Forsingle-phase supply, apply the rule of thumb wherein the ampacity of a circuit breaker should be 125% of the circuit connected to the CB (125% or 1.25 x load current). In a three-phase supply, you can use the same formula as the single-phase but with the three-phase power formula — √3 (1.732). Step 4. Forexample, in a 400A, single-phase, 120/240V parallel run, Phase A could be composed of two 3/0 copper conductors in parallel and Phase B composed of two 250 kcmil aluminum conductors in parallel with the neutral being two 3/0 copper conductors. TransformerSize Calculator. When sizing a transformer, you need to know the kilovolt-amps (KVA) that your machine requires. This tool will allow you calculate the KVA that you need. This tool only evaluates common voltages for North America (ie. 24v, 120v, 208v, 240v, 480v, and 600v). Firstconsider if the breaker was connected to a balanced 3 phase load with 200A per phase. The power (assume 208V-3ph) would be 200A*208V*1.732=72kVA. Now consider the same breaker with 200A line-to-neutral would be 200A*120V=24kVA per phase, times 3 phases=72kVA. 200Amps on each phase is 72kVA whether it is a 3 phase load or Ifyou have a piece of equipment that draws 80A, then you can calculate the relative size of the required power source, which is 10kW (80 ÷ 8.33). By using this same procedure but inserting the respective single-phase voltage, you get the following single-phase constants, as shown in Table 1. 3-Phase Calculations iAEF.

how many amps in 3 phase power