OT: Home generator wiring

kolyur · Mar 8, 2011

Just bought a Yamaha inverter generator for home backup power. I want to run the necessary wiring so that any of the breakers in the main panel can be selectively energized (based on load capability of the generator of course). I'm aware that the correct way to do this is to either (1) use a transfer switch, or (2) wire the generator receptacle to a 2-pole breaker that is interlocked with the main breaker, so that they cannot be closed simultaneously. I plan to do the latter.

So far so good. The catch is that my generator is only 120v. You pay a premium for the inverter generators and I didn't want to spend $3000+ for 240v when I don't really need it. Essentially what I need to do is tie the main legs together when I'm running from generator power, so I can energize any of the single pole breakers. None of the 2-pole breakers will be used except the generator breaker (but I don't see a problem if one gets flipped, as there will be no potential difference across the legs).

The obvious solution is to just run the hot wire of the generator receptacle to one pole of the generator breaker, and put a jumper to the second pole. The breaker will be 20A and I will run 12awg to the 20A receptacle. Any thoughts on this codewise? Seems safe to me but Google is not turning up many similar installations.

Christoff84 · Mar 8, 2011

If you do this the way you have shown, you will most likely have to switch the neutral and the hot using the breaker. If you're licensed to do electrical work the guys over at mikeholt.com might be able to help you out with this, but they don't help DIYers.

The easiest way to do this and the most likely to get passed by an inspector would be to use a manual transfer switch.

leitmotif · Mar 9, 2011

kolyur said:
Just bought a Yamaha inverter generator for home backup power. I want to run the necessary wiring so that any of the breakers in the main panel can be selectively energized (based on load capability of the generator of course). I'm aware that the correct way to do this is to either (1) use a transfer switch, or (2) wire the generator receptacle to a 2-pole breaker that is interlocked with the main breaker, so that they cannot be closed simultaneously. I plan to do the latter.

So far so good. The catch is that my generator is only 120v. You pay a premium for the inverter generators and I didn't want to spend $3000+ for 240v when I don't really need it. Essentially what I need to do is tie the main legs together when I'm running from generator power, so I can energize any of the single pole breakers. None of the 2-pole breakers will be used except the generator breaker (but I don't see a problem if one gets flipped, as there will be no potential difference across the legs).

The obvious solution is to just run the hot wire of the generator receptacle to one pole of the generator breaker, and put a jumper to the second pole. The breaker will be 20A and I will run 12awg to the 20A receptacle. Any thoughts on this codewise? Seems safe to me but Google is not turning up many similar installations.

Right from the start this seems to break the rule
"Do it right the first time and be done"
OR if you cannot afford or take the time to do it right --where are you going to find the time to rip out mistakes and spend what you should have in the first place.

I would go with the transfer switch as recommended. I have no idea of how you are going to interlock the main switch with a breaker for the generator -this is going to be hard to find.

Also you should NOT use plugs and cords - good way to end up with a hot plug hanging out there and zapping the wife.

Sooner or later with your setup you will overload the generator.

Dan Bentler

kolyur · Mar 9, 2011

I have no idea of how you are going to interlock the main switch with a breaker for the generator -this is going to be hard to find.

The interlock is quite common around here and does pass inspection (see pic). Square D even makes one for their panels. I guess I assumed they are acceptable everywhere--perhaps this is not the case.

Also you should NOT use plugs and cords - good way to end up with a hot plug hanging out there and zapping the wife.

The receptacle on the generator circuit is a male inlet, which will only be energized when the main is off and the generator is connected. This eliminates the need for any unsafe male-to-male cords.

Sooner or later with your setup you will overload the generator.

Isn't this a possibility with any generator setup?

MikeW · Mar 9, 2011

... Essentially what I need to do is tie the main legs together when I'm running from generator power, so I can energize any of the single pole breakers. None of the 2-pole breakers will be used except the generator breaker (but I don't see a problem if one gets flipped, as there will be no potential difference across the legs). ...

So all the loads that will be powered by the generator are already on the same phase in the breaker panel? You are going to manually shut off all the loads on that same phase that you don't want powered when the generator is running?

I would draw up clear schematics/ plans and run it by at least an old electrician (i.e. There are old electricians and careless electricians but there are no old, careless electricians.) or preferable the appropriate inspector if your locale requires one. Doing it "not quite up to code" will be a hard sell to the insurance agent if something bad happens and you need to collect on a policy, especially if it's a life policy, heaven forbid.

Also check the time-current protection curves on the generator to see exactly when the breakers trip to make sure what the "20 amp breaker" is really good for for extended periods of load and then the a larger load (i.e. refrigerator) starts up.

Is it a long distance between the generator and the breaker panel/ voltage drop an issue using #12?

mvaughan · Mar 9, 2011

I never had a problem finding, inspector approved, breaker interlocks for generators(most electrical supply houses sell them). As long as your generator is providing over current protection for the #12 wire, I don't see a problem with the install. I would also probably just make my original installation code compliant.....If anyone is like me and takes short cuts on the install, it might be years before it is installed right, if ever. If your going to use all approved parts you might as well get it inspected, at least here the home owner can pull his own electrical permits. If you do that generally the inspector will help answer any questions you have.

