Can I use a 200amp panel as a 125amp subpanel?

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Old 06-29-10, 04:51 PM
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Can I use a 200amp panel as a 125amp subpanel?

I want to replace my subpanel. I have a 200amp main panel but most of my house circuits are in an old Zinsco 125amp subpanel that is mounted directly next to the main panel in the basement. The main panel is much newer so I'd prefer not changing it. For a new subpanel, I priced a 125amp SquareD QO panel (32 slot) but it's MUCH cheaper to buy a SquareD QO 200amp 30 slot panel instead (QO3040M200VP is $160. versus $400 for the QO132M125). This 200amp panel is one of SquareD's "value pack" panels.

Inside my main panel, there is #2 copper leaving the 125amp breaker that feeds the subpanel.

My question: can I use a 200amp panel (with it's pre-installed 200amp main breaker) as the subpanel given that it's first being protected by the 125amp breaker in the main panel?

Here is what my current setup looks like:

MAIN PANEL (200amp) with these breakers:
125 double (to subpanel)
60 double (to shop)
50 double breaker (to garage)
40 double (sauna)
40 double (hot tub)
20 double (two small wall heaters)
20 single (microwave)
15 single (lighting)
15 single (lighting)
(there are separate subpanels inside the shop, garage and sauna buildings)


SUBPANEL (125 amp) with these breakers:
40 double (kitchen range)
30 double (well pump)
30 double (dryer)
30 double (water heater)
20 double (bathroom heater)
20 single (lighting)
20 single (lighting)
30 single (dishwasher)
30 single (refrigerator, disposal, venthood)
20 single (lighting)
20 single (washer)
20 single (boiler furnace)
20 single (lighting)
15 single (lighting)
15 single (lighting)
15 single (lighting)
15 single (lighting)

Thanks very much!
 

Last edited by fromhollywood; 06-29-10 at 07:22 PM.
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Old 06-29-10, 05:06 PM
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You can use the panel, but I would put a smaller main in there that's less then the subpanels disconnect to prevent any future confusion.

Others will chime in.
 
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Old 06-29-10, 06:44 PM
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Originally Posted by fromhollywood View Post
My question: can I use a 200amp panel (with it's pre-installed 200amp main breaker) as the subpanel given that it's first being protected by the 125amp breaker in the main panel?
Short answer is Yes. Using a panel that is rated greater than what is being fed into it is just fine. You can feed the wires into 200 amp as a disconnect since that is all it will be since the wires and panel are protected by the 125 amp breaker.

Originally Posted by fromhollywood View Post
Inside my main panel, there is #2 copper leaving the 125amp breaker that feeds the subpanel.
This is OK as long as it is feed with a 75 degree wiring method. (THHN/THWN etc)
 
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Old 06-30-10, 10:22 AM
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Originally Posted by fromhollywood View Post
Inside my main panel, there is #2 copper leaving the 125amp breaker that feeds the subpanel.
Do you also have an insulated #2 neutral and bare or green #6 ground? If not they will need to be added and the neutral isolated in the new sub. Many old subpanels were installed with only three wires and that needs to be upgraded to four for new subs.

can I use a 200amp panel (with it's pre-installed 200amp main breaker) as the subpanel
Yes.

40 double (kitchen range)
30 double (dryer)
No problem if these are four wire circuits, however if these have old three-wire circuits they will either need to be moved to the main panel or rewired with four-wire circuits to continue to be fed from the sub.
 
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Old 06-30-10, 10:53 AM
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Thanks for the replies so far guys. I appreciate your comments.

I like hearing that you're all saying it's ok to use this 200amp inexpensive panel for my 125amp subpanel but I'm a little confused in why its ok. Isn't putting a 200amp panel (with it's factory installed 200amp breaker) inviting some future owner of this home to think they can start loading up this subpanel beyond the 125amp that it should have? I know there is a 125amp breaker feeding it (from the main) but this new subpanel will likely have a sticker on it saying it's rated for 200amp. HotInOKC suggested replacing the 200amp breaker with a 125 so it would match the 125 in the main. That makes sense to me but are you guys saying that's not necessary?

ibpooks: I will check into the wires feeding the sub and also for the kitchen range and dryer. It's interesting you noticed those two particular circuits because those two are the only ones that occasionally trip the breakers. I don't like relying on Zinsco breakers any longer so that's why I want to replace this subpanel.

(Since my posting yesterday, I noticed a new finding----the Zinsco subpanel has a 100amp main breaker even though the newer main panel is feeding the Zinsco sub with a 125amp breaker).
 

Last edited by fromhollywood; 06-30-10 at 11:20 AM.
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Old 06-30-10, 11:20 AM
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Originally Posted by fromhollywood View Post
but I'm a little confused in why its ok.
200A is the maximum rating, you are free to use if for less. Sort of like your truck can take 2000 lbs, but there's no problem putting 500 in there.

That makes sense to me but are you guys saying that's not necessary?
It is not necessary. The 125A breaker provides overcurrent protection for everything downstream of it, the 200A is just a convenience disconnect in this case. The main breaker in the subpanel is not even required at all.

the Zinsco subpanel has a 100amp main breaker even though the newer main panel is feeding the Zinsco sub with a 125amp breaker).
Then is actually a 100A panel. The smallest breaker in the chain determines the ampacity.
 
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Old 06-30-10, 12:19 PM
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Originally Posted by fromhollywood View Post
Isn't putting a 200amp panel (with it's factory installed 200amp breaker) inviting some future owner of this home to think they can start loading up this subpanel beyond the 125amp that it should have? I know there is a 125amp breaker feeding it (from the main) but this new subpanel will likely have a sticker on it saying it's rated for 200amp.
A smart electrician/home owner would instantly know that something was up as soon as they removed the panel cover and saw that the panel was only fed with #2 wire instead of 2/0.
However, if you like you could always put a note on the panel index stating something like: "Panel fed from house panel circuits 00 & 00 125amp".
 
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Old 06-30-10, 06:23 PM
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HotInOKC suggested replacing the 200amp breaker with a 125 so it would match the 125 in the main. That makes sense to me but are you guys saying that's not necessary?
It's not necessary and a replacement 125 amp main breaker to fit your panel would likely cost as much as the panel.
 
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Old 06-30-10, 06:55 PM
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A main breaker in the sub is not even needed. Save your money and leave things as they are.
 
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