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Old 09-11-2012, 11:36 AM   #1
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Changing Main Breaker box (or is it Main Lug box?)-


Hi all,

First of all, let me say thanks as I have frequently came here as a visitor to find answers to my various DIY issues of the day.
However, today, my question is left unanswered from searching the forum, hence my posting for your help.

I live in a town house that is one of 10 units. Electricity arrives outside in the DWP meters with a 90A main breaker circuit there for my unit. Inside the unit, we have a 12 space / 24 circuit main lug that connects all circuits. The box is 30 years old and has no door, leaving all cables visible.

As I understand that finding a cover for an unknown box is a task not worth spending time on, I decided to change the box for an inexpensive Square D 125A box with approximately similar height and width. (HOM1224L125TC)
Square D also offers similar box with a 100A main breaker for $20 more (HOM1224M100TC) which would give us the convenience of having a main breaker inside the house instead of having to go out in the main DWP box to do so (for example if we need to change a breaker, leave the unit empty for a while, etc).

My question is as follows: if I buy the 100A main breaker box, will I be able to find a 90A main breaker for it so that should the main breaker need to trip, it would trip inside and not outside? (it seems a bit pointless to me to have a 100A breaker on a 90A line )

Thanks for your help!

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Old 09-11-2012, 01:47 PM   #2
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Changing Main Breaker box (or is it Main Lug box?)-


The breaker on the inside panel will be a disconnect only and you can use the 100 amp breaker.

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Old 09-11-2012, 02:28 PM   #3
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Changing Main Breaker box (or is it Main Lug box?)-


Hi rjniles,
Thanks for the reply.
So if it's just a disconnect, is it just a manual switch then, with no automatic tripping?
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Old 09-11-2012, 02:36 PM   #4
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Changing Main Breaker box (or is it Main Lug box?)-


It could, under the right circumstance trip first, but in your case will just be used as a disconnect.
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Old 09-11-2012, 02:50 PM   #5
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Changing Main Breaker box (or is it Main Lug box?)-


I get it. Thanks.
If I sell the house down the road, it is in compliance with code to have this installation (a 100A breaker behind a 90A one) or will I need to change it back to a main lug box?
(I am in California, if it matters, where NEC2008 is used)
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Old 09-11-2012, 03:44 PM   #6
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Changing Main Breaker box (or is it Main Lug box?)-


Quote:
Originally Posted by pyheme View Post
I get it. Thanks.
If I sell the house down the road, it is in compliance with code to have this installation (a 100A breaker behind a 90A one) or will I need to change it back to a main lug box?
(I am in California, if it matters, where NEC2008 is used)
It is compliant under any version of NEC. I cannot imagine any local amendment that would superceed but you need a permit/inspection and the AHJ will tell you.
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Old 09-11-2012, 10:27 PM   #7
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Changing Main Breaker box (or is it Main Lug box?)-


OK - thanks. That's very helpful! Thank you all.
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Old 09-11-2012, 11:29 PM   #8
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Changing Main Breaker box (or is it Main Lug box?)-


The only quirk I am not sure about your area but you say Town house with 10 units I rather have this done by electrician so don't be suprised if the inspector say it have to be done by electrician.

Merci,
Marc

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