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jeffjohnson1 09-29-2008 01:04 PM

main breaker panel terminology question!
I am trying to replace a Square D 200A main breaker panel that is in my new home (30 space) with one that has 40 spaces. I see that some are listed as 30/40 (30 spaces/40 circuits) and some are listed as 40/40 (40 spaces/40 circuits). What does this mean. My current situation is this: Builder screwed up and put a 30 space box in instead of the 40 space box that should be there (actually, I probably should have had a 400A service, but we really don't have much demand - gas heat and cooking, gas hot water, etc....though I may want to add more later). To remedy this situation, he installed a 20 space sub-panel powered by a 100A breaker he stuck in the bottom of the 200A/30 space panel. Most of the circuits are "light", in other words, there is one thing on each circuit and I could make out with more load on each circuit (i.e. garage lights on one circuit by themselves, garage receptacles on one circuit by themselves, spare bedroom on one circuit, etc....). I have tried to put "tandem" breakers in and I guess that this box was not built to accept tandems since they won't fit and my local electrical supplier says that Square D made some residential boxes like that. I don't think that the sub-panel will accept them either. Is it possible to just replace the buss bars in the panel with ones that will accept the tandem breakers? This seems to be the simplest thing to do. I have a double-throw transfer switch installed for a generator so killing power to the main panel is easy and won't require the power company to do anything. No danger either.
Anyhow, any info or suggestions is greatly appreciated.

handyman78 09-29-2008 02:07 PM

200a is a standard in most average sized homes today.

30/40 means 30 full-size spaces, 40 circuits. 40/40 is 40 full size spaces for 40 circuits.

The 30/40 would need to use 10 tandem breakers (half size or 2 in one) to utilize the full 40 circuits. The overall size of a 40/40 allows for ease in wiring and a nicer looking install. To save money many home builders seem go with the 30/40 but this is not an ideal situation. On the inside cover of the 30/40 the label will show where the tandem breakers need to fit. The buss bar is part of the entire panel and is not usually changed. The ground and neutral can often be though.

jeffjohnson1 09-29-2008 02:15 PM

Thanks for the reply. I don't know which panel I have but I would guess that it is a 30/30 and not a 30/40, since I don't remember seeing any "diagrams" on the inside door other than the "list" for numbering breakers. I will look when I get home this evening. I think that the easiest thing to do would be to, instead of installing an entirely new panel, which would involve re-running all of the wires to the double-throw and the sub panel, to install a new set of buss bars (if this is even possible) turning my existing panel into a 30/40. Does anyone know if this is possible? Can I buy such parts from Square D?

handyman78 09-30-2008 08:04 AM

Some companies panels may have the ability to swap out the insides- you would have to get the model number and check with a SquareD distributor to see if it is possible.

On the other hand- considering supply and demand- the price of a swap might be more than getting one new from a depot type store. I just replaced my old Murray panel 20/30 with a new Siemens 40/40 a week ago. A value pak which included 8 breakers cost 140.00. Labor was all mine of course. SquareD for a 40/40 was $209. with only the 200a main included.

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