchgear or switchboards. (6.1.1)
6.1.2 Where an MCC is configured as service entrance equipment, it shall comply with NFPA 70 Article 230 including provisions for service disconnect, available fault current marking, and ground fault protection as required by Article 230.95 for solidly grounded wye services of more than 150V to ground and 1000A or more.
6.2 Bus Rating
6.2.1 Main horizontal bus continuous current rating shall be as indicated on the one-line diagram. 6003000
600800100012001600200025003000
Default: 1200 A
Per drawings
22 kAIC
42 kAIC
65 kAIC
85 kAIC
100 kAIC
Type 1 - No damage to persons; component replacement acceptable
Type 2 - No damage permitted except light contact welding
● Fully rated (every device rated for available fault current)
○ Series rated (combinations tested per UL 489 / UL 845)
6.2.2 Bus shall be braced for the available short-circuit current at the point of installation as determined by a short-circuit analysis.
6.2.3 Coordinate the available fault current with the upstream device and the utility service per Low Voltage Switchgear. 6.2.4 Vertical bus rating shall be sized for the cumulative full-load current of the units installed in each vertical section with allowance for diversity.
6.2.5 Where high-density populations of large starters, soft starters, or VFD units are planned in a single vertical section, the 600 A standard rating is often insufficient and 800 A or 1200 A vertical bus shall be specified.
6.2.6 Verify vertical bus loading on the submittal documents.
6.2.7 The marked short-circuit current rating of the MCC shall equal or exceed the available fault current at the MCC line terminals.
NOTE The SCCR is the lowest of the bus bracing rating, the marked rating of each branch device, and the rating of any combination motor controller as listed in UL 508 / UL 845. (6.2.8)
NOTE Combination motor controllers using a magnetic-only branch device coordinated with a motor starter and overload relay establish a "Type 2" coordination rating per IEC 60947-4-1 that limits component damage during a fault; specify Type 2 coordination where post-fault uptime is critical. (6.2.9)
NOTE Series-rated combinations may reduce equipment cost but constrain future modifications because each downstream device is only rated when paired with the specific upstream device listed in the series rating table. (6.2.10)
NOTE Fully rated systems are recommended for facilities expected to undergo future load growth, equipment additions, or upstream source changes. (6.2.11)
6.3 Neutral and Ground Bus
Full rated (100% of main bus)
Reduced (50% of main bus)
Oversized (200% of main bus)
Not applicable (3-wire system)
● Included - Full length of assembly
○ Not required
6.3.1 Oversized neutral bus is required where nonlinear loads, including VFD units, electronic ballasts, and switched-mode power supplies served from the MCC, exceed 30% of the connected load.
6.3.2 The Engineer shall evaluate harmonic loading per IEEE 519 when selecting neutral bus sizing for MCCs serving substantial VFD populations.
6.3.3 Ground bus shall be bare copper, extending the full length of the assembly, accessible from the front of each vertical section without removing live parts barriers.
6.3.4 Every plug-in unit shall make positive ground continuity to the ground bus through a dedicated ground stab independent of the line stabs, engaging before the line stabs make contact during unit insertion.
6.3.5 Grounding electrode and equipment grounding conductor terminations shall comply with Grounding And Bonding. 7 Physical Construction
7.1 Enclosure
NEMA 1 - Indoor general purpose
NEMA 1A - Indoor general purpose, gasketed
NEMA 12 - Indoor industrial, dust-tight, drip-tight
NEMA 3R - Outdoor rainproof
NEMA 4 - Watertight (washdown areas)
NEMA 4X - Watertight, corrosion-resistant (food processing, water/wastewater)
Class I, Type B - Common control, wiring terminated at unit
Class I, Type C - Common control, wiring terminated at master terminal blocks (typical)
Class II, Type B - Manufacturer wires unit-to-unit per schematic, unit terminations
Class II, Type C - Manufacturer wires unit-to-unit per schematic, master terminal blocks
● Front accessible only (rear-against-wall)
○ Front and rear accessible
7.1.2 Enclosure shall be fabricated from cold-rolled steel with a minimum thickness of 12 gauge (2.66 mm) for structural members and 14 gauge (1.90 mm) for covers and doors.
7.1.3 All structural members shall be bolted or continuously welded.
7.1.4 Doors shall be hinged with concealed hinges and equipped with a quarter-turn latch for each non-defeatable interlocked unit and key-lockable latches for instrument and metering compartments.
