240 Amp Subpanel Hooked To A 40 Amp Breaker - Electrical - Page 2 - DIY Chatroom Home Improvement Forum


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Old 02-20-2011, 11:22 AM   #16
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240 Amp subpanel hooked to a 40 amp breaker


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Originally Posted by a7ecorsair View Post
Are the 12 breakers equally divided between the two sides of the sub panel - 6 on each side?
It doesn't matter which side the breakers are on, it depends which phase they are on. if all of your heavy loads are on the same phase you are only over loading 1 side of the 40a main breaker thus causing it to trip, loosing power to the entire panel. I agree with COLDIRON, you need to take some load readings you may be able to solve you problems by balancing the panel.

Typically a 12 circuit panel A phase would be ccts 1,2,5,6,9,10 B phase 3,4,7,8,11,12

hope is helps

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Old 02-20-2011, 11:40 AM   #17
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240 Amp subpanel hooked to a 40 amp breaker


since we have pipe between boxes, we could upsize the wire. what size pipe is it? and we'll look up how big of wire you can get in it.
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Old 02-20-2011, 12:19 PM   #18
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240 Amp subpanel hooked to a 40 amp breaker


[quote=dhubz;594370]It doesn't matter which side the breakers are on, it depends which phase they are on. if all of your heavy loads are on the same phase you are only over loading 1 side of the 40a main breaker thus causing it to trip, loosing power to the entire panel. I agree with COLDIRON, you need to take some load readings you may be able to solve you problems by balancing the panel.

Typically a 12 circuit panel A phase would be ccts 1,2,5,6,9,10 B phase 3,4,7,8,11,12

hope is helps[/q
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Old 02-20-2011, 01:39 PM   #19
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240 Amp subpanel hooked to a 40 amp breaker


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It doesn't matter which side the breakers are on, it depends which phase they are on.
Well, keep in mind the level of experience of the OP.
On my GE panels (3) and my Sq D (1), each vertical adjacent breaker is on the opposite leg (phase if you prefer) so, therefore, if the breakers are evenly divided between the two sides they will be evenly divided between the two "phases". Circuit numbering may be a whole different story.
Since the OP's sub has room for 12 breakers I made an assumption that there are two columns but without seeing a picture of the panel, we don't know....
I would suspect that some of the circuits are loaded high enough to not trip the individual breakers but in combination, they would exceed the 40 amp limit.
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Old 02-22-2011, 06:35 AM   #20
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240 Amp subpanel hooked to a 40 amp breaker


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Originally Posted by a7ecorsair View Post
There is your problem. You have 12 - 20 amp 120 volt circuits drawing against one 240 volt 40 amp breaker. This 2 pole breaker can supply 40 amps to each 120 volt bus. If the 12 circuits were perfectly divided between the two bus bars and each drawing less than 40 amps the breaker won't trip but as soon a either side exceeds its 40 amp load, the breaker will trip and you will lose both sides.
Are the 12 breakers equally divided between the two sides of the sub panel - 6 on each side?
Yes they are and I know you are right. I spoke to an electrician. He said upgrade to 60 amp breaker with #6 wire.
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Old 02-22-2011, 06:38 AM   #21
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240 Amp subpanel hooked to a 40 amp breaker


Quote:
Originally Posted by a7ecorsair View Post
Well, keep in mind the level of experience of the OP.
On my GE panels (3) and my Sq D (1), each vertical adjacent breaker is on the opposite leg (phase if you prefer) so, therefore, if the breakers are evenly divided between the two sides they will be evenly divided between the two "phases". Circuit numbering may be a whole different story.
Since the OP's sub has room for 12 breakers I made an assumption that there are two columns but without seeing a picture of the panel, we don't know....
I would suspect that some of the circuits are loaded high enough to not trip the individual breakers but in combination, they would exceed the 40 amp limit.
What's OP mean and what's phase mean?
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Old 02-22-2011, 07:45 AM   #22
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240 Amp subpanel hooked to a 40 amp breaker


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since we have pipe between boxes, we could upsize the wire. what size pipe is it? and we'll look up how big of wire you can get in it.
I think it's 1"
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Old 02-22-2011, 08:59 AM   #23
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240 Amp subpanel hooked to a 40 amp breaker


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Originally Posted by msgrappling View Post
What's OP mean and what's phase mean?
OP = original poster

Phase, although improperly used in regards to a single phase system, refers to a hot leg from the transformer. You have 2 incoming hots and a neutral in a 120/240 volt single phase 3 wire system.
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Old 02-22-2011, 09:06 AM   #24
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240 Amp subpanel hooked to a 40 amp breaker


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Originally Posted by msgrappling View Post
What's OP mean and what's phase mean?
OP is original poster - you. It is just a short cut to refer to the person whom started the tread.
Phase - without have a long discussion on this, your power coming in is 240 volts but it is divided in half by the neutral wire so you have 2 separate 120 volt buses that single pole breakers can be attached to. If you attach a two pole breaker, on side will connect to one bus and the other side to the other bus giving you 240 volts at the terminals.
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Old 02-22-2011, 01:11 PM   #25
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240 Amp subpanel hooked to a 40 amp breaker


Assuming that it is 1" EMT(measure inside) and that you use THHN you can get 4 -4ga or 3 -3ga conductors in the pipe by code(close to the number you can get in their physically) If you undersize your neutral and add the required EGC(ground) you could supply 90a (next size breaker)

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