As a guest speaker at a meeting of electricians, I was asked to address how to determine the number of receptacles required for commercial buildings and if their installation requirements and spacing procedures were regulated in the same manner as for dwelling units. I was amazed at the -misinterpretations that concerned this subject. I realized that electricians wiring receptacles in commercial buildings have a totally different point of view than those wiring dwelling units.
Electricians ask, when they have the responsibility of determining the number of receptacle outlets required within a commercial building, what is an easy way to determine the volt-amperes (VA) and number needed? The National Electrical Code (NEC), I explained, normally requires each receptacle outlet to be calculated at 180 VA [120V 20A overcurrent protection device (OCPD) ÷ 180 VA = 13 outlets]. And when the total VA exceeds 10,000, the first 10,000 VA may be calculated at 100 percent and the remaining VA at 50 percent per Table 220.44. For banks, offices or dwelling units, see Table 220.12 (with references), and either use 1 VA per square foot or the number of receptacle outlets installed, whichever is applicable.
Number and spacing
I informed them that receptacle outlets installed in dwelling units are spaced and located differently than those in commercial facilities. Therefore, receptacle outlets (number) can be installed in the needed areas, or as the owner requires, or as, in some instances, where dictated by the NEC.
I pointed out that Table 220.12 should be used to calculate the number of receptacle outlets to be installed in dwelling units. For example, select 3 VA per square foot from the table. Then divide 120V times 20A OCPD by this number (3 VA) to derive 800 square feet. And based on this concept, there is no limit to the number of outlets permitted. The square footage for a 15A circuit and the outlets permitted are determined using the same procedure. The authority having jurisdiction may not agree with this procedure, so they may put a limit on the number of receptacle outlets permitted on a circuit.
By fielding questions, I learned that many electricians who wire receptacle outlets in commercial buildings do not perform wiring in dwelling units and are a little lost when working on residential properties.
Height of receptacles
One question was about the height that a receptacle could be installed in a dwelling unit and whether it could count as a required outlet? Receptacles located more than 5 feet above the floor may not be considered as required outlets as restricted by 210.52(4). I suggested that electricians installing receptacle outlets should review and recognize the requirements in 210.52(1) through (3).
The 6-foot rule for spacing receptacle outlets in the rooms per 210.52(A) basically requires that no point measured horizontally along the floor line in any wall space is more than 6 feet from a receptacle outlet. A wall space is considered any space that is 2 feet or more in width, including around corners or unbroken along the floor line. Items breaking the floor line can be found in 210.52(A). As stated in 210.52(A)(3), floor receptacles counting as a required outlet must be located within 18 inches of the wall.
To comply with the 6-foot rule, I pointed out that the general rule requires a receptacle outlet to be installed along an unbroken floor line at least every 12 feet.
Small appliance circuits
One electrician, who seemed to have experience wiring dwelling units, commented that at least two small appliance circuits had to be installed in the kitchen, pantry, breakfast room, dining room or similar area. He asked when are more than two required and how to make this determination. Based on my experience, one of two methods is used to determine when more than two is necessary. The square footage is first. Multiply 120V by 20A OCPD and divide by 3 VA, and it equals 800 square feet. Two 20A circuits using this method provides 1,600 square feet (800 2 = 1,600). If the square footage exceeds 1,600, additional circuits are needed. Finally, the number of appliances that are cord-and-plug-connected may necessitate more circuits to prevent nuisance tripping.
When installing receptacle outlets for countertops, wall countertop spaces and island and peninsular spaces, see the requirements in 210.52(C)(1) through (C)(5). These were the only questions I had time to answer at the meeting. I hope electricians will benefit from the information in this article.
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.