7.1.5 For outdoor installations (NEMA 3R), the enclosure shall include rain hoods over ventilation openings, sun shields where direct solar exposure is expected, and thermostat-controlled condensation heaters in each vertical section sized at a minimum of 250 W per section.
7.1.6 Outdoor enclosures shall be furnished with a walk-in arrangement only where the MCC is large enough to provide working clearances per NFPA 70 Article 110.26 inside the enclosure; otherwise the enclosure shall be a non-walk-in design and working clearances shall be maintained externally.
NOTE NEMA ICS 18 defines Class I MCCs as assemblies where the manufacturer makes no electrical interconnections between units beyond the common bus, leaving inter-unit logic wiring to the field installer. (7.1.7)
NOTE Class II MCCs include factory-installed inter-unit control wiring per a customer-furnished elementary diagram and are appropriate for projects with extensive interlocking, sequencing, or PLC integration. (7.1.8)
NOTE Type B wiring terminates control conductors at the individual unit's terminal block; Type C extends control conductors to a master terminal block at the top or bottom of each vertical section for simplified field termination. (7.1.9)
NOTE Class I Type C is the most common configuration in commercial and institutional service. (7.1.10)
7.1.11 Rear-accessible configurations require minimum 36 in. working clearance at rear per NFPA 70 Article 110.26 and provide front and rear access to bus, cable, and unit compartments.
NOTE Front-accessible configurations may be installed with the rear of the assembly against a wall and reduce required floor space at the cost of rear maintenance access. (7.1.12)
7.2 Bus Bars
● Copper (tin-plated)
○ Copper (silver-plated)
○ Aluminum (tin-plated)
● Copper (tin-plated)
○ Copper (silver-plated)
○ No future extension
● Provision for future extension at one end
○ Provision for future extension at both ends
7.2.1 Vertical bus shall be copper regardless of horizontal bus selection because vertical bus is repeatedly stressed by unit insertion and removal.
7.2.2 Aluminum vertical bus is not acceptable.
7.2.3 Bus bar joints shall be bolted with Belleville washers to maintain contact pressure under thermal cycling, and all joint contact surfaces shall be plated to match the bus plating.
7.2.4 Vertical bus shall be isolated and insulated from the unit compartment interior.
7.2.5 Bus shall be covered with a flame-retardant insulating shield that exposes only the stab openings required by the inserted unit at each elevation.
7.2.6 Open stab openings not occupied by a plug-in unit shall be covered with manufacturer-furnished blanking shutters.
7.3 Wireway
● Top entry
○ Bottom entry
○ Top and bottom entry
7.3.1 Each vertical section shall include a continuous vertical wireway adjacent to the unit compartments with a hinged or removable cover providing access to the full height of the section.
7.3.2 Vertical wireway shall be sized to accept all load and control conductors entering and leaving the section without exceeding NFPA 70 Article 312 fill limits, and shall be physically separated from the bus compartment by a continuous metal barrier.
7.3.3 A continuous horizontal wireway shall be provided at the top of the assembly, the bottom of the assembly, or both, sized for the cumulative conduit and conductor entries to the assembly.
7.3.4 Top-entry, bottom-entry, or both shall be available as required by the field conduit layout.
7.4 Barriers and Compartmentalization
7.4.1 Metal barriers shall separate the horizontal bus compartment, the vertical bus compartment, the unit compartments, and the wireway.
7.4.2 Barriers shall prevent propagation of an arcing fault from one compartment to adjacent compartments.
7.4.3 Each plug-in unit shall be installed in an individual compartment with a hinged door interlocked to the unit's branch disconnect such that the door cannot be opened with the disconnect in the ON position unless the interlock is defeated by a tool.
7.5 Arc Flash Mitigation
Not required
Maintenance switch on main and feeders 1200A and above (NEC 240.87)
Zone-selective interlocking (ZSI) on electronic trip devices
Arc-resistant construction tested per IEEE C37.20.7
NOTE NFPA 70 Article 240.87 requires arc energy reduction on circuit breakers rated 1200A or more. (7.5.1)
7.5.2 For MCC main breakers and feeder breakers meeting the 1200A threshold, an Energy Reducing Maintenance Switch (ERMS) or equivalent reduction method shall be provided.
