Now I'm no certified electrician, but I'm not a novice either. I'd say semi-pro. Anyways, I bought a house that was built in the 70's and it's got something in the panel I haven't seen before. I have one 240v breaker labeled "gen lighting" which, sure enough, powers multiple lights and 120v outlets throughout the house.

In theory, in the event a power outage, if one were to backfeed the panel using a 120v generator hooked up to a 120v circuit on the same side of the panel, would flipping on the double pole 120v breaker essentially energize the entire panel? Not for running any 240v circuits of course, but just for the purposes of powering 120v circuits on the other side of the panel?

 

Backfeeding a panel is very dangerous and not approved anywhere in the U.S. or Canada so the rest of your question is moot. What you have is NOT 240v lighting. it is a multiwire 120 volt circuit.

 

Although I agree with what Ray has said, I am trying to figure out what you have. Is it possible you have a splt bus panel with a 240 volt 2 pole lighting main? Can you provide a picture of the panel?

 

The OP might also have a split bus panel.

 

With a 120 volt generator hooked up in any fashion to one side of a 240 volt panel ...

If there are no 240 volt loads on the "general lighting" 240 volt double breaker's circuit then flipping it on will not energize "the other side" of the panel.

But flipping on a 240 volt breaker with 240 loads still switched on will energize "the other side" of the panel for electrocution hazard purposes but not for the purposes of using loads "on the other side". You are going to get a backfeeding of a different flavor, from the "live side" of the panel through the air compressor or water heater or any European 240 volt lights etc. to the "dead side" of the panel. The voltage measured there will depend on the 120 volt loads "over there" that are switched on and the resistance of any 240 volt loads on the affected 240 volt circuit that are switched on.

 

Welcome to the forums!

Since residential electrical services are 120/240V services, they are not designed to accept, and operate safely with, only 120V hot-to-neutral power coming in.

If you're not going to install a 120/240V backup supply, the safest method for you to use would be to install a separate transfer panel that opens its connection to the utility feed when switched, re-work it to take a 120V supply, and move the loads you want to back up to it.

 

Thanks for the ideas guys. Like I said I haven't come across this before and I don't know much about multi-wire 120 circuits.





So if I have 120v feeding that leg, and flip this multi wire circuit on, it won't do anything for the opposite side of the panel but it also won't create any additional hazards right?

 

Provided that all you have on this multiwire branch circuit (MWBC) are 120 volt receptacles and (120 volt) lights, bathroom fan, etc. with or without wall switches, then flipping on the (double) breaker for that circuit will not create any safety hazard on the other leg of your panel. It would be no different from flipping on a (single) breaker for a non-MWBC branch circuit on the leg of your panel not powered by your generator.

The most common kind of MWBC found in the home is like this 240 volt lighting circuit you have. Two hot wires, usually one is red, have 240 volts across them and they share (one) neutral for 120 volts hot to neutral. Downstream you can add non-MWBC (120 volt) sub-branches to the MWBC, tapping off one hot and the neutral. It is not necessary to use red wire for these non-MWBC branches; common black and white conductor Romex is commonly used here too.

Your panel as shown is not a split bus panel. A split bus panel has all the (double) 240 volt breakers near the top and all the single breakers at the bottom and also one of the double breakers is a "submaster" for the entire collection of single breakers down below.

In case you did not already notice, the A side and the B side of the 120/240 volt line do not correspond to left and right absolutely. For your panel the top black box (main breaker) has the middle and right fat wires are the A and B hot wires entering the very top and you can think "left" and "right" for that portion of the panel contents. But down below the A side and B side branch circuit breakers alternate left and right, for example all the odd rows have the A side breaker on the left and all the even rows have the B side breaker on the left. This is needed so a double breaker can fit on both an A leg fin and a B leg fin behind.

 

AllanJ is right, that is not a split bus panel. What you have is an older aluminum bus GE main breaker panel with either a 200 or 225 amp main breaker. You cannot feed this panel with 120 volts from a generator and there are no interlock covers to fit it. You would need a transfer switch/panel or transfer switch and separate panel if you want to use a 120 volt generator to power multiple selected circuits transferred to the generator panel.