Back feeding 110v through a house. Hypothetical question only.

Factual Questions
1

******. I AM NOT DOING THIS. IT IS ONLY A THOUGHT EXPERIMENT ******

As I sit here in a dark house due to a mixup between my wife, myself and the electric company, I’m wondering what would happen if I rigged up a 110v suicide cable and hooked it up to my trolling motor and 500 watt inverter (750 peak). I used it to power my cpap machine last night and it worked fine.

My guess is that the fuse on the inverter would immediately blow as soon as my refrigerator compressor comes on. If that’s not the case, then if the AC comes on, something’s gotta give. But let’s pretend that it’s a nice fall day (it is so far) and that the AC would choose to stay off. What is the most likely outcome in this situation?

2

It would work.
That’s basically how whole-house generators work.

It’s dangerous to linemen, though, so don’t do it without proper disconnects and interlocks.

3

As B says, it would work, but (as you already figured) only until something in your house exceeds its peak or continuous current levels. It’s a bad idea. If you wanted to keep your fridge running, the usual goal, connect it directly to the inverter and hope it can handle the startup current.

ETA: And don’t ever, ever, ever backfeed your house without cutting and tagging the main line breakers. For one thing, your power source will attempt to power your whole neighborhood, and it’s dangerous to crew who think the lines might be dead and don’t check each junction carefully.

4

Most homes in the U.S. are fed through a split phase transformer (aka a single phase, center tapped transformer). The center tap is the neutral, and you get 120 volts from either line to neutral, and 240 volts from line to line. One transformer will typically feed three or four homes.

The two lines and the neutral come into your breaker box. In a typical breaker box, the connections alternate, so a 120 volt breaker just connects to one connection, and a 240 volt breaker connects to two connections and gets one connection to each line for 240 volts. Also, since they alternate, this tends to load balance the house, with roughly half of the 120 volt breakers on line 1 and the other half on line 2.

By backfeeding into one line, you are at best powering half of the house. If you don’t turn off the main breaker, you are also backfeeding the one line all the way to the transformer and out to the other homes that are fed by that transformer, and you’ll even be putting some power onto the main distribution line that will try to feed other homes in your neighborhood. As was previously mentioned, it’s also a shock hazard to any linemen out there working. Most of those wires aren’t insulated.

You’re also going to have some current that is going to go out through the line you are powering, through the transformer, and into the other line and back into your house. It won’t have enough current to power the things on the other half of your home’s breakers, and some devices might actually be harmed by such a small current level. Fan motors, for example, will just sit there and get hot since there will be enough current to heat the wires but not enough current to spin the motors.

When the AC comes back on, it’s going to be at a certain point in its AC cycle and your small generator will be at another point in its AC cycle. Since the power company’s line has much more current capability, it’s going to win and it is going to try to force your small generator almost instantly into sync. Hopefully the breaker on your inverter works, because otherwise you’re talking a whole lot of smoke.

It is much better to just run a few extension cords through your house to the devices that you want to power. Then it’s safe and you’re not backfeeding into anything. If you insist on using a suicide cord, make sure you turn off the main breaker, and it’s also a good idea to turn off all of the breakers that go to anything that you aren’t using.

5

I assume that if the power is off due to unpaid bills then the linemen came out with a big pole and hook and pulled the breaker that connects his house only. I saw this done in an old neighbourhood once - they were changing my main breaker, so turned off my power for a while.

So yes, with a 110 cheater connection you’d be powering just your house and only half. The danger comes if you are still doing this one simple trick when the linemen come back to restore the power.

(I also wonder - IANAE - how the generator device “knows” which side is ground, is there that added risk when the power is connected that what is ground could be live and vice versa? It could be as simple as a poorly constructed cheater cable…)

6

There is only one ground, and in most residential lines, ground and neutral are coupled together at many points within the system and each house.

IF it helps, think of standard 240VAC as being composed of +120 and -120, with neutral at 0 in the middle. Each half of the circuit can be used to power any standard 120VAC appliance or device. (It’s usual to try and balance the house load across both poles by distributing the breakers in the main box.)

Being AC, what’s happening isn’t quite that simple, but it gives you the idea. You have one 240VAC split-phase circuit, which can be seen as two opposing 120VAC circuits sharing a common neutral (which usually == ground).

7

Electricity works backwards. If there was a power outage to your entire city, your inverter would be trying to power the entire city!

And it is basically against electrical codes to power a house via a generator or other means without a proper generator “transfer switch”.

To learn more, search google.com for the following words…

generator transfer switch

National Electrical Code

8

You would be grounding out the neutral side to 0 volts as the neutral and ground connect in the circuit box and then to earth ground. If you flip the main breaker and it functions as intended, yes you will get power on half of your circuits and (again assuming no malfunction or human error) not back feed anything.
A 500 W inverter, With a peak of 750 may maybe start the refrigerator - if so it will be at it’s limits, and most of them will run at apx 250-300 watts after the initial draw. So it should be able to keep it running

A/C not a chance.

So yes any minor stuff you plug in to the live half of your circuits should work, exceed the limits of the inverter then the fuse or breaker will cut power. Fail to flip the main breaker and you will be backfeeding the grid, which I would think would cause a instant trip as I can see that exceeded the inverter’s limits very quickly.

You will also deplete whatever battery you are drawing from, so it is a very limited solution.