Minimum Number of Circuits
Minimum Number of Residential General Lighting Circuits
The calculation to determine the minimum number of required general lighting
circuits is easy to perform yet seems incorrect.
Here's how it works.
Square feet of a dwelling unit based on outside dimensions times 3 VA/sq. ft.
divided by 120 volts,
then divided by 15 amps if the circuits are to be 15 amp,
or divided by 20 amps if the circuits are to be 20 amps.
Example:
1600 square foot house X 3 VA/sq.ft. equals 4800VA divided by 120 equals 40
amps.
Then if the circuits are to be 15 amp, 40 divided by 15 is 2.66 round up always
which leaves three circuits for a 1600 sq. ft. house.
(You can't install .66 of a circuit.)
Then if the circuits are to be 20 amp, 40 divided by 20 is 2 even
which leaves two circuits for general lighting in a 1600 sq.ft. house.
This certainly seems like too few, but it is the NEC.
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