Splicing sub panel feed

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zcanyonboltz

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I am doing a service change where an all in one panel has an ac in it then feeds a sub panel with SER in house with the rest of breakers. I am aware since the whole house is not fed from the sub panel feed because of AC in main I must use a breaker that is rated to same or less than the SER. Can i splice the SER in panel to go from 2/0 aluminum to #1 copper since 2/0 wont fit under a 125 amp breaker? Something is making me wonder if its legal to splice the sub feed? # 1 copper is rated to 130 amps and 2/0 aluminum to 135 so I know my wire sizes are rated to at least 125 amps. Thanks
 
Yes you can splice but do you need to? I know 125 amp Square D HOM, Eaton BR and Siemens Q are listed for up to 2/0. Are you installing the SER new? If so why not use 1/0? Unless you calculated load is over 120 amps 1/0 is fine with 125 amp over current protection.
 
zcanyonboltz said:
I am doing a service change where an all in one panel has an ac in it then feeds a sub panel with SER in house with the rest of breakers. I am aware since the whole house is not fed from the sub panel feed because of AC in main I must use a breaker that is rated to same or less than the SER. Can i splice the SER in panel to go from 2/0 aluminum to #1 copper since 2/0 wont fit under a 125 amp breaker? Something is making me wonder if its legal to splice the sub feed? # 1 copper is rated to 130 amps and 2/0 aluminum to 135 so I know my wire sizes are rated to at least 125 amps. Thanks
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You are misunderstanding 310.12. Your feeder conductors are allowed to be sized using 310.12 even if you have some of your load at the meter/main because the feeder conductors are never required to be larger than the service conductors. See 310.12(C).
For example if you have a 150 amp meter/main with spaces for breakers and feed through lugs you can use 2/0 AL for the service conductors and the feeder even if you have loads fed from breakers on the bus in the meter/main.
 
After rereading the OP I get the sense that maybe you are putting a 125 amp branch breaker in a main panel that is larger than 125 amp. If that is the case, then you are correct that you can not use 310.12 allowances. For example if you have a 200 amp main panel with a 125 amp branch breaker you will need conductors for that feeder to be sized per Table 310.16.
My comments in my previous post were assuming that you had a feed through meter main.
 
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