1 Scope
NOTE This standard governs the design and construction of dedicated electrical rooms and closets — the rooms that house service entrance equipment, distribution switchgear, switchboards, panelboards, motor control centers, dry-type transformers, automatic transfer switches, indoor standby generators or paralleling switchgear, DC battery systems, and the raceway, grounding, and control infrastructure that connects them. (1.1)
NOTE The electrical room is not a piece of equipment; it is the envelope, the working environment, and the access regime that allow the equipment inside it to be installed safely, maintained safely, and operated for its full service life. (1.2)
NOTE The room is regulated by two overlapping bodies of code. (1.3)
NOTE NFPA 70 (the National Electrical Code) sets the working space, dedicated equipment space, egress, illumination, and access requirements that apply to the equipment as installed, principally in Article 110.26 for installations 1000 V and below and in Articles 110.31 through 110.34 for installations over 1000 V. The International Building Code sets the fire-resistance ratings, occupancy classification, structural support, and means-of-egress requirements that apply to the room as a building element, principally in Chapters 5 through 10 and in Section 304 for utility occupancy. (1.4)
1.5 Where the contract documents, the adopted building code, the adopted electrical code, or a referenced standard impose differing requirements, the more stringent shall govern unless the Engineer of Record directs otherwise in writing.
1.6 The Contractor and the design team shall treat this standard as setting the room conditions that the equipment specifications assume.
1.9 Wall, floor, and ceiling penetrations shall be sealed per Firestopping; the rated assemblies themselves are constructed under separate scopes coordinated with this standard. 1.12 Telecommunications equipment shall not be housed in an electrical room governed by this standard except where specifically coordinated with Telecommunications Bonding. NOTE The telecommunications and electrical scopes have incompatible grounding and access requirements when intermixed casually. (1.13)
NOTE This standard does not address exterior pad-mounted equipment, utility-owned vaults, generator yards, fuel rooms, or liquid-immersed transformer vaults under NEC 450.42; those scopes are governed by their own standards and codes. (1.14)
2 Referenced Standards
2.1 Equipment, room construction, and installation shall comply with the latest adopted edition of the following.
| Standard |
Title |
| NFPA 70 |
National Electrical Code — Article 110.26 (Spaces About Electrical Equipment, 1000 V and below) |
| NFPA 70 |
National Electrical Code — Article 110.27 (Guarding of Live Parts) |
| NFPA 70 |
National Electrical Code — Article 110.31 (Enclosure for Electrical Installations, over 1000 V) |
| NFPA 70 |
National Electrical Code — Article 110.34 (Working Space, over 1000 V) |
| NFPA 70 |
National Electrical Code — Article 110.16 (Arc-Flash Hazard Warning) |
| NFPA 70 |
National Electrical Code — Article 210.63 (Receptacle in Service-Equipment Rooms) |
| NFPA 70 |
National Electrical Code — Article 240.24 (Location of Overcurrent Devices) |
| NFPA 70 |
National Electrical Code — Article 250 (Grounding and Bonding) |
| NFPA 70 |
National Electrical Code — Article 450.21 (Indoor Dry-Type Transformer Installation) |
| NFPA 70 |
National Electrical Code — Article 450.42 (Indoor Vault for Liquid-Insulated Transformers) |
| NFPA 70E |
Standard for Electrical Safety in the Workplace |
| NFPA 75 |
Standard for the Fire Protection of Information Technology Equipment (where adjacent IT space governs) |
| NFPA 101 |
Life Safety Code (egress from electrical rooms, door swing, panic hardware) |
| IBC |
International Building Code, Chapter 3 — Use and Occupancy Classification (Section 304, Business; utility classification where applicable) |
| IBC |
International Building Code, Chapter 7 — Fire and Smoke Protection Features |
| IBC |
International Building Code, Chapter 10 — Means of Egress |
| ASTM E119 |
Standard Test Methods for Fire Tests of Building Construction and Materials |
| UL 263 |
Fire Tests of Building Construction and Materials |
| ASHRAE 90.1 |
Energy Standard for Buildings (lighting power density, ventilation energy) |
| IECC |
International Energy Conservation Code (lighting and envelope) |
| IEEE 484 |
Recommended Practice for Installation Design and Installation of Vented Lead-Acid Batteries for Stationary Applications |
| IEEE 1187 |
Recommended Practice for Installation Design and Installation of Valve-Regulated Lead-Acid Batteries for Stationary Applications |
| IEEE 1584 |
Guide for Performing Arc-Flash Hazard Calculations |
| NEMA 250 |
Enclosures for Electrical Equipment (1000 V Maximum) |
| ICC A117.1 |
Accessible and Usable Buildings and Facilities (where electrical rooms are publicly accessed) |
| ASCE 7 |
Minimum Design Loads and Associated Criteria for Buildings (seismic anchorage) |
| ICC ES AC156 |
Acceptance Criteria for Seismic Certification by Shake-Table Testing |
| ANSI/NETA ATS |
Acceptance Testing Specifications for Electrical Power Equipment and Systems |
3 Submittals
3.1 Action Submittals
3.1.1 The Contractor shall submit the following for the Engineer's and Architect's review prior to construction of the room and prior to procurement of room-specific products such as doors, hardware, ventilation equipment, and security devices.
