NEC Article 110.34: Electrical Room "Basics" - Electrical Equipment Rated at 1,000 V or More, Article #3 of 3


Dear Colleague:

To re-cap Article #1 from March 5th and as required by OSHA, NFPA and the NEC:  "working space around electrical enclosures or equipment shall be adequate for conducting all anticipated maintenance and operations safely, including sufficient space to ensure the safety of personnel working during emergency conditions and workers rescuing injured personnel."

These requirements vary depending on whether the electrical equipment is rated at (1) 1,000 volts or less (SeeArticle #2) or (2) over 1,000 volts. This article reviews (2) when the electrical equipment is 1000 V or more.

Electrical Room (2)Minimum clearances in front of electrical equipment (600 V (now 10000 V) or more);

NEC Table 110-34, updated from 600 V to 1000 V in 2017

Minimum clearances are established for work spaces in front of high voltage - electrical equipment such as switchboards, control panels, switches, circuit breakers, switchgear and motor controllers.  These distances indicate space that must be clear to the floor.

The chart above illustrates the varying requirements for the depth of the working space in the electrical room based on existing conditions. As outlined in NEC Table 110.34(A),these are:

  - Condition 1: When there are (i) exposed live parts on only one side of the working space, (ii) grounded live parts on the other side of the working space, or  (iii) when both sides of the working space are sufficiently insulated. Requires 3 - 8 ft. depending on voltage from 1001V to above 75 kV.

 - Condition 2: When exposed live parts are on one side of the working space and grounded parts on the other side. Concrete, brick or tile walls are considered "grounded".Requires 4 -10 ft. depending on voltage from 1001V to above 75 kV.

 - Condition 3: Both sides of the working space have exposed live parts. Requires 5 - 12 ft. depending on voltage from 1001 V to above 75 kV.

The minimum depth of clear working space for electrical equipment for each of the 3 conditions is stated in NEC Table 110.34.

Additional requirements for electrical rooms include:

  • equipment operating over 1000 V must be separated from lower voltage equipment by a fence or other suitable partition, except for lower voltage switches for the electrical equipment located in the room NEC 100.34 (B)
  • for equipment over 1000 V with live parts or exposed conductors, the entrance must be either locked or guarded at all times NEC 100.34 (C)
  • for equipment over 1000 V with live parts or exposed conductors, there must be permanent and conspicuous danger signs posted  NEC 100.34(C)
  • working spaces must have lighting with outlets arranged so that workers changing lamps/making repairs are not endangered by live parts or equipment NEC 100.34(D)
  • unguarded live parts must be elevated as required by NEC Table 110.34(E)
  • unrelated pipes and ducts cannot be located in the electrical room NEC 100.34(F)
  • the electrical room must be protected from leaks and condensation from systems unrelated to the electrical equipment NEC 100.34(F)

Other requirements apply to communications systems which are covered by other NEC standards as well as the standards of the IT industry.

Again, our thanks to Somesh Gailkwa at New Jersey Engineers for sharing this topic with us.

Correction:  before 2017, the threshold divider was 600 Volts, but is now 1000 Volts. The required distances for  threshold values have not changed.

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About The Author

James Khalil, P.E. is President, Co-founder and Inventor of PowerCalc. He has 30+ years of experience at his MEP firm in Delray Beach, FL and with Carter Burgess (now Jacobs) in Fort Worth, TX; Mason & Hanger (now Zimmerman) in Lexington, KY; and Gee & Jenson (now CH2M) in West Palm Beach, FL. He received his B.S. in Electrical Engineering from the University of Texas. His experience includes projects for Saudi Arabia and Qatar; the US Departments of Energy, State, and Defense; and universities, schools, health facilities, and arts centers.