Feed for sub panel

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daryl

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I have a customer with a full 100 amp main panel. She needs more spaces. I tried to make her understand that she needs an upgrade to a bigger panel. She only wants a 50A sub panel. Well ok then.(shes an idiot). I had told her the sub would be cheaper so thats what she wants. This panel has two main lugs that feed the main breaker. Can I put my 50A ser wire under those lugs to feed my sub panel, or do I need to put a 2 pull 50A breaker in her existing panel to feed my main lug sub panel? I am pretty sure you can. And I was told to do it when I was an apprentice.(long time ago). But now my buddy says I can't do that. I'm breaking out the code book now just wondering what you guys think? Thanks for your time!!!
 
Re: Feed for sub panel

I am guessing that the new sub-panel will be close to the existing main. Keep it withing 10 feet, enclose the new feeder in conduit, and follow the rest of the rules in 240.21(B)(1), and I think what you describe would be acceptable.

Or am I missing something about this being a second "main panel," since it comes upstream of the existing main panel's disconnecting means? I suppose it might come down to whether the existing main panel has a main breaker that serves as the main disconnecting means. In other words, it depends on where the N-G bond connection is made.
 
Re: Feed for sub panel

Do you want to add the two new conductors under the existing lugs that now contains the conductors for the 100 amp main?

If so, this would be a violation, unless the lug is rated for more than one conductor.
 
Re: Feed for sub panel

Originally posted by infinity:
Do you want to add the two new conductors under the existing lugs that now contains the conductors for the 100 amp main?

If so, this would be a violation, unless the lug is rated for more than one conductor.
And you will be increasing the available load on the service conductors by 50% (are they rated for that?) and the meter base may become overloaded.

I think you are much better putting in the 50-amp over current device to feed the subpanel.
 
Re: Feed for sub panel

can you pull one of the branch circuits in the main panel and move it to your sub thusly opening up a space in your main for your 2 pole 50a breaker
 
Re: Feed for sub panel

How do you figure it increases the load on the service conductors by 50%? Maybe the load is only 5 amps.

I don't see a big problem with what he is doing unless he is actually adding a large load. Than he should get out his pencial and do some figuring.
 
Re: Feed for sub panel

Daryl: The question I have is there going to be any additional loads? Is there an addition to the existing structure? I either one of the the?preceding is true, you must calculate the additional loads in accordance with 220.16 (2005 NEC). There is nothing wrong with adding a 50A panelboard adjacent to the existing 100A panel. If space allows, a short nipple or cable can be used between panels. If you connect the the?power for the second panel on the line side of the 100A service breaker, the conductors to the second panel are service conductors and are not governed by the tap rules in 240.21. This means that you must install a 50A breaker in the 50A panelboard to protect the bus in the 50A panel.

If you install a 50A breaker in the 100A panelboard on the load side of the 100A Main, no additional main breaker is required in the 50A panel. The conductors on the load side of the 50A breaker in the 100A panel are now feeders and come under the tap rules in 240.21(C).
John C.
 
Re: Feed for sub panel

Yes the 50 amp sub panel will be right next to the existing main. It will have an offset nipple between them. The customer only needs one more circuit (for now) there house is pretty much maxed out on add ons (no more room inside or out). This will be for a waterfall- pond. Everything all together maybe 12 amps on a 20 amp GFCI protected circuit. Yes I usually do pull out two branch circuits in the existing panel, put them in the new one. Then I put my new 50 Apm double pull in its place to feed my %0 amp main lug -no main breaker panel. I new this was the more correct way, but always tryin to think of ways to make things easier you know, and quicker unfortunately. Thanks guys for your thoughts again.
 
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