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We have installed a generator fallback, so that we can switch between using city power and generator power. The cord socket that I we have to connect the generator to the house power-grid is 4-prong and so is the cord that we have, but the new generator that we have only has a 3-prong outlet...

I have tried looking up how to rewire a 3-prong plug (male) in place of the 4-wire generator plug (male), but didn't find anything. I think the additional wire is just an extra ground...

What is the best way to go about doing this? We need to keep the 4-prong female socket on one end (because it plugs into the generator wall inlet).

Generator:
As you can see the only outlets are 120V generator outlet and a 120V RV outlet... generator with plugs in view
Generator stats:
Model 100222
AC Volts 120
AC Amps 28.3
generator stats
Home Generator Inlet:
We hooked this up to a 240V 30A breaker home generator inlet
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    The four wires are hot, hot, neutral and ground. This gives you 240 volts with two hot wires carrying 120 volts each. Some 240 volt appliances do not need neutral, only ground, 120 volt appliances need one hot and one neutral(should have ground also). Are you sure three prong on the generator is for 240 volts? Most new generators use 4 prong for 240 and 3 prong for 120.
    – crip659
    Jul 19, 2021 at 17:53
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    Please edit the question to provide the make and model of your generator, a picture of your home generator inlet and a picture and/or description of how it is connected to your house panel. Otherwise we're doing a lot of guessing. The fourth wire is probably not an extra ground, it's probably an extra power phase that supplies half the circuits in your home and helps supply 240V to all the large electrical appliances. Your generator may not have that capability. If you, or the electrician who installed this, did not understand that you may have it installed improperly.
    – jay613
    Jul 19, 2021 at 18:08
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    Edits to correct the names of some things (cord, cable, socket, plug, inlet).
    – Harper - Reinstate Monica
    Jul 19, 2021 at 18:15
  • @crip659 Okay, thank you. I was thinking of a different cord (though now that I think about it, it was probably the case for that as well...)
    – Jacob Hornbeck
    Jul 19, 2021 at 18:53
  • @jay613 We installed the generator inlet correctly, we just didn't know that the generator only had a 3-prong 120V outlet and an RV outlet (I will be adding these images to my question). Our previous generator (which we got the cord with) had the 4-prong 240V outlet. That generator stopped working, and we nor a friend couldn't fix it (mostly because we couldn't figure out what was wrong with it). We were given a new generator from an uncle who was moving. We will probably get a new generator that has a 240V outlet...
    – Jacob Hornbeck
    Jul 19, 2021 at 18:58

2 Answers 2

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Short Answer

From the comments, I am pretty sure that this can't (maybe not can't but shouldn't) be done.

Longer Answer

Even if we did rewire the cord to the 3-prong plug, it wouldn't run the 240V appliances that we would be needing to run (in case of a power outage or something). I wish I had realized this before I asked this question making me look stupid... 😒

We will probably just sell the generator (and the 3-prong plug that we got to change it to), and get a new one that has the correct outlet and is built for our needs.

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    Yes, probably best to get a better generator that's fit for purpose. I'm curious about the "240V" comment. My generator is a bit more than twice the size of the one in your picture. But it's still not big enough to power even any one of the 240V loads in my home. Well, maybe just one of them if it does nothing else. No lights, no fridge, just the dryer. :). So I don't use it for any 240V circuits. I'm curious how/why you might use it for 240V circuits?
    – jay613
    Jul 19, 2021 at 19:57
  • @jay613 Twice the size in what way? The wattage is the biggest part... though a dryer does use a lot of juice... Most of the time, we would only be using it for the well pump (so we can have water) and the blower for the furnace (only in colder weather). Sometimes we will use it to power some outlets in the house... Probably not more than that...
    – Jacob Hornbeck
    Jul 19, 2021 at 20:08
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    It also depends on type of generator. During ice storm of 98 we were lent a very small honda generator about the size of a bread box. It power our well pump no problem. We brought a 5000 amp generator after and it had problems running pump unless we used a 10 gauge cable from generator to pump control(disconnected from main panel)
    – crip659
    Jul 19, 2021 at 20:19
  • @JacobHornbeck mine's a 7500W 240V generator. It can power 120V circuits to both sides of the breaker box at 30A each. At 240V, 30A is not enough for the air conditioning, just enough for the dryer. So I don't use those. Everything else is 120V. If your well pump is 240V, and that's your only water source, you clearly need a 240V generator for that reason alone.
    – jay613
    Jul 20, 2021 at 0:53
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I would not change expensive inlets. I would not carve up expensive generator cords, unless they are already homebrew (field-assembled) and already have a replaceable socket.

I would build or buy an adapter cable that has a plug that goes into the generator, and an inline socket that accepts your existing 4-wire cable.

If you build it, you will need to learn a lot more about how split-phase AC power works, because you have tons of stuff totally wrong about that. Let me hit the high points.

Neutral is not ground.

Safety ground is a safety shield that never carries current (unless there's a fault, obviously).

Current flows in loops. Neutral is the normal way that 120V current returns. It needs to be separate from ground because Bad Things happen when they are combined.

North American power has two hots of 120V each, opposite phased.

And for a technology briefer on that, see this video.

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