As mentioned in NEC^® section 220.5(A), unless other voltages are specified, for purposes of calculating branch-circuit and feeder loads, nominal system voltages of 120, 120/240, 208Y/120, 240, 347, 480Y/277, 480, 600Y/347, and 600 volts shall be used.

As well, 220.5(B) addresses calculations that result in fractions of an ampere. Calculations are permitted to be rounded to the nearest whole ampere, with decimal fractions smaller than 0.5 dropped. It is important to not confuse this requirement when calculating number of units.

For example, when calculating the minimum number of branch circuits required to serve a load, it may be necessary to round up to the next whole number even if the math results in 0.4 or less.

Here are two examples which deal with rounding up for fractions of an ampere or rounding up when calculating number of units:

Example 1. Rounding up the ampacity. If the final result of a 240-volt load calculation shows a value of 84,605 VA, then to determine the ampacity, divide the VA by the applied voltage:

84,605 VA ÷ 240 V = 352.52 amps. Ok to round up to 353 amps.

Example 2. Rounding up the number of units. Determine the minimum number of 120-volt, 20-ampere branch circuits needed to supply office lighting with 100 luminaires at 60W each. Lighting is considered a continuous load, use 125% per 210.20(A).

100 X 60 W = 6,000 W

6,000 W X 125% = 7,500 W

7,500 W ÷ 120 V = 63 amps

63 A ÷ 20 A = 3.15. Must round up to four 20 A circuits since this is a measurement of units.

See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to NFPA 70.