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Old 03-07-2008, 11:43 PM   #1
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Sub-Panel or Tandem Circuit Breakers?


We have an unfinished basement that we are doing some design planning to get ready to start finishing it this spring or summer. The house has a Square-D QO style electric panel with 200amp service and room for 40 circuit breakers. It currently has 9 open slots.

Given my thoughts about what we're planning to put in the basement and usage plans, I'm thinking we may need more than 9 new circuits. Looking at their website, I see that Square-D makes tandem circuit breakers. However, when I look at their Residential Products Catalog, it looks like 40 circuits is the max that this panel is rated for.

Is the 40 circuit limit a vendor spec or something driven by the NEC? I saw another post on here that mentioned the NEC2008 removing some circuit limit. I guess the buses have to have certain notches in them as well, depending on the vendor, in order to be able to accept twin/tandem/piggyback breakers?

So I guess my only option would be to have a sub-panel put in, probably using a 100amp circuit breaker in the main panel? I took the cover off to look inside and they've done a pretty good job of filling up virtually all of the lock screws on the 2 neutral bars as well as some of the screws on the ground bars. There are only two knockouts left at the top as well, so not many more cables could come in from that direction.

Dave

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Old 03-07-2008, 11:52 PM   #2
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Sub-Panel or Tandem Circuit Breakers?


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Originally Posted by dgoldsmith View Post
We have an unfinished basement that we are doing some design planning to get ready to start finishing it this spring or summer. The house has a Square-D QO style electric panel with 200amp service and room for 40 circuit breakers. It currently has 9 open slots.

Given my thoughts about what we're planning to put in the basement and usage plans, I'm thinking we may need more than 9 new circuits. Looking at their website, I see that Square-D makes tandem circuit breakers. However, when I look at their Residential Products Catalog, it looks like 40 circuits is the max that this panel is rated for.

A. The manufacter will list the max number of breaker[s] in the box and if the label say QO40401M200 [ example number ] it mean only 40 full size breaker is designed in the box only. but if say like this number OQ40301M200 that mean take 10 tandem breaker with 30 full size breakers.


Is the 40 circuit limit a vendor spec or something driven by the NEC? I saw another post on here that mentioned the NEC2008 removing some circuit limit. I guess the buses have to have certain notches in them as well, depending on the vendor, in order to be able to accept twin/tandem/piggyback breakers?

A. they did recentally lift the 42 circuit limit but it will take time for manufacter to ramp up to meet the NEC and UL requirement on this one and the Canada verison do not have any limit AFAIK [ unless someone from Canada correct me on this one ] they can go many as 80 circuit.

So I guess my only option would be to have a sub-panel put in, probably using a 100amp circuit breaker in the main panel? I took the cover off to look inside and they've done a pretty good job of filling up virtually all of the lock screws on the 2 neutral bars as well as some of the screws on the ground bars. There are only two knockouts left at the top as well, so not many more cables could come in from that direction.

A. well with bare grounding it can be bunled up two per hole but netural [ white wire ] must be it own hole for safety reason.
Dave

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Merci, Marc

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Old 03-08-2008, 12:34 PM   #3
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Sub-Panel or Tandem Circuit Breakers?


Due to the description of your situation, I would install a subpanel in the basement to serve the entire basement.

I would probably put a 100 amp with the max circuit count I could obtain. I would rather have too many circuits available than too few.

If you decide to not do so, you can drill all the holes in the breaker tub as needed that you can find room to drill. Knockouts are only for convenience (although I actually prefer tubs with no knockouts in the line of work I do). You can obtain additional ground and neutral bars if needed as well but in a SqD panel there should be at least 40 holes for neutrals in a 40 circuit panelboard. There is an add on large lug that attaches to the neutral bar for larger neutral conductors if needed as well (feeding the 100 amp panel)
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