SubPanel Feeds?


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Old 12-08-08, 09:17 AM
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SubPanel Feeds?

I need to install a sub panel in my 200A service box -- it's small and there's no more room for any breakers. In fact, I don't see a way to gang up any existing breakers to create space for a breaker to feed the SubPanel. It's an older house, and they used a really small 200a service box.

Do I need breakers to feed a subpanel? can't I run straight from the screws on the main breakers to feed the sub panel? I only need 55amps of service in the sub panel, which will then feed to another cutoff box with a 20amp and 30 amp breaker in it.

With that many breakers in the line, is it ok to feed the sub panel off the main breaker in the main panel?

RES
 
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Old 12-08-08, 09:25 AM
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Originally Posted by robertesmith View Post
Do I need breakers to feed a subpanel? can't I run straight from the screws on the main breakers to feed the sub panel? I only need 55amps of service in the sub panel, which will then feed to another cutoff box with a 20amp and 30 amp breaker in it.
There are a couple of problems with your idea.

The main breaker would have to be approved for piggybacking two conductors on each terminal. It probably isn't.

Then, the conductors feeding the new subpanel would have to be sized for 200A.

Why are you proposing to feed from the subpanel to another box with breakers in it? Why not put breakers in your subpanel? That would be a normal approach.

It's a better idea to use a two-pole, 240-V breaker in the existing panel to feed the subpanel. If you size the subpanel generously, you can move breakers in the existing panel to the subpanel, and make room for the new 2-pole breaker - and still have room for expansion.

Another approach would be to replace the existing panel. You can buy a new 200-A panel with spaces for 40 branch ckt positions, plus the main.
Doug
 
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Old 12-08-08, 09:35 AM
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Still working

I have about 100' run from the main panel to the hot tub. I need the 20 and 30A breakers in a cutoff box near the hot tub for safety -- I think it has to be within 25'. I can't go straight from that box to the main panel because the main panel is full, and from what I can tell, there's not enough room to gang a few breakers together to create space for a 55A breaker to feed the small cutoff box.

So I was thinking I'd have to create a subpanel off the main box, so I could place the 55A breaker in the sub panel to feed the small cutoff box near the hot tub.

When I looked in the main panel, there's just nothing there to gang, but there are 4 breakers toggled together at the top serving as the main breaker for the service, and they have screws on them biting down on the service bus bar that the breakers all clip to. I was thinking I could use the lugs on the main breakers to feed the sub panel?

RES
 
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Old 12-08-08, 10:03 AM
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Originally Posted by robertesmith View Post
When I looked in the main panel, there's just nothing there to gang, but there are 4 breakers toggled together at the top serving as the main breaker for the service, and they have screws on them biting down on the service bus bar that the breakers all clip to. I was thinking I could use the lugs on the main breakers to feed the sub panel?
RES
This does not sound kosher. I've never heard of a 200-A panel with multiple breakers serving as the main. I suspect that there are some problems with your existing setup. I even wonder if that existing panel is actually a 200-A rated panel. What does the nameplate say?

And, no, you can't run a 50-A ckt fed directly from a 200-A main. Conductors sized for 50A have to be protected with a 50-A breaker whether they are 10' long or 1" long.
Doug
 
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Old 12-08-08, 10:54 AM
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it's a square D panel

hom20-40m200C -- rated for 200A service.

Up top there are 4 mj3690 breakers with a common trip for 200Amps

I just found a couple of 15A breakers that are singles -- I could swap them out with those breakers that put two 15A breakers on a single slot, and create space for the 55A breaker I need and run straight from there...that'd work wouldn't it?
 
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Old 12-08-08, 11:40 AM
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Originally Posted by robertesmith View Post
I just found a couple of 15A breakers that are singles -- I could swap them out with those breakers that put two 15A breakers on a single slot, and create space for the 55A breaker I need and run straight from there...that'd work wouldn't it?
OK, that sounds like it would work. Use #8 or larger wire. 55-A is not a standard breaker size. You can use a 50-A breaker for #8 copper.

What are the specific current requirements for the hot tub? This should be considered a continuous load, so the ckt has to be derated by 20%. In other words, a 50A ckt is only good for 40A.

I'm assuming the hot tube takes 120V?

The specific wiring requirements depend on whether the tub is indoors or outdoors. Please read articles 680.42 and 680.43 of the 2008 National Electrical Code. It covers the type of wiring, GFCI requirements, grounding, etc.
Doug
 
 

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