- Room layout drawings showing every equipment line-up, the required NEC 110.26 or 110.34 working space envelope around each equipment face, dedicated equipment space above and below each line-up, door swing direction and clear opening dimensions, egress paths, and any encroaching architectural, structural, mechanical, or plumbing element
- Equipment elevations showing nameplate heights, gutter and pull-section heights, and the top-of-equipment clearance against headroom and dedicated-space requirements
- Heat-rejection calculations for each room based on equipment nameplate losses, and the corresponding ventilation or mechanical cooling sizing, including airflow paths, intake and discharge locations, and freeze and humidity controls
- Fire-rating coordination drawings showing the rated assemblies enclosing the room, the rating of each, and every penetration through those assemblies with the listed firestop system identified per Firestopping
- Door, frame, and hardware schedule including fire rating, swing direction, panic and access-control hardware, and signage
- Lighting layout with calculation point grid demonstrating compliance with NEC 110.26(D) and the project lighting power density limit
- Power and receptacle plan including dedicated lighting circuit, GFCI convenience receptacles, and any non-room loads that may pass through the dedicated equipment space
- Grounding plan showing the room ground bus, the bonding conductor from the building grounding electrode system, and bonding terminations to each equipment line-up
- Seismic anchorage details for each piece of equipment, with the supporting structural calculations or reference to manufacturer-provided certification
- Security and access control drawings including reader, lock, and contact locations, coordinated with Access Control Systems
☑ Room layout drawings (working space, dedicated space, egress)
☐ Equipment elevations and headroom verification
☐ Heat-rejection and ventilation/cooling calculations
☐ Fire-rating coordination drawings with firestop system schedule
☐ Door, frame, and hardware schedule
☐ Lighting layout and calculations
☐ Power and receptacle plan
☐ Grounding plan and bonding conductor schedule
☐ Seismic anchorage details and calculations
☐ Security and access control drawings
3.1.2 The Contractor shall submit the action submittals listed above for the Engineer's and Architect's review prior to construction of the room and prior to procurement of room-specific products.
3.1.3 Construction of any portion of the room shall not proceed until the corresponding submittals have been reviewed and returned.
3.2 Closeout Submittals
3.2.1 The Contractor shall provide the following at substantial completion:
- As-built room layout, lighting, power, grounding, and ventilation drawings reflecting field conditions
- Field test reports for the room ground bus, working-space verification, illumination measurements, and ventilation airflow per the project commissioning plan
- Operation and maintenance instructions for room-resident systems that are not covered by equipment-specific O&M (door hardware, ventilation, dampers, drainage)
- Warranty documentation for room-specific products
☑ As-built room layout, lighting, power, grounding, ventilation drawings
☐ Field test reports (ground bus, working space, illumination, airflow)
☐ O&M instructions for room-resident systems
☐ Warranty documentation for room-specific products
3.2.2 The Contractor shall provide the closeout submittals listed above at substantial completion.
4 Quality Assurance
4.1 Coordination Authority
NOTE The electrical room is the single most heavily coordinated space in the building. (4.1.1)
4.1.2 The electrical Contractor shall hold a coordination meeting before construction of any electrical room is permitted to proceed beyond rough framing, with the General Contractor, the mechanical and plumbing trades, the structural trade, the fire-protection trade, and the architect of record.
4.1.3 The coordination meeting agenda shall include working-space envelopes, dedicated electrical space, fire-rated boundaries, penetration locations, ventilation routing, drainage path (where any drainage is present at all), and the routing of all conduit, piping, and ductwork that crosses the room.
4.1.4 The coordination meeting minutes shall be incorporated into the project record.
4.2 Regulatory Inspection
4.2.1 Working space, dedicated electrical space, working-space illumination, egress arrangement, and the location of overcurrent devices shall be available for inspection by the Authority Having Jurisdiction before the room is closed up with finishes or before equipment installation reaches a state where the room conditions cannot be measured.
4.2.2 The Contractor shall not conceal any portion of the rated wall, floor, or ceiling assemblies until firestop and assembly inspections have been completed and released.
4.3 Listed and Labeled Components
4.3.1 All firestop systems, fire-rated doors and frames, fire dampers, ventilation equipment, lighting fixtures, and electrical room receptacles and circuits shall be listed and labeled by a Nationally Recognized Testing Laboratory for the application.
4.3.2 Substitution of unlisted products is not permitted in any rated assembly or in any application where the listing is part of the basis of design.
5 Environmental and Service Conditions
5.1 Electrical rooms shall provide a controlled environment so that equipment operates within its nameplate ratings, so that insulation systems and electronics retain their service life, and so that operations and maintenance work is performable safely.