Good Luck!

hanziou · Mar 9, 2011

@kolyur
What you say make sense to me. Thanks for the picture of the interlock plate.

So all the loads that will be powered by the generator are already on the same phase in the breaker panel? You are going to manually shut off all the loads on that same phase that you don't want powered when the generator is running?

Based on the OP's description and photos, there are two separate (120V) phases in the panel. He will be drive both those phases with the one hot from the generator. ("hot wire ... to one pole of the generator breaker, and put a jumper to the second pole") He also states that he will select which breakers to energize.

As far as loads go, heaters seem to be the big ones. I found my refrigerator runs ~1.5A (3A with the doors open (lights)). The biggest 120VAC loads I found were the toaster oven and bathroom heaters @ ~13A each.

Paul T · Mar 9, 2011

kolyur said:
Just bought a Yamaha inverter generator for home backup power. I want to run the necessary wiring so that any of the breakers in the main panel can be selectively energized (based on load capability of the generator of course). I'm aware that the correct way to do this is to either (1) use a transfer switch, or (2) wire the generator receptacle to a 2-pole breaker that is interlocked with the main breaker, so that they cannot be closed simultaneously. I plan to do the latter.

So far so good. The catch is that my generator is only 120v. You pay a premium for the inverter generators and I didn't want to spend $3000+ for 240v when I don't really need it. Essentially what I need to do is tie the main legs together when I'm running from generator power, so I can energize any of the single pole breakers. None of the 2-pole breakers will be used except the generator breaker (but I don't see a problem if one gets flipped, as there will be no potential difference across the legs).

The obvious solution is to just run the hot wire of the generator receptacle to one pole of the generator breaker, and put a jumper to the second pole. The breaker will be 20A and I will run 12awg to the 20A receptacle. Any thoughts on this codewise? Seems safe to me but Google is not turning up many similar installations.

I don't think anything short of a transfer switch is going to meet code. I've never seen a transfer switch to send 120 1PH to 240 1PH, but as you said you'd simply wire both hot legs of the switch to the single hot leg from your generator.

Aside from that, what you said should work fine from an electrical standpoint. Just be careful out there!

Paul T

leitmotif · Mar 9, 2011

Let me explain a little guys.
FIRST I am an old electrician. I make my living as industrial electrician but do a fair amount of home stuff. I have done a lot of repairs (ripouts) to do it yourself installations. I do NOT wire to meet code but wire to meet rule of no fire, electrocution and NO call backs.

The insurance company is another consideration.

Kolyur Thanks for the interlock suggestion. Did not even consider that but again I do not use these simple things because they are so simple for homeowner to remove. IF I were to use it I would weld it in. IN my experience if you use cord and cap someone will get it wrong. Even recessed that male connector is the first thing I would at minimum remove.

I heartily recommend doing it right install a transfer switch and second panel to carry loads you want run off generator. One advantage is you wont worry while at work. Wire Xfr switch with 240 off panel to second panel and either do not install breakers on undesired leg or do not hook up the other leg - just tape it good for future use. That way everything is ready to go when you get the correct size and voltage gen set. If you insist on using cap and plug use incompatible configuration ie twist lok OR ??

Dan Bentler

kolyur · Mar 9, 2011

leitmotif said:
Kolyur Thanks for the interlock suggestion. Did not even consider that but again I do not use these simple things because they are so simple for homeowner to remove. IF I were to use it I would weld it in.

That's the biggest drawback of these interlocks--they rely solely on the panel cover being in place. There is one brand (Cutler Hammer I think) where you have to buy a replacement cover with an integrated interlock, rather than a retrofit kit, but that still doesn't prevent the homeowner from just removing the cover to bypass it.

rguimond · Mar 9, 2011

You really have to be wary if there any "split" receptacles. These are generally wired with #14/3 wire (2 hots and 1 neutral). Since they're wired to hots in opposing phase, there can never be more than 15A on the Neutral. If there is an equal draw from each hot, there is no current through the neutral. if you re-configure the panel so that both hots have the same potential, it's possible that a #14 neutral could be asked to carry up to 30A if it's connected to a split receptacle.

leitmotif · Mar 9, 2011

rguimond said:
You really have to be wary if there any "split" receptacles. These are generally wired with #14/3 wire (2 hots and 1 neutral). Since they're wired to hots in opposing phase, there can never be more than 15A on the Neutral. If there is an equal draw from each hot, there is no current through the neutral. if you re-configure the panel so that both hots have the same potential, it's possible that a #14 neutral could be asked to carry up to 30A if it's connected to a split receptacle.

Excellant point. Completely forgot about em. Seemed most common in kitchens. Don't like em.

Dan Bentler

OT: Home generator wiring

kolyur

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