If you measured the current in one leg of a 3-phase load and were asked, "What is the current?"?

Question

You measured the current in one leg and it was 50 amps. What would you say if someone asked you what the current was?

Would you say:
a)50 amps
b)150 amps
c) 86.6 amps
d) none of those

Answer 1

Of course, properly balanced 3-phase currents theoretically sum to zero. For this reason, answer (b) is wrong.

The 86.6 amps of answer (c) only makes sense relative to a delta connected load, where two phasors sum at each juncture to 86.6 amps. In that case, the line current is properly 50 amps, and the phase current is properly 86.6 amps.

Otherwise, for a typical Wye connected 3-phase load, current could only mean 50 amps. In that case, both line and phase currents are 50 amps.

Answer 2

It has to be 150 amps. Each leg is drawing 50 amps and your electric bill will charge you for 150 so that is the answer.

If the loads are unbalanced in the three phases that is a problem that needs correction and that is why I say EACH leg is drawing 50.

Answer 3

One lead is not the same as a single phase. The reading you took with the CT is the current draw to the motor. Each leg will vary somewhat. Full load amps on a 480 volt, 3 phase motor will be approx. 5 amps. If you get an accurate reading of 1.5-2.0 amps it means you are using approx. 1.5 HP. Rule of thumb is 1.25 amps per HP @ 480 volts. The motor is not under full load. This is not an unusual situation.

Answer 4

50 amps. If I only measured one leg, I would have good reason to assume that the currents were sufficiently balanced for my purposes and would not be interested in anything except the per phase current.

Answer 5

a) 50 amps. Current is constant accross circuit elements in series.

Answer 6

i haft to say a)50 amps but I'm not shoe.

Answer 7

I wouldn't have a clue.