5.2 The Engineer shall establish the project design conditions; the typical default values below shall be adjusted by the project where the connected equipment or the local climate requires it.
5.3 Temperature
6590
7075808590
Default: 75 °F
Per drawings
4070
4050606570
Default: 60 °F
NOTE A 75 °F cooling setpoint is the most common selection for rooms housing typical low-voltage distribution and dry-type transformers and provides margin against equipment derating during summer peak. (5.3.1)
5.3.2 Rooms housing battery systems shall be held closer to 77 °F to maximize battery service life.
5.3.3 Rooms housing equipment rated for 40 °C ambient with no derating may be allowed to drift higher, but the equipment specifier shall confirm that the connected loads, fault levels, and harmonic content do not push the equipment outside its derated capability before allowing a higher setpoint.
5.3.4 A heating setpoint shall be provided wherever the room can drop below the dew point of the surrounding spaces or below the minimum operating temperature of any installed equipment.
NOTE Battery rooms, rooms with electronic protective relays, and rooms with VFDs have higher minimum temperatures than rooms with mechanical-only equipment. (5.3.5)
5.4 Humidity
5095
6070808595
Default: 80 %
5.4.1 Relative humidity in electrical rooms shall be controlled to limit condensation on energized parts, corrosion of bus and connections, and degradation of insulation systems.
5.4.2 Equipment rated for indoor use is generally suitable for non-condensing conditions; condensing conditions are not acceptable in any electrical room governed by this standard.
NOTE Where the room is mechanically conditioned with the rest of the building, the humidity is normally controlled by the central system. (5.4.3)
5.4.4 Where the room is conditioned only by exhaust ventilation, humidity may rise during humid weather and the Engineer shall confirm that the connected equipment is rated for non-condensing operation at the worst-case dew point of the supplied air.
5.5 Particulates and Atmospheric Contaminants
No dedicated filtration — building HVAC serves room
MERV 8 minimum at room supply
MERV 11 (industrial/loading-adjacent)
MERV 13+ (data center adjacent or sensitive environments)
5.5.1 Electrical rooms shall be constructed so that airborne particulates, combustion products, vehicle exhaust, and corrosive vapors do not enter the room from adjacent occupancies.
5.5.2 Where the room is adjacent to a loading dock, a kitchen, a parking garage, a chemical-storage area, or any space with elevated particulate or corrosive loading, the air supply to the electrical room shall be drawn from a cleaner location and filtered as required.
6 Working Space
NOTE The unobstructed working space in front of, and where applicable behind and beside, energized electrical equipment is the single most heavily enforced provision of NEC Article 110. (6.1)
6.2 Working space exists to allow examination, adjustment, servicing, and maintenance of equipment under energized conditions; it shall be kept clear at all times during the life of the building and shall not be used for storage, routing of unrelated trades, or any non-electrical purpose.
6.3 Depth of Working Space — 1000 V and Below
NOTE NEC 110.26(A)(1) establishes three conditions for the depth of working space in front of equipment likely to require examination, adjustment, servicing, or maintenance while energized. (6.3.1)
NOTE The conditions are based on what is on the opposite side of the working space. (6.3.2)
- Condition 1: Exposed live parts on one side of the working space and no live or grounded parts on the other side, or exposed live parts on both sides effectively guarded by insulating material
- Condition 2: Exposed live parts on one side and grounded parts on the other side (concrete, brick, tile walls are considered grounded)
- Condition 3: Exposed live parts on both sides of the working space, not guarded by insulating material, with the operator between
NOTE Working space depth is then determined by the nominal voltage to ground and the governing condition. (6.3.3)
NOTE For installations 151 V to 600 V to ground (the dominant case for 277/480 V systems with neutral grounded), Condition 1 requires 3 ft, Condition 2 requires 3 ft 6 in., and Condition 3 requires 4 ft. (6.3.4)
NOTE For installations 0 V to 150 V to ground, all conditions require 3 ft. (6.3.5)
NOTE For installations 601 V to 2500 V, Condition 1 requires 3 ft, Condition 2 requires 4 ft, and Condition 3 requires 5 ft. (6.3.6)
6.3.7 The full table is at NEC 110.26(A)(1) and shall be consulted for any voltage class not listed above.
● Condition 1 — exposed parts on one side only
○ Condition 2 — exposed parts opposite grounded surface
○ Condition 3 — exposed parts on both sides
Per drawings
6.3.8 The full working space depth table at NEC 110.26(A)(1) shall be consulted for any voltage class not listed above.
6.3.10 Where two facing equipment line-ups create a Condition 3 situation, both shall be served by a single working space measured between the equipment faces, sized for Condition 3 at the higher voltage class present.
6.3.11 The working space shall not be shared with the working space of equipment on a perpendicular wall except where physically possible without obstruction.
6.4 Width and Height of Working Space
6.510
6.578910
Default: 6.5 ft-in
6.4.1 Per NEC 110.26(A)(2), the width of working space in front of electrical equipment shall be the width of the equipment or 30 in., whichever is greater.
