Generators - Backfeeding - 120V

[quicksandfarmer]

I just need to know if I can power both legs of 120V to get 120V at outlets and light fixtures.

You can, but it is a dangerous thing to do. It is very common for both legs to share a neutral. This only works because normally the two legs are out of phase and don't both draw at the same time. If you connected both legs to the same source they would be in phase, and the neutral would be handling current from both. The neutral would be overloaded without either circuit breaker tripping, and it could easily overhead and start a fire.

A much better solution is to move all of your essential circuits onto the same leg.

 

[TRR]

All you need is a jumper between the 2 legs. It can be done in the panel box by replacing the 220 breaker with a jumper as previously mentioned. Or by using a suicide cord and plug it into an outlet on one leg and another outlet on the other leg. Or any other way to connect the two together. I really hate to mention this because it is dangerous if you ever make a mistake, but here goes. Some panels have threaded holes in the bus bars for lugs. A wire can be attached to each leg and run to a switch outside the panel. Flipping the switch to "on" will directly connect the two legs. If it is ever turned on when power is coming from the power company, I will guarentee you will have an electrical fire!

Personally, I would move the circuits to one leg or put in another smaller panel and put all the stuff to be powered by the generator in there and use a transfer switch between the 2 panels to select between generator and line power.

 

[JB4310]

People aren't reading my posts correctly.

1) I know its not legal. Nor is speeding, rolling stop signs and having a few too many beers and driving that people do. Hence why I'm not discussing the legality of it.

2) I am a commercial pilot. Very well and used to doing things the same way the 100,000,000th time over and safely too. I'm not an idiot and can get past the world's reasons to design for the lowest common denominator.

3) I do NOT need 220V.

Now, I may be able to swap around some breakers to try and move some to the powered leg but this still might not work as I have NO room for expansion in the CB panel. Hence why I can't put in another line, breaker....blah...blah, etc.

I just need to know if I can power both legs of 120V to get 120V at outlets and light fixtures.

I'm not the safety police, just trying to get you to do what you want safely. Not criticising or judging. I gave you my answer that yes you could do it, but gave you the one example of a problem that could possibly result with shared neutral circuits (probably wouldn't be a problem for just lighting loads).

Pull the plug to a high amperage 220v outlet, like to the dryer or range. Make a jumper plug to put a short across the powered lugs that are normally 220v.

Or, at a high amperage 220v breaker, remove the circuit wires and place a jumper wire across the terminals to feed the other leg. Size the jumper wire accordingly.

Interesting and would work super easy, but that's getting even more Frankensteinish, more to remember to undo after.

Though it may be better than 2 male/male cords going to different rooms in the house to power both sides of the panel. Got me also thinking of some kind of custom cord to feed thru that 220 outlet, so he could hit both sides thru one source. Basically a jumper with the male 220 on one end and 2 male 110's on the other. I know that's a Frankenstein setup as well :confused2:

JB

 

[Canada_CT230]

I don't want to do any conveluted wiring (in the dark). I want a simple 1-2-3 system.

I think I will try to move a few circuits to the live side and be done with it for now.

 

[JB4310]

You can, but it is a dangerous thing to do. It is very common for both legs to share a neutral. This only works because normally the two legs are out of phase and don't both draw at the same time. If you connected both legs to the same source they would be in phase, and the neutral would be handling current from both. The neutral would be overloaded without either circuit breaker tripping, and it could easily overhead and start a fire.

A much better solution is to move all of your essential circuits onto the same leg.

Oh, very good point, I already warned him of the shared neutral issue, as I recognised that as a potential problem with the neutral being overloaded, But I didn't even think about the fact that the breakers would not be overloaded, and would not trip, possibly causing a fire.

Not all houses have those shared circuits but my house does have several.

If he did have them he would really have to be careful not to exceed 50% load on those circuits.

JB

 

[tsteahr]

All this discussion about frying the neutral, starting a fire, blowing up a panel, etc is true in theory. But lets remember the OP has a 3000W 120v generator. He has 25 amps or less available. Regardless if this 25 amps is split over one hot leg or two, the neutral will still only see a max of 25 amps. This is not going fry anything.

Just trying to keep some perspective here...

 

[radioman]

Its just easier to have a manual transfer switch panel. Super easy to install yourself. you just pick the circuits you want and pull out of old breakers and connect to new panel that is the transfer switch. No need to worry about 220, no need to worry about backfeed, no need to worry about shutting down gen when power comes back on and you will know its back on from circuit you havent transferred over.

I realize it sounds complicated from my statement, but trust me, its super easy. for 300 bucks or less like this one Shop Reliance 7500-Watt Transfer Switch Kit at Lowes.com .

I installed one after one time power went out and I BF in house with main breaker off and I realized I had no way of knowing when power is back on unless i shut down and switch main back on. So I went out and bought a transfer switch. its worth every penny since I can only power which circuit I wanted ahead of time and still know when power is back on without worry about backfeeding to one lug only or remember to shut off main.

 

[JB4310]

All this discussion about frying the neutral, starting a fire, blowing up a panel, etc is true in theory. But lets remember the OP has a 3000W 120v generator. He has 25 amps or less available. Regardless if this 25 amps is split over one hot leg or two, the neutral will still only see a max of 25 amps. This is not going fry anything.

Just trying to keep some perspective here...

Could get a little warm if it was all going thru a 15 amp 14 ga shared circuit.

But I agree, that would not be very likely, that his entire draw would be thru 2 circuits.

JB

 

[aczlan]

Though it may be better than 2 male/male cords going to different rooms in the house to power both sides of the panel. Got me also thinking of some kind of custom cord to feed thru that 220 outlet, so he could hit both sides thru one source. Basically a jumper with the male 220 on one end and 2 male 110's on the other. I know that's a Frankenstein setup as well :confused2:

If you insist on doing this, the safest way is probbaly to get a 20 amp 220v breaker. Wire in your 20 amp outlet into one side of the breaker with 12 gauge wire and run a jumper from that side of the breaker to the other using at least 10 gauge wire.
Then when that breaker is on, you will feed both sides of the bus, but if you forget to turn it off, the wire will hopefully hold up to the current long enough to trip the breaker. I would recommend that at very least, you get one of those sliding interlocks so that it is physically impossible to backfeed the line to the road.

If you need to free up some spaces to make this work, there are double mini breakers available for most panels that will let you relocate two circuits to make space for your frankenstine setup

Here is a basic wiring diagram:

Please note that I do NOT recommend powering both legs of your breaker box with 120v in this fashion, but if you must do that, this is probbaly the safest way to do it.

Aaron Z

 

[crazyal]

It's very easy to do. Do you have a 220 outlet you can plug your generator into (yes I know you don't want 220, just follow me). If you connect up both 'hot' wires together and then to your 'hot 110 leg from your generator you'll power both sides. If you really want to do this I would put a fuse or circuit breaker in the middle of the jumper between the two hot legs.

If you don't have a 220 outlet you can make a second cord and use the second outlet on the generator. Just find two different outlets that are on different legs.

I'm not the safety police so I'm not going to tell you if you should or shouldn't connect a generator up to your house wiring without using a transfer switch. However if you did add in a transfer switch you could wire the same way and get 110 to both legs. Also with a transfer switch you wouldn't need to worry about the one in a million chance of someone turning on the main breaker with the cord and jumper or the two cords connected up (even with the generator off it'll still short both legs together).