Does a 3 phase 60 amp panel provide 60A?

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jonathan

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Does a 3 phase 60 amp panel, 208/120Y, that has nine, 20 amp circuit breakers, provide 60 amps? My supervisor states that each phase of the three multiwire branch circuits provides 60 amps for a total of 180 amps. All of a sudden, my brain is vapor locked about this. Thanks in advance,guru's.
 
60 amps

60 amps

60 amps of 3 phase power, 60 x 3 or 180 amps of single phase, or if you prefer 21.6 kw
 
I vote with calculating VA and describing that.

You have a 60A 208/120Y panel.

You can get 60A on each leg.

This gives you 60*208*1.732= 21.6 KVA.

You could feed a total of 180A of line-neutral load (180 * 120 = 21.6 KVA). (That is 60A from leg A to neutral, 60 from B to neutral, 60 from C to neutral)

Or you could have a total of 103.9A of line to line load (208 * 103.9 = 21.6KVA) (That is 34.6A from leg A to leg B, 34.6 B to C, 34.6 C to A)

Or you could have a total of 60A of three phase load.

-Jon
 
Not strictly so:

Not strictly so:

You can think of, loosely, a total current of 180A. Fully loaded and balanced, you would measure 60A in each line, however since these currents are 120 deg. out of phase with each other, their sum is 0A, not 180A.

As Hunk says, you can add apparent power in KVA for a total of 21.6KVA because power is a scalar quantity. This is strictly correct.
 
This is not a system of 180A. It is (3) legs of 60A each.
How you connect them is your business but, you cannot have more than 60A per conductor.
 
Just nit picking:

Just nit picking:

hardworkingstiff said:
That's a loaded statement. Trying to get something going? :D
Click to expand...

Just trying to explain why the neutral current in a balanced system is zero. One could be misled into thinking it is thrice the line current or in this case 180A.
 
hardworkingstiff said:
That's a loaded statement. Trying to get something going? :D
Click to expand...
Hard worker,
Why do you think that statement is loaded? If you add them together electrically and the pf is the same, you get zero. For once I agree with rattus.
 
jonathan said:
. . . each phase of the three multiwire branch circuits provides 60 amps for a total of 180 amps.
Click to expand...
It would be a good thing to break yourself of the habit of thinking in these terms.

Let me put it another way: it is not always correct to add amps to amps, and to express the results in amps. You need more than just the single word, “amp.” What you have in your 60 amp, three phase panel is (1) “60 amps of current with a phase angle of zero degrees,” and (2) “60 amps of current with a phase angle of 120 degrees,” and finally (3) “60 amps of current with a phase angle of 240 degrees.” This does not give you a “total of 180 amps,” but rather a total of 0 amps, as others have said.

In this case, and only because you picked a simple set of loads (all single phase, all 20 amps), by the providence of the related mathematics, you can indeed serve 180 amps worth of single phase loads, and indeed the number 180 is three times the number 60. But that won’t work out if any of the loads are single phase 208 volts, or if any of the loads are three phase. The only way to be certain you get the math right every time is to convert to VA, then do the additions, then convert back to amps as the very last step.

bob said:
Hard worker, For once I agree with rattus.
Click to expand...
So do I, but I’m not at all sure it is the first time. :grin:
 
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rattus said:
Just trying to explain why the neutral current in a balanced system is zero. One could be misled into thinking it is thrice the line current or in this case 180A.
Click to expand...

It may be balanced, but what if they are all computer loads and the harmonics are high, the current on the neutral would not be zero :)
 
bob said:
Hard worker,
Why do you think that statement is loaded? If you add them together electrically and the pf is the same, you get zero. For once I agree with rattus.
Click to expand...

I did not disagree with Rattus, I just said it's a loaded statement.

The OP was asking about single-phase loads on a 3-phase panel. If all three of the legs were pulling 60-amps @ 120-volts, you would indeed have 180-amps @ 120-volts of power usage.

Rattus' statement went off course in that he was adding the currents vectorially and came up with zero. That would be the neutral current (discounting any harmonics). The power consumption would still be 180-amps @ 120-volts. AKA 21.6KVA
 
Steering off course a little

Steering off course a little

Ok,

Let's say you load this panel up with three 208-volt 1-phase circuits pulling 30-amps each. You balance the loads equally between AB, BC, CA.


How much current on A?
How much current on B?
How much current on C?
 
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