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Old 10-23-2007, 08:18 PM   #1
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Using Main Breaker in sub panel


Hi folks. Here's the goods-I have a seperate main disconnect and a sub-panel. 2 of the 20 circuits in the sub are being used as main lugs. This particular sub panel can be used as a main (using the supplied breaker and knockout at the top of the box) or a sub-panel which is its current state.

Is it OK to run my sub panel hot feeds to the main disconnect breaker at the top of the sub-panel which would give me back 2 circuts?

Thanks all for your time!

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Old 10-23-2007, 08:27 PM   #2
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Using Main Breaker in sub panel


Where is the sub?

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Old 10-23-2007, 10:22 PM   #3
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Using Main Breaker in sub panel


I would take the existing double pole breaker that is now being used as the main breaker and replace the factory main breaker with it. I am assuming that the factory main must be too large amperage for the feeder conductors and that is why it was not used.
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Old 10-24-2007, 05:51 AM   #4
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Using Main Breaker in sub panel


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I am assuming that the factory main must be too large amperage for the feeder conductors and that is why it was not used.
The main breaker in the sub-panel can be anything. it is not possible to be too large, as long as the main disconnect is sized properly.
The "main breaker" in the sub is NOT protecting the feeder cable, the main disconnect is (assuming it's a breaker).
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Old 10-24-2007, 06:23 AM   #5
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Using Main Breaker in sub panel


Of course you are correct about the main disconnect not protecting the line side, however, what could be the disadvantage of changing the main in the sub panel (if you already have the other DP breaker)?

Assuming that the factory main is 100 amps at the sub panel and assuming that the feeder for the sub panel is smaller than 100 amp (otherwise there would not have been a purpose behind adding a double pole breaker as a main), then on a over current (short or otherwise) the breaker back at the main distribution panel would trip before the 100 amp main at the sub panel (assuming that the DP breaker feeding the sub panel is smaller than 100 Amp).

Now if both the Main distribution panel and the sub panel are located near each other, there is no problem or inconvenience, but if the two are located a good distance apart, then you have to go from one panel to the other.

Personally, when and if a main trips and turns off a panel, I want that main to be in the panel that it is being turned off, because that is the panel that I will be working in.

Just a personal preference.... Safe either way.
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Old 10-24-2007, 04:19 PM   #6
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Using Main Breaker in sub panel


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Personally, when and if a main trips and turns off a panel, I want that main to be in the panel that it is being turned off, because that is the panel that I will be working in.
HUH?????

First off, the main will NOT trip. Sorry, but it won't. At least it is EXTREMELY unlikely to EVER trip a main breaker.

Second, what does it matter where the smaller breaker is? So, if the feeder breaker trips you have to walk to the main panel to re-set it. This is just my own logic I guess. I don't use drive-up windows either.
If you are working in a panel you would turn off that breaker anyway.

Sorry, I'm not flaming, I just do not see the logic.
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Old 10-24-2007, 05:21 PM   #7
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Using Main Breaker in sub panel


Yes, I understand that your not flaming . The difference about where the breaker trips can be important at times.

If the sub panel is located in an apartment (lets say) and you don't have access to the main distribution equipment, it might make a difference.

Like I said, just my personal preference, just like my preference to not turn off the main when working in a panel.

I guess that I am not as lucky as you are because I do come across main breakers that trip. But then again I also use drive up windows .

Whatever floats your boat.

But I guess this whole thread has gone off subject and point.
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Old 10-24-2007, 06:09 PM   #8
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Using Main Breaker in sub panel


The only time I have seen a main trip is: 1) In a commercial setting, or 2) when the main buss stabs were burning up.

I am of the STRONG opinion that any tenant must have access to ALL their circuit breakers. I see this compromised all too often, but your scenario is valid.

I just now realized you are also an electrician. The "turning off the main" comment was more DIY related. "We" all work in live panels but I never recommend a DIY do the same.
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Old 10-25-2007, 07:01 PM   #9
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Using Main Breaker in sub panel


Hi again folks. Thanks for the responses. It's nice to see the subject getting honest debate. The main disconnect is rated at 100 amps, the proposed sub breaker is also 100 amps in a 100 amp box. I guess it all boils down to this. Can I have 3 breakers on a circuit? I just don’t want to remove the current main disconnect but I would like to reclaim 2 circuits in the sub. Thanks again for everyone’s attention to this post.
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Old 10-25-2007, 07:03 PM   #10
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Using Main Breaker in sub panel


What you suggest is no problem.
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Old 10-25-2007, 07:09 PM   #11
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Using Main Breaker in sub panel


Wow-now that was fast! Thanks for the advice. The current disconnect is 6 inches to the right of the sub. Being a DIY and all, I do find quite a peace of mind that I can de-energize the entire panel while working in it. Thanks again.

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