For electrical panels / systems with three phase electricity (red, yellow, blue) ~220/127. When using line to line we get 220 V is this considered single phase system or three phase?

I know three phase devices such as motors use all three phases together, this is clearly three phase and we use three phase formulas for calculations, but what about when using three phase system line to line? What formulas do we use for apparent power calculations?

Also if a circuit breaker is 20 A for each phase, and I am using line to line wiring, does this makes my maximum amps usage 40 A or still 20 A?

  • 2
    \$\begingroup\$ "Two phases line to line" sounds like the American split phase system, they are taken from ONE phase of a 3ph system (and centre tapped). I think you need to clarify what you're really asking. \$\endgroup\$ Jun 25 '18 at 10:09
  • \$\begingroup\$ closer to 190V is that really is a balanced 3 phase system. \$\endgroup\$
    – Jasen
    Jun 25 '18 at 10:13
  • \$\begingroup\$ @Jasen 220/127, edited the question, thanks \$\endgroup\$
    – ahmed
    Jun 25 '18 at 10:14

What is described appears to be single-phase loads connected to a three-phase supply. If the current capacity for balanced, three-phase use is 20 amps, that is all that can be drawn by a single-phase load. You can not safely connect any combination of single-phase loads that causes any of the three individual phase currents to exceed 20 amps. If the three phase currents are not equal, the safe the maximum kVA will be less than the rated kVA of the supply.

There is nothing wrong with loading the supply with single-phase loads that do not result in a balanced three-phase load, but that is not the optimum use of the generation, transmission and distribution system. Since you are presumably being charged for actual power used regardless of balance, the supplier may object because your imbalanced usage limits what can be sold to other customers.

... what about when using three phase system line to line? What formulas do we use for apparent power calculations?

When the load is not balanced, the apparent power can be calculated as the sum of the apparent powers of the individual loads. If necessary, represent the supply as three, wye-connected, sources.


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