6.4.2 The working space shall permit at least a 90-degree opening of equipment doors or hinged panels, in accordance with NEC 110.26(A)(2).
6.4.3 Per NEC 110.26(A)(3), the height of working space shall be 6 ft 6 in., or the height of the equipment, whichever is greater.
6.4.4 The 6 ft 6 in. minimum is measured from the floor or platform; equipment, raceway, piping, lighting fixtures, and HVAC components shall not encroach on this volume.
6.4.5 Where equipment is more than 6 ft 6 in. tall, the working space shall extend to the top of the equipment.
6.4.6 Switchgear, motor control centers, and switchboards routinely exceed 6 ft 6 in., and the working space height shall be increased correspondingly.
6.5 Working Space — Over 1000 V
NOTE For equipment rated over 1000 V, NEC 110.34 establishes a separate working space table with greater clearances and additional rules. (6.5.1)
NOTE For 1001 V to 2500 V, Condition 1 requires 3 ft, Condition 2 requires 4 ft, and Condition 3 requires 5 ft. (6.5.2)
NOTE For 2501 V to 9000 V, Condition 1 requires 4 ft, Condition 2 requires 5 ft, and Condition 3 requires 6 ft. (6.5.3)
6.5.4 The full working space table at NEC 110.34(A) shall govern any installation over 1000 V.
6.5.5 Working space over 1000 V shall be guarded per NEC 110.31.
6.5.6 Access to working space over 1000 V shall be permitted only to qualified persons, and the room shall be equipped with the entrance and egress provisions of NEC 110.33.
7 Headroom and Equipment Height
NOTE This is a clear-volume requirement, not a finished-ceiling dimension. (7.1)
916
91011121416
Default: 12 ft-in
Per drawings
7.2 Per NEC 110.26(A)(3), the minimum headroom of working spaces about service equipment, switchboards, panelboards, and motor control centers shall be 6 ft 6 in.
7.3 Where the electrical equipment exceeds 6 ft 6 in. in height, the minimum headroom shall not be less than the height of the equipment.
7.4 Lighting fixtures, sprinkler piping, HVAC ductwork, and structural members all count against headroom when they intrude into the volume above equipment.
NOTE A 12 ft clear room height is a practical default for rooms with low-voltage switchgear (typically 90 in. to 96 in. tall) because it accommodates the 6 ft of dedicated equipment space above the switchgear with margin for conduit, lighting, and HVAC. (7.5)
7.6 Rooms with medium-voltage switchgear or with very tall lineups require greater clear height.
7.7 Coordinate with the equipment manufacturer's shop drawings before finalizing the room dimensions.
8 Dedicated Equipment Space
NOTE The dedicated electrical space is one of the most commonly violated provisions in field conditions; the space above each line-up is reserved for electrical use only. (8.1)
● None — open to structure
○ Dropped ceiling above dedicated space envelope (foreign systems above only)
8.2 Per NEC 110.26(E), the space equal to the width and depth of the equipment and extending from the floor to a height of 6 ft above the equipment, or to the structural ceiling if lower, shall be reserved for electrical installations exclusively.
8.3 No piping, ductwork, or other equipment foreign to the electrical installation shall be installed in or pass through the dedicated electrical space.
8.4 Sprinklers, fire-suppression piping, and similar systems serving the room itself are permitted in the dedicated space provided they do not interfere with equipment access.
NOTE The 6 ft above each piece of switchgear, switchboard, panelboard, and motor control center is not free volume that mechanical or plumbing trades may use for their distribution mains. (8.5)
8.6 Where the structural ceiling is lower than 6 ft above the equipment, the entire vertical run from the equipment to the structural ceiling is dedicated and protected.
8.7 Where the room ceiling exceeds 6 ft above the equipment and a finished or dropped ceiling is present, the volume above the dropped ceiling outside the dedicated space envelope may be used for non-electrical systems, provided a suitable barrier (such as the ceiling itself) is installed to prevent any leak or condensation from foreign systems from impinging on electrical equipment.
NOTE NEC 110.26(F) further restricts piping and ductwork that may pass through electrical rooms; see Drainage and Plumbing Restrictions, below. (8.8)
9 Door and Egress
● Out of room in direction of egress
○ Into room (only where equipment rating <800 A and no panic-hardware trigger)
Per drawings
● Listed panic hardware (free egress from inside without tools)
○ Listed fire-exit hardware (on rated door)
○ Standard latch (only where panic hardware not required)
9.1 Doors to electrical rooms shall open in the direction of egress per NEC 110.26(C)(3) for equipment rated 800 A or more.
9.2 Door swing shall be coordinated with the egress path of any room occupant under fault conditions.
9.3 Doors shall be equipped with panic hardware or other listed fire-exit hardware that opens under simple pressure from inside the room without keys, tools, or special knowledge, per NEC 110.26(C)(3).
9.4 The room shall be capable of being secured against unauthorized entry from outside while preserving free egress from inside; locking devices that prevent egress are prohibited.