7.5.3 Arc flash hazard analysis shall be performed per IEEE 1584 and incidence energy labels shall be applied to every door and access location per NFPA 70 Article 110.16 and NFPA 70E.
7.6 Infrared Scanning Provisions
7.6.1 Enclosure shall include removable infrared inspection windows or cover plates at each main bus joint, each vertical bus stab tier, and the main incoming lugs.
7.6.2 Windows shall allow thermographic inspection of energized connections without removing live-parts barriers.
8 Plug-In Unit Construction
8.1 Unit Sizes
● Plug-in (stab-on) units
○ Frame-mounted (bolt-on) units for largest frames only
○ Mixed - Plug-in below specified frame, frame-mounted above
8.1.1 Plug-in unit compartments shall be sized in standard NEMA ICS 18 increments to permit interchange of units of equal size between compartments.
8.1.2 Sixth-, quarter-, half-, three-quarter-, and full-section unit heights shall be available.
8.1.3 Each compartment shall be furnished with a separately operable hinged door with a viewing window where pilot devices are mounted.
8.1.4 Plug-in units engage the vertical bus through self-aligning stab connectors and engage the ground bus through an independent ground stab that makes before and breaks after the line stabs.
NOTE Frame-mounted units are used for the largest motor starter frames (typically NEMA Size 5 and above) and for VFD units exceeding the largest plug-in compartment dimension; frame-mounted units are bolted to the assembly structure and field-wired to the bus. (8.1.5)
8.2 Combination Motor Starters
Motor circuit protector (magnetic-only circuit breaker) - typical
Thermal-magnetic molded case circuit breaker
Fusible disconnect switch
Full-voltage non-reversing (FVNR) - typical
Full-voltage reversing (FVR)
Two-speed (constant or variable torque)
Reduced voltage soft starter (RVSS)
Variable frequency drive (VFD)
Wye-delta (closed transition)
Autotransformer reduced voltage
Size 1 (up to 10 HP at 480V)
Size 2 (up to 25 HP at 480V)
Size 3 (up to 50 HP at 480V)
Size 4 (up to 100 HP at 480V)
Size 5 (up to 200 HP at 480V)
Size 6 (up to 400 HP at 480V)
● Electronic (solid-state) with class selection
○ Bimetallic thermal
120V AC from unit-mounted control transformer (typical)
24V DC from common DC control bus
Line voltage (240V, 480V) - no transformer
8.2.1 Combination motor starters shall comply with NEMA ICS 2 and UL 845.
8.2.2 Each combination starter unit shall consist of an integral branch disconnect, a magnetic motor contactor, an overload relay, control transformer (where required), and pilot devices, assembled and wired by the manufacturer in a single plug-in compartment.
NOTE Motor circuit protectors (MCPs) are magnetic-only breakers sized for short-circuit and ground-fault protection of the motor branch circuit while the overload relay provides running overload protection per NFPA 70 Article 430. (8.2.3)
NOTE MCPs are preferred for combination starters because the magnetic-only design allows trip setting coordination with motor inrush characteristics. (8.2.4)
NOTE Thermal-magnetic breakers are acceptable where MCPs are unavailable for the required frame size, and fusible switches are appropriate where high interrupting capacity is required without breaker upgrade. (8.2.5)
NOTE Full-voltage non-reversing is the most common configuration for HVAC fans and pumps not requiring reduced-voltage starting or variable speed control. (8.2.6)
8.2.7 Reduced voltage soft starters and VFDs are required for motors where in-rush current exceeds utility or generator source capacity, where mechanical shock loading must be reduced, or where variable speed control is required for process or energy conservation.
8.2.8 Selection of soft starter versus VFD shall be based on whether continuous speed control is required (VFD) or only controlled starting and stopping (soft starter).
8.2.9 Individual starter sizes for each motor shall be selected by the manufacturer based on the connected motor horsepower and service factor with no derating below NEMA ICS 2 published ratings.
8.2.10 IEC-rated contactors shall not be substituted for NEMA-rated contactors except where specifically approved by the Engineer.
NOTE IEC contactors generally have lower thermal mass and shorter expected mechanical life under high-cycle service. (8.2.11)
NOTE Electronic overload relays provide selectable trip class (Class 10, 20, or 30) to match motor starting characteristics, ground fault sensing, phase loss and phase imbalance protection, and communications interfaces for status and trip reporting. (8.2.12)
NOTE Bimetallic thermal overloads are acceptable for small simple FVNR starters where the additional functionality of electronic relays is not required. (8.2.13)
8.2.14 Unit-mounted control transformers shall be sized for the connected pilot device load plus 50% spare capacity, with primary and secondary fusing per NFPA 70 Article 450.
