Electrical – Replace Circuit Breaker on Split Bus Panel

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I want to add a 50 amp 220V circuit breaker to my split bus panel to supply a welder. I have two options. One option is to use the empty slot (blue arrow) or replace the spare 220v breaker that is currently not doing anything (red arrow). If I understand correctly, both options will keep me in compliance with the 6 throw rule. The "problem" is that both option are above the split (dashed green line) and are always hot because I don't have a main disconnect. My questions are (1) how do I replace these circuit breakers safely and which option would be better (red arrow or blue arrow). Thanks.
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Best Answer

6 of one, half dozen of the other on the red or blue arrow issue. You can plug a breaker in hot (assuming you know the proper safety precautions). I would probably swap out the unused one, just because the panel cover would not need to be altered (I'm lazy).

If you are uncomfortable working on live equipment, you can ask the utility to disconnect you (pull the meter). Generally that means they come out and do it one day, then come back and put it back in the next day. SOMETIMES you get lucky and they do it faster, but you can't count on it, so be prepared to have no power for a day. If you have one of the new "Smart Meters", they often have a remote disconnect capability so the utility simply sends it a signal to disconnect or reconnect, so it can be just minutes.