9.5 Where the room is publicly accessed for any reason, ICC A117.1 accessibility requirements apply to the path of travel, the door operating effort, and the threshold.
NOTE The working space inside the room is exempt from accessibility maneuvering clearance requirements because operating personnel are qualified persons under NEC and not public users. (9.6)
9.7 Number of Entrances and Doors
● Single entrance (equipment <1200 A or alternate provision met)
○ Two entrances, one at each end of the working space
Per drawings
3248
32364248
Default: 36 in
9.7.1 Per NEC 110.26(C)(2), for equipment rated 1200 A or more and over 6 ft wide that contains overcurrent devices, switching devices, or control devices, the room shall have one entrance not less than 24 in. wide and 6 ft 6 in. high at each end of the working space.
9.7.2 A single entrance is permitted where the location permits a continuous and unobstructed way of egress travel, or where the working space depth is twice that required by NEC 110.26(A)(1) so that personnel can move away from the equipment in either direction.
9.7.3 Equipment shipping splits, replacement section sizes, and racking devices for drawout breakers shall be verified against the door opening before construction so that future replacement is not constrained by the room itself.
9.7.4 Where any section of the largest installed equipment cannot pass through the smallest door of the room, the door schedule shall be revised.
10 Fire Resistance Ratings
NOTE The enclosing assemblies of an electrical room — walls, floor, and ceiling — are rated based on the occupancy classification of the building and the role of the room, and are governed by the International Building Code. (10.1)
NOTE Electrical rooms are commonly classified as utility (Section 304) or as accessory to the principal occupancy. (10.2)
Not rated (small private rooms, low occupancy load adjacent)
1 hour
2 hour
3 hour
Per drawings
● ASTM E119 / UL 263 listed wall and floor/ceiling assembly
○ Per IBC prescriptive table
10.3 The Electrical Engineer shall coordinate with the Architect of Record to confirm the required fire-resistance ratings.
NOTE Where the room serves multiple tenants or stories, separation requirements increase. (10.4)
NOTE Where the room contains equipment rated for the entire building service, additional separation is often required by the building code or by insurer requirements. (10.5)
NOTE A 2-hour rating is a defensible default for rooms containing service entrance equipment, equipment serving multiple tenants, or equipment with main devices rated 1200 A or more in multi-story buildings; a 1-hour rating is common for distribution closets serving a single tenant or floor. (10.6)
10.7 The Architect of Record shall confirm the required rating by reference to the building code occupancy and construction type.
10.9 The wall, floor, and ceiling assemblies shall be constructed under Gypsum Board Assemblies or the applicable structural and architectural scopes. 10.10 Penetrations of the rated assemblies for raceway, cable tray, ductwork, sprinkler piping, and any other service shall be sealed with listed firestop systems per Firestopping. 11 Ventilation and Cooling
NOTE Electrical equipment converts a small fraction of its throughput to heat under normal operation, and a larger fraction during fault conditions or after motor starts. (11.1)
○ Exhaust ventilation (gravity or fan-driven) with outside air supply
● Mechanical cooling (dedicated CRAC or split system)
○ Connection to building HVAC system
○ Hybrid — ventilation primary, mechanical cooling supplemental
Equipment manufacturer published nameplate losses
Calculated from connected load and equipment efficiency
Per ASHRAE Applications guidance for electrical rooms
● Outdoor air directly (louver to exterior)
○ Outdoor air via ductwork from a clean intake
○ Building return / recirculated air
● Direct to exterior louver
○ Ducted to exterior, with fire damper at rated wall penetration
○ Into building return (only with documented heat capture in the building system)
11.2 The room shall reject equipment heat continuously so that the equipment ambient does not exceed its nameplate rating.
11.3 Heat-rejection calculations shall be performed for every electrical room and shall be based on the equipment nameplate losses, the connected load profile, and the worst-case simultaneity factor for the installed equipment.
NOTE Mechanical cooling is the default for rooms housing service entrance equipment, switchgear, motor control centers, and transformers in temperate and warm climates because it provides reliable temperature and humidity control independent of outdoor conditions. (11.4)
NOTE Exhaust ventilation is appropriate for small distribution closets in mild climates and for rooms whose connected load profile keeps heat rejection low. (11.5)
NOTE Connection to the building HVAC system is appropriate only where the room's continuous cooling demand is small relative to the building system and where the building system runs continuously, because the building system is typically scheduled off during unoccupied hours when electrical loads continue. (11.6)
11.7 Ventilation intake and discharge openings shall be located so that the air path crosses the equipment line-up and so that hot discharge air is not re-entrained.
11.8 Where the room is on the building exterior, intake and discharge louvers shall be weatherproof, bird-screened, and protected against snow loading and wind-driven rain.
