30A subpanel

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elecmen

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Electrician
Is there a max number of circuits that can be fed from a 30A sub panel? I'm thinking a max of 2 circuits. Is thera a limit per code?
 
What infinity said but assuming it's a 3 phase panel I'm hoping it could handle more than 3 circuits. Otherwise, why are you installing one? On a related note, if you can only max at 2 circuits, you're going to be having problems because that means that one of the phases is overloaded.
 
If you were to run a 120/240 single phase feeder to a 12 circuit panel with 12 fixed 2 amp loads connected to individual circuits you would only pull 12 amps on each feeder conductor regardless of what size breaker may be on each individual branch circuit. I know it is kind of a rare application but not impossible. Would be more common however in industrial control equipment then in a dwelling unit.

Minimum number of circuits really depends on the load(s) supplied. If there is too much load you trip the feeder overcurrent device - this is a sign that something isn't quite right.
 
ASG said:
What infinity said but assuming it's a 3 phase panel I'm hoping it could handle more than 3 circuits. Otherwise, why are you installing one? On a related note, if you can only max at 2 circuits, you're going to be having problems because that means that one of the phases is overloaded.
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How would one of the phases be overloaded ?
 
jap said:
How would one of the phases be overloaded ?
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If you have a 30A 3-phasee sub-panel and it is fully loaded after 2 circuits, I don't know how that is possible without one phase having more than 30A on it.
 
kwired said:
Too much load, of course. :)

The thing not mentioned in OP is how much load is on each circuit.
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On a 3 phase panel with only 2 circuits, considering they are on different phases, actually one phase of the feeder would be underloaded and yet still wouldn't cause a problem.
 
ASG said:
If you have a 30A 3-phasee sub-panel and it is fully loaded after 2 circuits, I don't know how that is possible without one phase having more than 30A on it.
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I see what your saying,That is if you talking about (2) loaded 3 phase circuits but if your talking (2) single phase circuit out of the 3 phase panel then you still have 30 amp of capacity left on the remaining phase.
 
jap said:
Fully loaded and Overloaded are two different scenarios.
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I was trying to say that if he thinks his panel is fully loaded (what I thought when he said "2 circuits max" would get it to be 30A at 3 phase), it is likely overloaded. Now re-reading it, I'm thinking may be it just didn't click with him when he posted that 30A is actually 30A on each phase. But I guess we will see if he has any follow up questions/statements.
 
All this talk yet we have not clarified what any of the load(s) is. Bottom line is if we have a 30 amp feeder we can supply 30 amps per ungrounded conductor in any combination of line to line or line to neutral loads, whether it be one big load or a thousand small loads.
 
elecmen said:
Is there a max number of circuits that can be fed from a 30A sub panel? I'm thinking a max of 2 circuits. Is thera a limit per code?
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It's a single phase 120/240 4 wire sub panel feeding enterance lights to mobile home park. 1 20A 120V circuit for lights and another 20A 120V circuit for sump pump. I would like to add another 120V circuit for high water alarm.
 
elecmen said:
It's a single phase 120/240 4 wire sub panel feeding enterance lights to mobile home park. 1 20A 120V circuit for lights and another 20A 120V circuit for sump pump. I would like to add another 120V circuit for high water alarm.
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30 amps at 240 volts can supply up to 7200 VA - that is quite a bit of power for the loads you mentioned. Lets say the sump pump is 3/4 hp - it may draw up to 1500 VA worst case - really depends on the efficiency and power factor, (at 100% efficiency it should draw about 560 watts)

That still leaves you with 5700VA of capacity which can run a pretty fair amount of lights - definitely more then a 20 amp 120 volt circuit can handle - the water alarm is going to be nearly nothing load wise, will draw highest current when alarm is sounding or when any battery system is charging at a high rate, but if alarm is sounding chances are it is because the pump is not running.
 
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