Q. How do you determine the minimum number of general lighting and general-use branch circuits required by the NEC for dwellings?
Find the Answer
A. The minimum number of general lighting and general-use receptacle branch circuits must be determined by dividing the total calculated load in amperes by the ampere rating of the circuits used [210.11(A)].
For example, let’s say you’re trying to determine how many 15A, 120V circuits are required for the general lighting and general-use receptacles for a dwelling having floor area of 1,500 sq ft, exclusive of an unfinished cellar not adaptable for future use [Example D1(a) in Annex D]?
Step 1: Determine the total VA load.
VA = 1,500 sq ft x 3VA per sq ft [Table 220.12]
VA = 4,500VA
Step 2: Now solve for the amperes.
I = VA ÷ E
I = 4,500VA ÷ 120V
I = 38A
Step 3: Determine the number of circuits.
Number of Circuits = 38A ÷ 15A
Number of Circuits = Three 15A or two 20A
Note: There’s no limit to the number of receptacles on a circuit in a dwelling unit.
If you calculate the load based on the volt-amperes/square foot method, the wiring system must be provided to serve the calculated load, with the loads evenly proportioned among multioutlet branch circuits within the panelboard.
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