11.9 Where intake or discharge passes through a rated wall, listed fire dampers shall be provided per Firestopping and the mechanical scope. 11.10 Where the room contains a battery system, hydrogen evolution shall be addressed per Dc Battery Systems and IEEE 484 or IEEE 1187, with ventilation rates sized to limit hydrogen accumulation below 1 percent of room volume. 12 Illumination
12.1 Illumination of working spaces about indoor electrical equipment is required by NEC 110.26(D) and shall be manually controllable, of adequate level, and backed by emergency lighting.
● Manual switch at door (occupancy sensor permitted as supplement only)
○ Three-way switching at each entrance
○ Manual override with vacancy sensor (occupant must turn on)
30100
305075100
Default: 50 fc
Per drawings
● Battery-backed luminaire (90-minute minimum per NFPA 101)
○ Connection to building emergency branch
○ Both — separate sources for redundancy
12.2 Per NEC 110.26(D), illumination shall be provided for all working spaces about service equipment, switchboards, panelboards, and motor control centers installed indoors.
12.3 The illumination shall not be controlled by automatic means only — manual control shall be provided so that personnel entering the room can confirm the lights are on.
NOTE The intent is that a worker entering the room cannot be left in the dark by an occupancy-sensor timeout or by a building-management schedule. (12.4)
NOTE A maintained 50 footcandle level on a vertical reference at the equipment face is the typical default and supports nameplate reading, breaker handle identification, and visual inspection. (12.5)
12.6 Higher levels (75 to 100 footcandles) shall be provided where infrared scanning windows are routinely used or where the equipment line-up is densely labeled.
12.7 Lower illumination levels are not acceptable in rooms with switchgear or motor control centers.
12.8 The lighting power density of the room shall comply with ASHRAE 90.1 or the adopted IECC, whichever is more stringent.
12.9 Emergency lighting shall be provided per NFPA 101 to maintain the means of egress under loss of normal power.
12.10 Where the room itself houses the building's emergency or standby source, the emergency lighting shall be supplied from a separate source from the equipment under maintenance (typically a battery-backed luminaire).
12.11 Lighting fixtures shall not be installed within the dedicated equipment space envelope.
13 Power and Receptacles
13.1 Convenience receptacles and the room lighting circuit shall be powered from a source independent of the equipment under maintenance, so that de-energizing that equipment does not disable the tools and lights needed to service it.
One GFCI 125V receptacle within 25 ft of each equipment line-up (NEC 210.63 minimum)
GFCI receptacles at each end of the working space
Receptacles along each wall at 12 ft maximum spacing
● Dedicated lighting circuit, fed from outside the room
○ Dedicated lighting circuit, fed from room panel (only where alternate access to lighting exists)
13.2 Per NEC 210.63, a 125 V, single-phase, 15 A or 20 A receptacle outlet shall be installed in an accessible location within 25 ft of each piece of service equipment, switchboard, panelboard, or motor control center.
13.3 The receptacle shall not be connected to the load side of the equipment it serves, so that if the equipment is de-energized for maintenance the receptacle remains energized for test instruments, work lights, and tools.
13.4 The receptacle shall be fed from a panel in an adjacent area or from a dedicated panel that is not part of the maintained equipment.
13.5 Receptacles in electrical rooms shall be GFCI-protected per NEC 210.8 where required by the room's classification (unfinished spaces, similar conditions).
13.6 Receptacles shall not be installed inside the dedicated equipment space envelope of NEC 110.26(E).
13.7 The lighting and receptacle circuits shall not be fed from the equipment under maintenance in the room.
NOTE Powering the room's own lights and receptacles from the main panel housed in the room is a common error, because taking the main panel out of service then plunges the room into darkness and disables the receptacles needed for tools. (13.8)
14 Drainage and Plumbing Restrictions
14.1 Foreign piping is excluded from the dedicated equipment space, and any drainage provided shall be located clear of equipment and the working space.
○ Not permitted (no piping through room)
○ Permitted outside dedicated space, with drip pans and leak detection above equipment
● Permitted outside dedicated space, no piping over equipment
● No floor drain (room with no plumbing exposure)
○ Floor drain provided at low point, located clear of equipment
○ Floor drain with trap primer, located clear of equipment
14.2 Per NEC 110.26(F), piping and ductwork foreign to the electrical installation shall not be located in the dedicated equipment space envelope.
14.3 Beyond the dedicated space envelope, plumbing and HVAC systems may pass through the electrical room but shall be arranged so that any leak, condensation, or rupture cannot impinge on electrical equipment.
14.4 Where any piping passes through the room, it shall be located so that no portion of the piping is above any equipment.
14.5 Where piping above equipment is unavoidable, listed drip pans with leak alarms shall be installed below the piping and above the equipment, and the leak alarm shall be wired into the building management system.
14.6 Sprinkler piping serving the electrical room itself is permitted in the dedicated space provided it does not interfere with equipment access.
14.7 The discharge of water onto energized equipment shall be addressed by the fire-protection scope through pre-action systems or equivalent measures where the project warrants.
14.8 A floor drain shall be provided in any electrical room with plumbing exposure, with sprinkler protection, or with a battery system, located at the low point of a sloped floor and clear of any equipment line-up.
