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Old 12-09-2010, 06:17 PM   #1
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Main Lug Panel at Service Entrance


My house was built in 1973, and has 100 amp service from the utility company.

At the service entrance, I have a meter, which then connects to a main lug QO panel. Their is no main breaker.

The main lug panel has two breakers, a 100 amp for the house, and a 30 amp for the pool equipment.

Is this allowed now/has it ever been allowed? It seems like I could put 130 amps of load onto the 100 amp utility lines, which would only be proper if they had 100 amp protection upstream, which from my limited understand they do not have.

Mark


Last edited by mud99; 12-09-2010 at 06:36 PM. Reason: spelling
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Old 12-09-2010, 06:33 PM   #2
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Main Lug Panel at Service Entrance


Where are the rest of the breakers for the house?

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Old 12-09-2010, 06:36 PM   #3
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Main Lug Panel at Service Entrance


On subpanels fed from either the 100 amp or 30 amp breakers mentioned above.
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Old 12-09-2010, 07:04 PM   #4
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Main Lug Panel at Service Entrance


Do you have all in one meter socket or have two seperated box next to the meter ??

And where ya located ? { once I know which state we will figure it out pretty fast}

Merci.
Marc
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Old 12-09-2010, 07:37 PM   #5
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Main Lug Panel at Service Entrance


Quote:
The main lug panel has two breakers, a 100 amp for the house, and a 30 amp for the pool equipment.


you might check to see if the 100 amp breaker is back feeding that panel and the lug connections actually feed the panel in the house.
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Old 12-09-2010, 07:50 PM   #6
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Main Lug Panel at Service Entrance


Legal if there are 6 or fewer breakers in that panel.
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Old 12-09-2010, 08:26 PM   #7
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Main Lug Panel at Service Entrance


I'm in California, it's an all-in-one panel with the meter panel on the left and a QO load center on the right

Backfeeding from the 100 amp breaker to the main lugs is a possibility, I will have to check that. Would be totally stupid and unintuitive if someone did that, but I suppose it's technically safe, except for the fact it isn't tagged and it isn't intuitive.
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Old 12-09-2010, 09:20 PM   #8
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Main Lug Panel at Service Entrance


Quote:
Originally Posted by mud99 View Post
Would be totally stupid and unintuitive if someone did that, but I suppose it's technically safe, except for the fact it isn't tagged and it isn't intuitive.
why? That allows for a single main breaker and is actually a very common installation.

your main disconnect must be labeled. If it is the 100 amp back fed, it must be labeled. If it is the two breakers, they both must be labeled.
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Old 12-10-2010, 09:40 AM   #9
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Main Lug Panel at Service Entrance


I just checked - the panel is not being backfed through the 100 amp breaker.

Here is a pic of the install. The 30A breaker on left is for the pool subpanel, the 100A breaker at right is for the inside panel.

No main breaker.
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Old 12-10-2010, 09:42 AM   #10
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Main Lug Panel at Service Entrance


I guess I shouldn't have called this a "main lug" panel, since their are no lugs, I was describing it from memory.
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Old 12-10-2010, 10:46 AM   #11
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Main Lug Panel at Service Entrance


Very common setup even today.
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Old 12-10-2010, 10:57 AM   #12
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Main Lug Panel at Service Entrance


yes, there is a main breaker, or more correctly, 2 main breakers. That is a meter main combo. Very different than a separate MLO panel.

so, to your question: yes, theoretically you could draw 130 amps through the meter and service drop wiring. Realistically, it will never happen. Especially in a residential situation, you rarely fully tax a service. In fact, the service drop wiring is allowed to be slightly undersized because of that.
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Old 12-10-2010, 12:08 PM   #13
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Main Lug Panel at Service Entrance


Can't believe this is allowed, it seems wrong. Just because most people don't fully tax their service doesn't mean it should be undersized.

So would it be up to code for me to add another 100 amp breaker for another subpanel to this? Because that would bring me up to about 230 amps potential fault current, which IMO does not sound "slightly" oversized anymore.
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Old 12-10-2010, 02:47 PM   #14
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Main Lug Panel at Service Entrance


I'm not seeing where you could add another breaker.

Does the literature on the cover give any limitations as to quantity and ampacity of breakers?
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Old 12-11-2010, 04:50 PM   #15
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Main Lug Panel at Service Entrance


Read the labels.

Probably a 200A meter main.

I don't see very many >100A breakers that fit a QO bus. Having only two slots that accept breakers that are only available up to 100A tends to inherently limit the load to 200A.



As far as never really taxing a service entrance... that's generally true, but I had to heat the 2-story 4-bedroom project project house with electricity for a couple days (ran out of oil at a very inconvenient time) and did manage to come close - electric oven, two clothes dryers (there happened to be a spare), and six 1500W space heaters. 100A service.

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