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400 amp panel/add sub-panel #51302 04/27/05 07:24 PM
Joined: Aug 2001
Posts: 545
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aldav53 Offline OP
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Bidding a job that has a 400 amp main panel on the home with 2-200 amp subpanels next to it. I would be wiring a large garage turned into a living quarters, with A/C, water heater, range, dryer, small kitchen, and lighting. Will probably have to run a new 200 amp subpanel to it. Would I be able to put a 200 amp breaker in one of the 200 amp sub-panels to feed the 3rd 200 amp? The 2 200 amp panels are fed with 4/0 wire. But that may put it over the limit. Can I add any more panels to that 400 amp service? maybe a 125 amp?


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Re: 400 amp panel/add sub-panel #51303 04/27/05 07:52 PM
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The first question is do they even make another 200 amp breaker for you 200 amp panel. If it's a load center I'd say does not exist.

If it's a panelboard you might be able to get a sub feed breaker but what is the point? It's allready covered by the 200 in the main panel. Double lugs would be cheaper.

Before you start you really nead to figure out your loads. Then you know how big of a panel you need in the garage, if a 400 amp service is large enough, & if you can tie into the 200 amp feeder.

200 amps sounds like it's on the high side for a garage turned into living space. How many sf 1200?


Myself I like to put the larger loads in the first panel. Not saying you can't sub a sub just that it does not seem ideal. But like I said we don't know the loads and how much of the 200 is used.

Tom

Re: 400 amp panel/add sub-panel #51304 04/27/05 08:09 PM
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aldav53 Offline OP
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The garage is 1300 sq ft. I did a quick load calc and it came out to 141 amps for the load. If I were to trim back the load some, could I run a 125 amp from one of the 200 panels? What is the limit on how many sub-panels can be run off a main panel?
There is a small sub-panel in the garage now with #4 THHN run to it.


The Golden Rule - "The man with the gold makes the rule"
Re: 400 amp panel/add sub-panel #51305 04/28/05 05:31 PM
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141 amps sounds a bit high. Is the garage detached from the house? Is the garage feed with pipe? If so what size? What type of panels are used in this place?

Still don't know what the loads are in the panels.

Tom

Re: 400 amp panel/add sub-panel #51306 04/28/05 06:13 PM
Joined: Apr 2002
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caselec Offline
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I agree with Tom that 141 amps sounds high. How are you doing the load calcs?

Using the optional calculation I come up with roughly 103 amps. I don’t know how big the A/C unit is but figured around 4800va (20 amps @ 240 volts)

Curt


Curt Swartz
Re: 400 amp panel/add sub-panel #51307 04/28/05 07:03 PM
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aldav53 Offline OP
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I used the load calcs in the back of the code book. The A/C is 30 amps, there is a range, dryer, water heater, (all elec), plus the kitchen circuits and lighting.
The existing sub-panel in the garage is fed with #4 in a 1" pipe.


The Golden Rule - "The man with the gold makes the rule"
Re: 400 amp panel/add sub-panel #51308 04/28/05 07:34 PM
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caselec Offline
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Calculate the loads using 220.82.
Where are you getting the 30 amps for the A/C? You need to use the actual load of the unit not the maximum fuse/breaker size. I can’t imagine this space needing more that 2.5 - 3 tons which would be around 20 amps.


Curt Swartz
Re: 400 amp panel/add sub-panel #51309 04/29/05 12:16 AM
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aldav53 Offline OP
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Its 29.2 amps, I don't think that was max breaker size. Its a heat pump, it may have aux heat too. i'll have to check.


The Golden Rule - "The man with the gold makes the rule"

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