14.9 The floor drain shall be sized and routed so that it does not introduce sewer gas or vermin into the electrical room.
14.10 Drains shall not be located within the working space or the dedicated equipment space.
15 Grounding and Bonding
NOTE A dedicated equipment ground bus provides a single termination point for the equipment grounding conductors of each line-up, for the grounding conductors of raceway systems entering and leaving the room, and for the bonding of metallic structural elements within the room. (15.1)
● Tin-plated copper bar, full length of equipment line-up
○ Bare copper bar, full length of equipment line-up
○ Multiple distributed ground bars bonded together
● Per [[sync/grounding-and-bonding]] and NEC Table 250.66
○ As shown on the grounding riser
15.2 A dedicated equipment ground bus shall be provided in each electrical room and shall be bonded to the building grounding electrode system per Grounding And Bonding. 15.4 Where the room contains telecommunications grounding equipment as a separate scope, the telecommunications ground bar shall be bonded to the building grounding electrode system per Telecommunications Bonding and shall not be mixed with the electrical room equipment ground bus. 16 Equipment Anchorage and Seismic
16.1 Equipment shall be anchored to resist the design lateral loads, and seismically certified where the seismic design category requires it.
A or B (no special anchorage)
C
D
E or F
Not required by seismic design category
IBC/ASCE 7 — Importance Factor 1.0
IBC/ASCE 7 — Importance Factor 1.5 (essential facility)
OSHPD pre-approval (California healthcare)
16.2 Equipment in electrical rooms shall be anchored to resist the design lateral loads per ASCE 7 and the applicable building code.
16.3 Anchorage shall be coordinated with the structural design of the floor or housekeeping pad.
16.4 Where the building site is in a seismic design category that requires seismic certification of nonstructural components, the equipment shall be seismically certified per ICC ES AC156 by shake-table testing or by analysis per ASCE 7.
16.5 Concrete housekeeping pads shall be provided beneath floor-mounted equipment, dimensioned to extend at least 3 in. beyond the equipment base on all sides and reinforced to receive the anchorage in accordance with the equipment manufacturer's published mounting details.
17 Security and Access Control
17.1 Electrical rooms shall be secured against unauthorized entry while preserving free egress from inside.
Mechanical key only
Electronic card or credential reader
Electronic reader with audit trail and remote enable/disable
Reader plus video surveillance
○ None
● Door contact reported to BMS or security panel
○ Door contact plus interior motion sensor
17.2 Electrical rooms shall be secured against unauthorized entry.
17.3 Access shall be limited to qualified persons under NEC and to maintenance and operations personnel authorized by the building owner.
17.4 Where the building employs an electronic access control system, the electrical room doors shall be on the system per Access Control Systems. 17.5 Where a mechanical key system is used, the keying shall be coordinated with the door hardware schedule and with the owner's key control policy.
17.6 Free egress from the inside of the room shall not be impeded by any security device; locking devices that defeat panic hardware are prohibited per NFPA 101.
17.7 Mantraps and similar restrictive entry devices shall not be installed on electrical rooms unless specifically required by the owner and approved by the AHJ.
18 Finishes
18.1 Floor
Sealed concrete
Sealed concrete with anti-static topping
Epoxy coating
Resilient flooring (small distribution closets only)
18.1.1 Electrical room floors shall be sealed concrete or another smooth, non-absorbent, easily cleaned finish that does not generate dust and that does not retain moisture.
18.1.2 The floor shall be level under each equipment line-up to the tolerance required by the equipment manufacturer, typically 1/8 in. in 10 ft.
18.1.3 Where mineral-oil-filled or fluid-cooled equipment is installed, the floor shall be sloped to the floor drain and provided with a containment curb sized to retain the equipment's fluid volume.
18.1.4 Anti-static or static-dissipative floor finishes shall be provided in rooms with electronic protective relays, in battery rooms where qualified, and in rooms specifically designated for sensitive equipment.
18.1.5 Carpeted floor finishes shall not be installed in electrical rooms.
18.2 Walls and Ceiling
Painted gypsum board on rated assembly
Painted concrete masonry unit
Painted concrete (exposed structure)
18.2.1 Wall and ceiling finishes shall be non-combustible, low-dust, and compatible with the required fire-resistance rating.
NOTE Painted gypsum board, painted concrete masonry unit, and painted concrete are common wall and ceiling finishes. (18.2.2)
18.2.3 Acoustical ceiling tile is permitted outside the dedicated equipment space envelope, provided it is rated for the assembly and does not interfere with the rated boundary.
19 Signage
☐ 'High Voltage — Authorized Personnel Only' (where applicable)
☑ 'Danger — Electrical Hazard' at door
☐ Arc-flash boundary warning at entrance
☐ Available fault current and date (NEC 110.24)
☐ No-smoking sign (battery rooms)
19.1 The room and its equipment shall be signed per NEC 110.16 (arc-flash hazard warning), per NEC 110.21 (equipment identification), and per the project equipment-labeling standard Equipment Labeling. 19.2 Signage shall be durably affixed and legible from a distance equal to the working space depth.
