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Old 12-13-2010, 07:15 AM   #1
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Adding subpanel vs new larger panel


If additional space is needed for more circuits (assuming there is available amps left), whats the difference between adding a smaller subpanel vs. replacing main panel with a new larger one?
If the amps are available, wouldn't it be the same either way?
I see that many responses to this type of question always seem to point to "replacement" rather than adding a subpanel.
What am I missing?
Thanks for any advice.
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Old 12-13-2010, 07:43 AM   #2
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Adding subpanel vs new larger panel


If you have enough available amperage for the circuits you intend to add, a subpanel is easier since you don't have to upgrade your main circuit breaker. There are specific rules you have to follow when installing a subpanel, particularly the ground and neutral bars MUST be isolated from each other.

What is the amperage of your current panel? You will need 2 adjacent (vertically) breaker slots to add a double-pole breaker to feed a subpanel.
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Old 12-13-2010, 07:47 AM   #3
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Adding subpanel vs new larger panel


Quote:
Originally Posted by lonric View Post
If additional space is needed for more circuits (assuming there is available amps left), whats the difference between adding a smaller subpanel vs. replacing main panel with a new larger one?
If the amps are available, wouldn't it be the same either way?
I see that many responses to this type of question always seem to point to "replacement" rather than adding a subpanel.
What am I missing?
Thanks for any advice.
I think it depends on preference and what you intend to do with the extra space in the new panel or sub. This of course assumes that your existing panel is in good shape (if it is degraded, then you should replace it).

In my case, I had a 200A main panel that was full and I needed expansion space. I opted for a subpanel instead of a new main panel because of where the main panel is located (near an outside wall under a low slope attic, making it extremely difficult to pull wires from the attic into the panel). I installed a 100A subpanel near the center of the wall in my garage, which gives me plenty of headroom in the attic to pull wires to the sub. I did have to deal with pulling the feeder from the main to the sub and also had to relocate two branches from the main to the sub to make room for the cutoff, but I only had to do it once.

Had the main panel been easier to access from the attic, I would have upgraded the panel. The difference in cost between replacing the main panel and adding a subpanel (with the associated wiring) was minimal, but the solution works better for me because I can now easily access the subpanel for whatever expansion I need to perform.
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Old 12-13-2010, 08:18 AM   #4
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Adding subpanel vs new larger panel


My service is a 200 amp with 20 spaces.
I would have to move 2 circuits to make room for a double breaker.
With a 100 amp sub panel, what size breaker and wire size should be used to feed the sub.?
60 amp with #6, or if I went to a 70amp, is it #4?
Thanks
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Old 12-13-2010, 08:37 AM   #5
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Adding subpanel vs new larger panel


What brand and model # is your main panel?
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Old 12-13-2010, 08:51 AM   #6
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Adding subpanel vs new larger panel


Quote:
Originally Posted by lonric View Post
My service is a 200 amp with 20 spaces.
I would have to move 2 circuits to make room for a double breaker.
With a 100 amp sub panel, what size breaker and wire size should be used to feed the sub.?
60 amp with #6, or if I went to a 70amp, is it #4?
Thanks
I'm using a 100A double-pole breaker as the subpanel disconnect with a AWG4 4-wire feeder to the sub (remember that you cannot bond the neutral to the ground in the subpanel; the sub must ground back through the main panel).
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Old 12-13-2010, 09:43 AM   #7
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Adding subpanel vs new larger panel


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Originally Posted by brric View Post
What brand and model # is your main panel?
Its a square D, model QOC20MG225, series L4
If I went with a 70 amp breaker, still use #4 copper?
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Old 12-13-2010, 09:43 AM   #8
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Adding subpanel vs new larger panel


Quote:
Originally Posted by clashley View Post
I'm using a 100A double-pole breaker as the subpanel disconnect with a AWG4 4-wire feeder to the sub (remember that you cannot bond the neutral to the ground in the subpanel; the sub must ground back through the main panel).
#4 copper in your instance is only rated for 85 amps, not 100.
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Old 12-13-2010, 10:56 AM   #9
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Adding subpanel vs new larger panel


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Originally Posted by brric View Post
#4 copper in your instance is only rated for 85 amps, not 100.
brric: so if i were to use a 70 amp breaker to the subpanel, should I use #4 wire or is #6 still ok?
Thanks
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Old 12-13-2010, 11:03 AM   #10
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Adding subpanel vs new larger panel


#4 would be appropriate.
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Old 12-13-2010, 11:13 AM   #11
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Adding subpanel vs new larger panel


Quote:
Originally Posted by lonric View Post
Its a square D, model QOC20MG225, series L4
If I went with a 70 amp breaker, still use #4 copper?
I am trying to research whether tandem breakers are available for you panel. Are you sure that is the panel model # and not the model # of the cover?
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