8.2.15 Common 24V DC control buses are preferred where the MCC integrates with a PLC or DCS using 24V DC field devices; coordinate the control voltage selection with Building Automation System or the process control standard. 8.3 Variable Frequency Drive Units
● No bypass
○ Manual bypass (across-the-line, manual transfer)
○ Automatic bypass on drive fault (across-the-line, automatic transfer)
8.3.1 VFD units installed in MCC plug-in compartments shall comply with UL 61800-5-1 and shall be mounted, wired, and cooled within the compartment per the drive manufacturer's published requirements.
8.3.2 Compartment ventilation shall accommodate the drive's continuous heat dissipation at full load and ambient.
8.3.3 Where the drive heat dissipation exceeds the compartment's natural ventilation capacity, a forced-air cooled compartment or a frame-mounted drive shall be specified.
NOTE VFD bypass adds an across-the-line starter and contactor arrangement that can run the motor at full speed if the drive fails. (8.3.5)
NOTE Bypass is recommended for life-safety and essential service motors (smoke control fans, critical pumps) but is not necessary for general HVAC service where temporary motor outages during drive repair are acceptable. (8.3.6)
NOTE Bypass increases the unit size by approximately one size and adds cost; coordinate the requirement with the building operations plan. (8.3.7)
8.4 Soft Starter Units
Solid-state (SCR-based) with electronic ramp
Solid-state with bypass contactor (energized at full speed)
NOTE Solid-state soft starters with run bypass contactors are preferred for motors above 25 HP because the bypass contactor carries the running current after the motor reaches full speed, eliminating SCR heat dissipation at steady state and extending equipment life. (8.4.1)
NOTE Soft starters without bypass dissipate continuous heat through the SCRs and are limited to lower HP applications or duty cycles. (8.4.2)
8.5 Metering Units
No metering
Main incoming metering only
Main and feeder metering
Main and per-motor metering
☑ Voltage (L-L, L-N all phases)
☐ Current (per phase)
☐ Power factor (per phase and total)
☐ kW / kVA / kVAR (demand and instantaneous)
☐ kWh / kVARh energy accumulation
☐ Harmonics (THD per phase, individual to 31st)
☐ Min/max recording with time stamp
☐ Waveform capture (on event)
8.5.1 Where building energy code requires submetering of motor loads (ASHRAE 90.1 Section 8.4.3 or local amendments), kWh accumulation shall be a minimum required function and shall be accessible to the building automation system.
NOTE Per-motor metering supports mechanical system commissioning, fault detection and diagnostics, and ongoing energy verification but adds material cost and is appropriate only for the largest motors and for facilities with measurement and verification programs in place. (8.5.2)
9 Common Control and Communications
9.1 Common Control Bus
9.1.1 Where Class I or Class II Type C wiring is specified, the assembly shall include a common control bus consisting of master terminal blocks at the top or bottom of each vertical section, with all unit-to-unit control conductors terminated at the master terminal blocks for field cross-connection.
9.1.2 Master terminal blocks shall be permanently identified with conductor designations matching the schematic diagrams.
9.2 Communications Network
No communications
Modbus RTU (RS-485 daisy-chain)
Modbus TCP/IP (Ethernet)
EtherNet/IP
PROFINET
PROFIBUS-DP
DeviceNet
● Single network (all devices on one segment)
○ Segmented (drives/metering on separate segment from starters)
○ Redundant ring (managed switches with ring protocols)
9.2.1 Where a communications network is specified, every electronic overload relay, soft starter, VFD unit, and metering device shall be furnished with a network interface compatible with the selected protocol.
9.2.2 Network cabling, switches (for Ethernet protocols), and termination components shall be furnished within the MCC enclosure.
9.2.3 Network address assignments shall be documented on the submittal documents and updated on the as-built drawings.
NOTE For Ethernet-based protocols, redundant ring topologies using managed switches with rapid spanning tree or DLR (Device Level Ring) are appropriate for facilities where loss of motor status visibility would interrupt critical operations. (9.2.4)
NOTE For typical commercial HVAC service, a single network with unmanaged switches is sufficient. (9.2.5)
9.2.6 Coordinate the communications network design with Building Automation System and with the building's overall converged network architecture. 10 Finish and Identification
10.1 Enclosure shall receive a minimum two-coat paint system: corrosion-resistant primer and manufacturer's standard polyester powder coat finish.
