Minimum Number of Branch Circuits Required for one-Family Dwellings.

 Section 210.11 contains provisions for determining the minimum number of branch circuits, including the requirements for small-appliance branch circuits, laundry branch circuits, bathroom branch circuits, and garage receptacle circuits.

Per 210.11(B), the required branch circuits shall be evenly divided across the branch-circuit panelboard. In addition, branch-circuit overcurrent devices and circuits need only be provided for connected loads. Any future loads need not be considered. See 210. 11 (A through C).

To find the required number of circuits for the lights and general-purpose receptacles, first, determine the current for the lighting and receptacle circuits. To find the current, multiply 3 VA/sq ft by the square footage of the dwelling. This is the total load in volt-amps. Divide the total volt-amps by the voltage, which is usually 120 V. This determines the current for the light and receptacle circuits. The current is then divided by the size of the overcurrent protective device, which is usually a 15 A or 20 A circuit breaker, to determine the required number of circuits. If the answer comes out to be a decimal, always round up to a whole number for example, how many 20 A, 120 V circuit breakers are required for a 2100 sq ft dwelling?

Step 1: Number of circuit breakers = 3 VA/sq ft x area of the dwelling
                                                                                   Voltage

Then = Sum of Step 1 is divided by the circuit breaker rating.

In our example :           

3 VA x 2,100 = 6,300 / 120 = 52.5

Next, 52.5 is divided by the branch circuit rating: 52.5 / 20 = 2.625 and you can’t have .625 of a circuit so you would round this to (3) circuit breakers needed.

Note: This has nothing to do with the required additional branch circuits as described in 210.11(A) through (C).