NEC Article 110: Electrical Room "Basics" - Electrical Equipment Rated at 600 V or Less, Article #2 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 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)

600 volts or less or (2) over 600 volts. This article reviews (1) when the electrical

equipment is 600 V or less.



Minimum clearances in front of electrical equipment (600 V or less); 

NEC Table 110-16(a); OSHA Table S-1

These requirements apply to the width, depth, and height of these working spaces. To avoid body contact with energized parts when maintaining / servicing electrical equipment, a minimum of 30 inches is required in front of electrical equipment rated 600 V or less. This space depth must be clear to the floor. If rear access is also required to work on de-energized parts, then another minimum of 30 inches is required to ensure adequate access.

All 30 inch "buffer zones"  must also allow for equipment doors and hinged panels to open at a 90 degree angle to allow for the servicing of the equipment.

The chart above illustrates the varying requirements for the depth of the working space in the electrical room based on existing conditions. These are:

  - Condition 1: When there are exposed live parts on only one side of the working space, or,  when both sides of the working space are sufficiently insulated.

 - Condition 2: When there are exposed live parts on one side of the working space and grounded parts on the other side. Concrete, brick or tile walls are considered "grounded".

 - Condition 3: Both sides of the working space have exposed live parts.

To summarize NEC Table 110.25(A)(1), the minimum working space in an electrical load for 0-600 V installations:

         .       3 feet between insulated materials

         .       3.5 feet between grounded equipment

         .       4 feet between exposed live parts

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

Our next article will complete this 3 part series and address the requirements of electrical rooms for equipment rated over 600V.

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

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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.