10.2 Minimum total dry film thickness shall be 3 mils (75 microns).
10.3 For installations classified C3 or higher, an enhanced paint system with a minimum 5 mils dry film thickness shall be applied.
10.4 Labeling
10.4.1 Manufacturer shall provide engraved phenolic nameplates for the MCC assembly, each vertical section, and each plug-in unit.
10.4.2 Nameplates shall identify:
- MCC designation and one-line reference
- Bus ratings (voltage, continuous current, short-circuit current rating)
- Unit designation matching the one-line diagram and motor schedule
- Connected motor designation, horsepower, full-load amps, and service
- Branch device frame size and trip rating
- Arc flash warning labels per NFPA 70E and IEEE 1584
● Laminated phenolic (indoor)
○ Stainless steel (outdoor or corrosive)
○ Aluminum (anodized)
10.4.3 Unit designations and connected motor designations shall match the labels installed at each motor and at each disconnect switch downstream of the MCC, supporting trouble-shooting and lockout/tagout procedures.
11 Testing
11.1 Factory Tests
11.1.1 The manufacturer shall perform the following production tests on the completed MCC assembly per UL 845 and NEMA ICS 18:
- 60 Hz dielectric withstand test on horizontal and vertical bus
- Insulation resistance measurement on each phase bus and the neutral bus
- Mechanical operation of each plug-in unit (insertion, removal, door interlock)
- Functional test of each combination starter (manual close/open, overload trip simulation)
- Functional test of each VFD and soft-start unit per the device manufacturer's test specification
- Current transformer ratio and polarity test (where CTs are installed)
- Control wiring continuity verification against the as-built schematics
- Communications network point-to-point continuity (where networks are installed)
- Visual and dimensional inspection
○ Witnessed by Owner's representative
● Unwitnessed with certified test report
○ Not required beyond standard production tests
11.1.2 Where witnessed factory testing is specified, the manufacturer shall provide a minimum of two weeks advance notice of test readiness.
11.1.3 Test procedures shall be submitted for review prior to testing.
11.2 Field Acceptance Tests
11.2.1 Contractor shall engage a qualified independent testing firm to perform acceptance testing per NETA ATS Section 7.16 (Motor Control Centers).
11.2.2 Testing shall occur after installation is complete and before the equipment is energized.
● NETA acceptance testing and manufacturer startup
○ NETA acceptance testing only
○ Manufacturer startup only
11.2.3 Field acceptance tests shall include as a minimum:
- Visual and mechanical inspection of all sections and units
- Insulation resistance testing of horizontal and vertical bus (phase-to-phase and phase-to-ground)
- Contact resistance measurement on all bolted bus connections
- Plug-in unit insertion and withdrawal verification on every compartment
- Overload relay primary current injection at one trip setpoint per relay
- Branch device functional test (manual operation, trip indication)
- VFD and soft-start unit commissioning per the device manufacturer's startup procedure
- Communications network functional verification (every connected device responds at its address)
- Ground continuity measurement from each unit compartment ground stab to the ground bus
- Functional testing of all interlocks, alarms, and remote control points
● Initial scan within 90 days of energization, follow-up at 11 months
○ Initial scan within 90 days of energization only
○ Not required
11.2.4 Infrared scanning shall be performed under normal operating load conditions (minimum 40% of rated load on each scanned circuit).
11.2.5 All connections exceeding 10°C rise above ambient shall be reported and corrected.
NOTE Follow-up scan at 11 months captures connections that may loosen during the initial thermal cycling period and is recommended for all MCCs serving critical loads. (11.2.6)
12 Installation
12.1 Concrete Housekeeping Pad
12.1.3 MCCs shall be mounted on a reinforced concrete housekeeping pad extending a minimum of 3 in. beyond the base of the assembly on all sides.
12.1.4 Pad shall be a minimum of 4 in. above finished floor for indoor installations and 6 in. above finished grade for outdoor installations.
12.1.5 Coordinate pad dimensions, conduit penetrations, and anchor bolt locations with equipment shop drawings prior to concrete placement.
