But are houses anywhere wired with a shared neutral back to the breaker box?

Not in a long time it's not to code to do so and if they did all your breakers should be double pole breakers
years ago you would share neutral in commercial buildings.
and use like this

And it's a little hard to overload a neutral A short is about the only way I seen it ever happen
You'd more then likely over load the branch with a AC, hotwater heater or stove
By using the single branch to feed both sides of the panel, But lights and tv or computer would care less.
Oh and I forgot one as crutschow said Dryer

 

Hmm... I'll have to open up the breaker panel and check. I was expecting shared neutrals in the walls as it's still allowed by Florida code as of 2017 (section E3701.5 here).

 

Remeber if both L1 and L2 are carrying a current and sharing a neutral, the current in the neutral is the difference Not the Sum!
Max.

... and since both phases are off by 180*, assuming they're both drawing the same power, would current at the neutral be zero?

 

Where it used to occur was some time ago in N.A. the regulation was for kitchen duplex outlets to be wire with L1 say, top outlet, L2 on the bottom, both with a shared neutral.
In this case, with a 10A appliance plugged into the top and another 10A in the bottom, the neutral current = zero.
Now not allowed.
Max.

 

Where it used to occur was some time ago in N.A. the regulation was for kitchen duplex outlets to be wire with L1 say top outlet, L2 on the bottom, both with a shared neutral.
In this case, with a 10A appliance plugged into the top and another 10A in the bottom, the neutral current = zero.
Now not allowed.
Max.

Interesting ... but is it allowed to split a house between the two phases? Say, L1 for the north side and L2 for the south?

 

You could I guess, as long as they had individual neutrals, but not considered good wiring practice.
BTW it is single phase, but split.
Max.

 

A split-phase or single-phase three-wire system is a type of single-phase electric power distribution

 

You could I guess, as long as they had individual neutrals, but not considered good wiring practice.
BTW it is single phase, but split.
Max.

A split-phase or single-phase three-wire system is a type of single-phase electric power distribution

Right... and I agree, it's important to make a clear distinction between split-phase and separate phases, such as the three-phase standard system.

Thanks for clarifying

 

Before you tie the "neutral" wire from the generator to the frame ground be sure to check the voltage between them with the generator running. I have heard a report that on one model of one brand the center of the 120 volts was somehow tied to the frame and so the body of the generator package was sort of hot.

And since the generator package is an isolated power source until you attach a ground some place, there is no safety hazard of shocks to ground until you tie it into a grounded system. Of course, most house wiring is neutral grounded and so once connected grounding rules do apply.

I'm currently using a generator that supplies 120V split phase (240V with center neutral) to power my entire house after storms, and it works great. However I would like to have the option of using my smaller 120V-only inverter generator instead because it's much better on fuel, however I need 120V split phase to safely power both branches of the house. Are there any safety concerns with creating split phase 120V using a transformer as shown below assuming the transformer is of adequate size? The center tap would be tied to earth through the home breaker panel. It looks good to me but I just wanted to run it by the crowd in case I'm missing a safety concern.

Also does anyone know off hand of a transformer with this configuration that is capable of sustained 3kW minimum?


View attachment 185368

Hevi-Duty brand industrial control transformers are rated at the wattage that they can carry constantly with a minimal temperature rise. If the rating is 3KVA, then after a week delivering 3KVA it will be warm but you can hold your hand on it. But they are big and heavy and not the cheapest you can find. But they are approved for production equipment by the two auto companies that I have built machines for, and I never had one fail.

 

Everyone calls it single phase which it is and it isn't. Around 9KV is delivered to the primary as single phase. The house gets 240 SPLIT phase, a 240 V center-tapped transformer where the center tap is neutral. There is only one point where neutral and earth connect on the secondary.

 

Given the generator is rated 2800 watts continuous and 3500 watts surge for 10 seconds, with no VA rating, what size transformer in VA would you guys opt for? I have no idea what the average house power factor is. Am I wrong in thinking that a load with a tiny power factor would start looking like a short to a circuit breaker? Meaning that maybe a 3.x kVA transformer would be fine since the generator circuit breaker should trip if the current gets too high, regardless of actual watts dissipated by the load.

 

I see no reason to go over 3.5kva .
Max.

 

Meaning that maybe a 3.x kVA transformer would be fine since the generator circuit breaker should trip if the current gets too high, regardless of actual watts dissipated by the load.

I would think that 3-3.5kVa should be more than adequate (if you find you really need a transformer).
I believe transformers that size are not cheap.

 

I would think that 3-3.5kVa should be more than adequate (if you find you really need a transformer).
I believe transformers that size are not cheap.

No, at least not for good new ones. They are not cheap, although the good ones that last forever are free from any additional costs for repairs or replacements. It could be slightly more efficient to use a smaller transformer to feed the opposite phase side, and feed the side with the greater load directly. So you would need to determine which side that was. And it may also be possible to arrange your loads so that you only had to supply power to one side of the panel. That may be an option worth considering. It may also be an invalid suggestion, given that I have not seen your installation.

 

My go to for transformers is Hammond, I have also picked up the odd one from local electrical suppliers.
Max.

 

Thanks again everyone for the info. When I get a few minutes I'll go pull the cover on the breaker panel and try to determine if I really need a transformer (if the walls are wired with shared neutral) and then play it from there.

 

Thanks again everyone for the info. When I get a few minutes I'll go pull the cover on the breaker panel and try to determine if I really need a transformer (if the walls are wired with shared neutral) and then play it from there.

You should also consider which electrical things you would choose to use while running on a generator. When our power fails things do change a bit.

 

When I get a few minutes I'll go pull the cover on the breaker panel and try to determine if I really need a transformer (if the walls are wired with shared neutral) and then play it from there.

We're waiting with bated breath for the answer.

 

We're waiting with bated breath for the answer.

I am not eagerly waiting, I am wondering about the actual use of power that would be happening during a power outage. In my area a power outage leads to a big shift in activities.
In addition, most folks do not use most of the power that could be provided by by their household wiring. Consider that probably most 15 amp outlets do not even have loads plugged in to them, and those that do have a load probably do not have a 15 amp load. So shared neutrals may not really be an issue at all. You can use a clamp-on ammeter to see just how much current is actually flowing in each neutral line, and then know for sure.

 

To be honest, I don't see a 2800 watt generator as enough. Other than to keep a fridge alive during a power outage, a computer and a few lights. I wouldn't use it for running an AC, nor an entertainment center, and definitely not for heating. But yes, powering a pump to get water out of the basement can be a priceless resource in an emergency.