Sub Feed panel

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olblue1062

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In my residence I have an existing 100 amp circuit breaker panel fed from a fused service disconnect. I am upgrading to a 200 amp service and i want to feed the existing 100 amp panel from the new 200 amp panel I will have installed.
The 100 amp panel has no MAIN breaker and is disconnected and protected by the fused service disconnect which will be replaced by the new 200 amp panel which will have a MAIN as the new service disconnect. See any reason why I cant sub-feed my old panel from a breaker in the new panel?
Thanks
HE:smile:
 
I had temporarily closed this thread, suspecting that it might be a DIY situation. After receiving a PM from its originator, I now know it is not. The OP is an electrician who specializes in a field other than residential. I am therefore reopening this thread. I offer the OP an apology for the delay and inconvenience.
 
The installation you propose is acceptable. A sub-panel does not need to have its own main breaker, so long as it is protected by a fuse or breaker from the panel (or in your existing case, the fused service disconnect) that is immediately upstream. So just put a 100 amp (or lower) breaker in your new 200 amp panel, to feed your existing 100 amp panel, and you are fine.

There is one thing that has to happen in any sub-panel, and you always must make sure this is done right. The neutrals and grounds have to be kept separate, and conductors from the neutral bar and the ground bar have to be run separately back to the main panel. But this should not be a problem for your situation. They should already be installed that way, since your existing 100 panel is downstream, and separated, from the main service disconnect.
 
The only thing to watch, after what has already been said, is the wire size. For a 100A service, you can use #4 copper or #2 aluminum for 100A, and you can also use that for a feeder that takes all the load of the house. You're adding a 200A service, so the feeder to the 100A panel is no longer carrying all the load of the house. It therefore has to be sized by 310.16 instead of 310.15(B)(6). So you need a 90A breaker if if you have the wires sized as above, or you'll need to have something larger if you want a full 100A.
 
olblue1062 said:
...the new 200 amp panel which will have a MAIN as the new service disconnect. See any reason why I cant sub-feed my old panel from a breaker in the new panel?
Thanks
HE:smile:
Click to expand...


Does the 100 amp cable have a seperate grounding conductor ??? as in 4 wire
 
suemarkp said:
The only thing to watch, after what has already been said, is the wire size. For a 100A service, you can use #4 copper or #2 aluminum for 100A, and you can also use that for a feeder that takes all the load of the house. You're adding a 200A service, so the feeder to the 100A panel is no longer carrying all the load of the house. It therefore has to be sized by 310.16 instead of 310.15(B)(6). So you need a 90A breaker if if you have the wires sized as above, or you'll need to have something larger if you want a full 100A.
Click to expand...

Depends what temperature you are going by.
 
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