12.2 Equipment Setting
NOTE After assembly, and before energizing, verify the following: (12.2.1)
- All shipping restraints and temporary grounds removed
- Horizontal and vertical bus joint torque verified per the manufacturer's specifications using a calibrated torque wrench
- All plug-in units rack and operate freely with positive ground stab engagement
- Conduit terminations sealed and cable terminations torqued to the manufacturer's specifications
- Space heaters energized (outdoor or unconditioned installations)
- Working clearances per NFPA 70 Article 110.26 are maintained
12.2.2 Contractor shall comply with the manufacturer's installation instructions and applicable rigging requirements.
12.2.3 Remove all temporary shipping braces, blocking, and desiccants prior to final assembly.
12.2.4 Verify section alignment and bolt all sections together per the manufacturer's torque specifications.
12.2.5 Make horizontal bus splice connections at each shipping split per the manufacturer's procedure using calibrated torque tools.
12.3 Wiring and Terminations
12.3.1 Power and control conductors entering and leaving the MCC shall comply with Conductors And Cables. 12.3.2 Conduit entries to the MCC shall comply with Raceways And Conduit and shall enter the assembly only through the wireway areas designated by the manufacturer; entries through bus compartments, unit compartments, or barrier walls are prohibited. 12.3.3 Terminations at unit terminal blocks shall be torqued to the device manufacturer's published specifications using a calibrated torque tool, and torque application shall be documented for ground, line, and load terminations.
12.3.4 Wire labels at each unit shall match the schematic conductor designations.
12.4 Working Clearance
12.4.1 Minimum working space shall be maintained per NFPA 70 Article 110.26 based on the nominal voltage and accessibility configuration:
| Voltage |
Condition 1 (exposed on one side) |
Condition 2 (exposed on both sides) |
| 0-150V |
36 in. |
36 in. |
| 151-600V |
36 in. |
48 in. |
12.4.2 Working space shall not be used for storage.
12.4.3 Dedicated electrical space above the assembly per NFPA 70 Article 110.26(E) shall be maintained free of foreign systems including piping, ductwork, and structure not associated with the MCC.
13 Delivery, Storage, and Handling
13.1 MCCs shall be shipped in the largest factory-assembled sections that can be transported to and within the installation site.
13.2 Verify all pathway dimensions (doors, hallways, elevator shafts) between the delivery point and the final installation location prior to ordering, and coordinate shipping splits on the shop drawings.
13.3 Equipment shall be stored indoors in a clean, dry, climate-controlled location.
13.4 Where indoor climate-controlled storage is not available, the manufacturer shall provide weatherproof packaging and condensation heaters shall be connected and energized during storage if the storage period exceeds 30 days or if the storage environment is not climate-controlled.
13.5 Plug-in units shall remain in their factory-installed compartments during shipment and storage and shall not be removed until field acceptance testing.
14 Warranty
1 year from substantial completion
2 years from substantial completion
3 years from substantial completion
5 years from substantial completion
☑ Parts only
☐ Parts and labor
☐ Emergency response (24/7 with 4-hour commitment)
☐ Scheduled preventive maintenance (annual)
14.1 Warranty shall cover defects in materials and workmanship under normal use and service conditions, including the MCC structure, bus, all factory-installed plug-in units, and integral control devices.
14.2 The manufacturer shall maintain a service organization capable of providing emergency replacement plug-in units and field service within 24 hours during the warranty period.
15 Spare Parts
☑ One spare unit of each FVNR starter size installed
☐ One spare unit of each FVR starter size installed
☐ One spare VFD unit of largest size installed
☐ One spare soft-start unit of largest size installed
☐ One spare overload relay of each rating installed
☐ One spare control transformer of each rating installed
☐ 10% spare blank unit compartments (minimum one per section)
15.1 Manufacturer shall provide the following additional spare parts:
- One set of replacement fuses for each fuse type and rating installed in the assembly
- One set of replacement indicating lights and lenses for each pilot device type installed
- One set of replacement push-button operators and selector switches for each type installed
- One set of unit-extraction handles, blanking shutters, and the manufacturer's standard tool kit for unit removal and reinstallation
- One complete set of keys for all locks
15.2 Spare plug-in units shall be of the same type, rating, and configuration as the installed units and shall be fully interchangeable.
15.3 Spare units shall be stored in a manufacturer-provided storage cabinet or on shelving in the electrical room or motor control room, organized and labeled by unit designation.