Your questions answered: Electrical systems: Designing electrical rooms

Unanswered questions from the Nov. 16, 2017, webcast on designing electrical rooms are addressed by the presenters.


Switchboards, switchgear, transformers, generators, and UPSs require space for installation, maintenance, heat dissipation, and possible future expansion. And the wiring, busways, and raceways that distribute the electrical power must be accounted for—now, and in the future. Documentation and monitoring of electrical system’s equipment and how it connects to the rest of the facility must be accurately maintained.

Questions not addressed during the Thursday, Nov. 16, 2017, webcast on Electrical systems: Designing electrical rooms are addressed by the presenters here.


  • Mario Vecchiarello, PE, CEM, GBE, Senior Vice President, CDM Smith, Boston
  • Rich Vedvik, PE, Senior Electrical Engineer and Acoustics Engineer, IMEG Corp., Rock Island, Ill.

Question: Which exact code section defines battery light requirement inside electrical room? Does this rule apply to the main electrical room only?

Rich Vedvik: Not all electrical rooms are required to have battery emergency lightings. NFPA 110 7.3 defines the requirement for Level 1 and Level 2 emergency power supply (EPS) locations (this is echoed in NFPA 70: National Electrical Code (NEC) 517.33 (E). It is recommended to provide battery-powered emergency lighting in main electrical rooms, rooms containing emergency power supply system (EPSS) equipment, and electrical rooms without emergency power.

Question: What are the minimum dimensions needed for electric room for proper ventilation?

Mario Vecchiarello: Room size (and layout) are not prescriptive and depend on the equipment installed within the room, the arrangement available, and the type(s) of ventilation provided. Room and ventilation design, however, should take into consideration equipment that produces more heat gain than others.

Question: In a residential high rise: What is the maximum distance tap for the fire pump switch location? Is it required to be located in a dedicated space in the electrical room?

Vedvik: NEC 695 references NEC 230.82 for service tap requirements. NEC 695 contains fire pump requirements and note the 2-hour rating requirement. It is expensive to route 2- hour fire rated conductors in a building that promotes some coordination with locations of power source and equipment. Also note the requirement in 695.3(A)(1) for the fire pump tap to be in a separate vertical section and also physically separated from the electrical source; this requirement increases the size of the gear and thus the electrical room. The 2015 edition of the International Building Code (IBC) 403.3.4 identifies fire pump room requirements.

Question: What is the lighting requirement in electrical rooms?

Vecchiarello: See NEC Section 110.26(D) for normal lighting and other areas of the NEC and NFPA 101: Life Safety Code for emergency egress lighting requirements.

Question: With regard to a platform for a platform having a 6.9 kV switchgear, it is mounted on an ISO footprint where the distance would not meet NEC requirements as per distance/workspace. Can I add a flip-down structure to get to the 5 or 6 ft needed?

Vedvik: One concern with this method is providing fall protection on the flip-out platform. I have seen these platforms used before, but they usually lack fall protection. The NEC 110.26 clearances are relative to physical surfaces and not specifically working space for equipment. If a flip-down structure is added, the fall protection would need to comply with working clearances in NEC 110.26. NEC 408.18 references 110.26 for clearances around switchgear.

Question: What are the required room conditions for an oil-filled transformer to be in the room (such as an indoor substation)?

Vedvik: Refer to NEC 450.26 for vault construction requirements.

Question: How do you estimate heat gain of equipment?

Vecchiarello: Calculate the total heat dissipation for all the pieces of equipment, such as breakers, starters, VFDs, transformers, batteries, and battery chargers, etc. (should review the information data sheet on all of this equipment).

For double-ended equipment, we would typically account for only one transformer in a unit substation operating at rated load and the other operating at no load. Therefore, we would include the total losses for one transformer, which includes the active full load losses and the no load losses, and the no load losses for the other transformer.

Question: You said NFPA does not permit automatic transfer switch (ATS) and panels in the uninterruptible power supply (UPS) room. Did you mean in the generator room?

Vedvik: NFPA 110.7.2 does permit EPSS equipment to be located within the EPS room. Thanks for helping to clarify this.

Question: NFPA 70E would seem to affect clearances more than other codes. Comments?

Vedvik: The 2015 edition of NFPA 70E only contains five instances of the word “clearance.” NFPA 70E defines requirements for the execution of work while NFPA 70 defines requirements for equipment and spaces containing equipment. NFPA 70E Tables 130.4(D)(a) and (b) identify approach boundaries to live conductors for personnel. These requirements do not change the distances in NFPA 70 110.26 and 110.34 for clearances around electrical equipment. NFPA 70E Annex C.2.1 references NEC 110.26 and 110.34 for working spaces.

Question: What have you seen go wrong in electrical rooms?

Vecchiarello: Several things, including:

·        Equipment purchased is larger than anticipated.

·        Systems foreign to the electrical installation encroaches on the dedicated equipment space and working space.

·        Water leaking on electrical equipment.

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