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Silly and simple question for all the electrical gurus (I'm mechanical newbie)

Silly and simple question for all the electrical gurus (I'm mechanical newbie)

Silly and simple question for all the electrical gurus (I'm mechanical newbie)

(OP)
We have a single phase 480V to 240/120V transformer being fed from a Motor Control Center by two phases/legs (phase A and C)...if the only load on the transformer is 240V (say 40 Amps) do I then say that phase A has 40A and phase C has 40A? What if there is 120V load? Can this load be on only Phase A? Only on Phase C? Or a combination thereof?

RE: Silly and simple question for all the electrical gurus (I'm mechanical newbie)

The 240 V load is as you say. The 120 V loads will be on either Phase A or Phase C depending on which side of the panelboard the breaker is plugged into. Normally, we try to balance the 120 V load between the two legs. In terms of the load on the transformer, your concern would be the higher of the two legs (A or C) - the sum of the 240 V and 120 V load combined. You could, in theory, put all of the 120 V load on one or the other, but there is no reason to do that and good reasons not to.

RE: Silly and simple question for all the electrical gurus (I'm mechanical newbie)

(OP)
Thank you. So to clarify, if there is only 40A of load at 240V will the 480V side of the transformer (fed by phases A and C) see 20A on each phase or will it be split between the two (A = 10A and C = 10A)?

RE: Silly and simple question for all the electrical gurus (I'm mechanical newbie)

20 A on each leg at 480 V

RE: Silly and simple question for all the electrical gurus (I'm mechanical newbie)

480:240/120 Volts.
One half of any 240 Volt load will be seen on both primary phases, A and C.

One quarter of any 120 Volt load will be seen on both primary phases, A and C.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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