120V vs 240V power

120V vs 240V is the choice of supply voltage for a workstation's wall circuit. Common 120 V circuits are 15 A or 20 A, on NEMA 5-15 and 5-20 receptacles, and a NEMA 6-20 serves a 240 V, 20 A circuit. Watts are volts times amps, so one breaker passes twice the power at 240 V. ABB quotes the 2014 National Electrical Code requiring a branch circuit breaker rated at least 125 percent of a continuous load, one lasting three hours or more. That caps continuous draw at 80 percent of the breaker.

That is about 1,440 W continuous on 15 A at 120 V and 1,920 W on 20 A. Vertiv's Geist table rates a NEMA 5-15R at 12 A and a 5-20R at 16 A. Power supplies can derate on low line. Supermicro's SYS-741A-T lists a 2200 W unit at 1200 W on 100 to 127 V, against 1800 W at 200 to 220 V and 2090 W at 230 to 240 V, and a 1200 W unit at 1000 W on 100 to 127 V.

On 120 V, budget the lower of the supply's low-line output and the circuit's 80 percent limit, and move a load above that to 240 V.

Sources

Last verified October 30, 2026.