19.3 Signs that are required by code shall not be obstructed by equipment, finishes, or accessory installations.
20 Cable Pathways
20.1 Conduit, cable tray, and busway entry shall be coordinated with the working space, the dedicated equipment space, and the rated-wall penetration locations.
● Bottom entry (through floor or housekeeping pad)
○ Top entry (through ceiling)
○ Side entry (through wall)
○ Combination per equipment
Per drawings
20.2 Conduit, cable tray, and busway entering and leaving the electrical room shall comply with Raceways And Conduit. 20.3 The room layout shall identify top-entry, bottom-entry, and side-entry zones for each equipment line-up and shall coordinate entry zones with the working-space envelope, the dedicated equipment space, and the rated-wall penetration locations. 20.4 Penetrations of rated wall, floor, and ceiling assemblies for cable pathways shall be sealed with listed firestop systems per Firestopping. 20.5 Sleeves provided through cast-in-place concrete floors shall extend a minimum of 2 in. above finished floor where cable enters from above the floor so that water and debris on the floor do not enter the raceway system below.
21 Coordination with Other Trades
21.1 The electrical Contractor shall coordinate the following at minimum with the listed trades during shop drawing review and prior to room construction.
- Architectural: room dimensions, finishes, doors and hardware, signage, accessibility path
- Structural: housekeeping pads, equipment loads, seismic anchorage, slab depressions, equipment-pad reinforcement
- Mechanical: ventilation airflow, intake and discharge louver locations, fire dampers at rated penetrations, room thermal load, condensate management
- Plumbing: avoidance of foreign piping in the dedicated equipment space, floor drain location and trap priming, any required eyewash for battery rooms
- Fire protection: sprinkler coverage and discharge characteristics in rooms with energized equipment, pre-action vs. wet-pipe selection, drain location for sprinkler test
- Telecommunications: separation from telecom rooms, grounding interface with telecommunications bonding backbone per Telecommunications Bonding
- Security: access control reader, lock, and door contact installation per Access Control Systems; video coverage where required
21.2 The electrical Contractor shall coordinate the listed scopes with the listed trades during shop drawing review and prior to room construction.
21.3 Conflicts identified during coordination shall be resolved before the affected scope proceeds.
21.4 Where a coordination conflict has no other resolution, the electrical room requirements of this standard and NEC Article 110 shall govern, because the room is a code-required envelope and other trades' routing is generally adjustable.
22 Commissioning
22.1 Each electrical room shall be commissioned as part of the integrated systems testing of the building.
22.2 Commissioning of the room itself, distinct from the equipment within it, shall verify the following at minimum.
- Working space dimensions verified by direct measurement against the approved layout
- Dedicated equipment space envelope clear of foreign systems
- Door swing, panic hardware, and egress lighting functional
- Lighting illuminance measured at the working plane and compared to the design value
- Ventilation airflow measured at intake and discharge, including any fire damper actuation tests
- Room temperature held to setpoint with the connected load at the project commissioning load case
- Ground bus bonded and resistance to the building grounding electrode system verified
- Convenience receptacles functional, GFCI test-trip-reset confirmed
- Access control functional, audit trail recording confirmed where applicable
- Signage installed, complete, and legible
☑ Working-space dimension verification
☐ Dedicated equipment space verification
☐ Door swing, panic hardware, egress lighting
☐ Illumination measurement at working plane
☐ Ventilation airflow and fire-damper testing
☐ Temperature verification under load
☐ Ground bus and bonding verification
☐ Receptacle and GFCI testing
☐ Access control functional and audit verification
☐ Signage verification
22.3 Each electrical room shall be commissioned as part of the integrated systems testing of the building.
22.4 Commissioning of the room itself, distinct from the equipment within it, shall verify the items listed above at minimum.
22.5 Commissioning reports shall be incorporated into the closeout submittals.
23 Delivery, Storage, and Handling (During Construction)
23.1 The electrical room shall not be used for storage of construction materials, tools, or trades' equipment beyond what is required to complete the work of the room itself.
23.2 Equipment delivered to the room before the room is enclosed and conditioned shall be protected from weather, dust, and moisture per the equipment manufacturer's storage requirements.
23.3 Where the room becomes enclosed but is not yet conditioned, condensation heaters in the equipment shall be energized from a temporary source.
23.4 During construction, the working space and dedicated equipment space of installed equipment shall be respected by all trades, even where finished construction is not yet complete.
23.5 Installation of foreign piping, ductwork, or finishes that would later require removal to comply with NEC 110.26 shall not proceed.
24 Warranty
1 year from substantial completion
2 years from substantial completion
24.1 The Contractor shall warrant the room installation including doors, hardware, finishes, lighting, ventilation, drainage, ground bus and bonding, and signage, for the project warranty period.
24.2 Products carrying a manufacturer warranty shall be warranted to the Owner for the manufacturer's published warranty period.