|S1ø| is the single-phase apparent power drawn by the single-phase 208V two-pole breaker load. It helps to realize that the phase-voltage magnitude used in the formula |Vp| is the voltage across the single-phase load: Now plug in the values for the voltage fed from from a two-pole breaker in a 208/120V panel. The apparent power formula for single-phase power is: Remove the '2' coefficient multiplier in your formula. Two-pole 208V loads are single-phase loads that are connected line-to-line instead of line-to-neutral, utilizing the higher 208V line voltage of the power supply instead of the 120V line-to-neutral voltage.Īnd I just want to point out that this formula (and the derivation) is for both three-phase wye AND delta connected loads. The easiest way to think about this is that two-pole breaker circuits provide power to a single-phase load (instead of a three-phase load). Why do we just use the formula P=V*I?īecause two-pole breakers are actually single-phase circuits even though they provide a higher voltage compared to single-pole breakers. My confusion comes when I calculate the kVA load for 208 single phase equipment. Some HVAC equipment and lighting items require 208 single phase power, and these 208V-single phase equipment require a 2-pole circuit from a 120/208 panel. I'll do my best to address each of your questions: If this is wrong, can someone please explain why. (We have the 2 constant instead of the 3 because we have 2 hots in 208 single phase instead of 3 hots as in 208 3-phase) Isn't the derivation for 208 single phase power (i.e., a two-pole connection derived from 3-phase service) as follows: (where Van and Ian are line-to-neutral voltages and currents respectively and Vab and Iab are line-to-line voltages and currents) So, whereas the derivation for three phase power is as follows for a Y-system: However, a 208 'single phase' connection requires two hots derived from 3-phase service.

Why do we just use the formula P=V*I? I understand this for a single pole circuit, and for three phase circuits the power equation is P= SQRT(3)*V*I. I am very confused about 208 single phase power calculations.

Hello all! I'm an electrical designer fresh out of college with 6 months of experience at an MEP firm.

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