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Tornado took out power around here for a good while. Parents aren't here and I'm stuck with the task of hooking up a generator. I'm not savvy with this stuff very much at all.

Here's the issue. The connection coming out of the house is L14-30P. The generator has L14-30R. In my head we just need a 30a cable between the two.

The only stuff we have right now is an adapter L14-30P to L14-20R. My dad says this adapter is needed because it puts the voltage down to 120v. It's literally just an adapter. He says at 240v it would fry our equipment and appliances in the house. Doesn't make sense to me to have this adapter, then have a L14-20P to L14-30R cord connected between the adapter and the house. Seems like an extra useless step right?

I'm not worried about breaker positioning and all that. I just need to make sure I have the cords done properly between the generator and the house. I've got the rest done.

Feel free to correct everything that is incorrect about what I just stated, logic and all.

Here is the front of the generator :

enter image description here https://imgur.com/a/4SzrEbm https://imgur.com/a/Emj9TKR

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  • Can you take a photo of the outlet/inlet to the house? If you look at the electrical panel, is there a smaller panel off to the side with a 'whip' (metal) going to the main panel, and perhaps some different looking fuses? Maybe take a photo of both? – J.Hirsch Apr 14 '20 at 19:41
  • Your title is misleading... your house (at least most in the US) receive 240v from the electric utility and split that into two 120v phases. Each phase supplies roughly half of your circuits. Your generator is setup to provide a lesser analog of that. Before bringing it online, you should shut off anything non-essential, and engage your interlock that prevents utility power from coming in. Then you can provide the 240v via the wired connection. Don't turn on more than it can handle. – DaveM Apr 14 '20 at 20:56
  • Cross posted here: electronics.stackexchange.com/q/493103/152903 – Solar Mike Apr 14 '20 at 22:48
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To answer your specific question, the difference between L14-20 and L14-30 is maximum amperage, not voltage. Both carry both 120 volts and 240 volts (actually two legs of 120 which can be combined for 240).

As you suspected, the combination of the adapter and cord are useless (as opposed to a direct L14-30 to L14-30 cable). Actually, it’s worse that that. The L14-20 connectors are only rated for 20 amps. Since the generator can produce 30 amps, those connectors could melt or catch fire!

I’m assuming your father went shopping for a 30 amp cable and the sales critter sold his those, what it had, making up the story about voltages.

For safety, you really need an L14-30P to L14-30R cable. Since you don’t have one, I suggest you follow @JACK’s advice and plug the appliances you need directly into the generator instead.

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  • This is exactly as I suspected. Thank you. I will add more pictures in a little bit to confirm – DerekA Apr 14 '20 at 17:43
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Do yourself a favor and just run some extension chords from the 120 V outlets on the generator into your house and plug the appliances you need into them. If you are not familiar with the setup don't mess with it. I'm not sure what adapters you have but most adapters are bad news...

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    I was thinking that too, Jack. But if the generator inlet was properly installed on the house and he has a proper interlock on the panel, it should be safe just to run out and buy a cable with the correct ends. It would be helpful if the OP posted a picture of the generator transfer switching or interlocks for us to be more helpful. – George Anderson Apr 14 '20 at 17:24
  • I had to step out and don't have a picture of it but I can confirm there is a proper interlock on the panel. Here's the inlet though m.imgur.com/a/8ceieuX – DerekA Apr 14 '20 at 17:34
  • @GeorgeAnderson true, but what scared me was the OP's comment about the adapter "putting the voltage down to 120V".. Has it been modified? – JACK Apr 14 '20 at 17:34
  • The adapter hasn't been modified. What I'm saying is that I believe my father is incorrect in stating that the adapter downvolts to 120v. It doesn't do that at all. It's a standard L14-30P male to L14-20R female adapter. – DerekA Apr 14 '20 at 17:36
  • Let's wait until the OP can post a pic of the transfer/lockout. ...BTW doing OK out here. nice weather here the the great NW. – George Anderson Apr 14 '20 at 17:38
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I'm trusting you on having a proper interlock.

Get help

The deal-killer is the father saying "because it puts the voltage down to 120v". Whoa, whoa, whoa, what the heck is going on there!!??

That place serious doubt as to the configuration of the whole setup. Why does it need 120V? How did dad wire this thing? Is this being done in the adapter cables or the panel wiring?

These are questions only Dad can answer, and you'd either need to listen to his advice, or else start popping covers off things and shooting us photos.

If the wiring from the inlet to the panel is tip top, then you could just go down to the RV supply and get a 30A L14-30 extension cord, and Bob's your uncle. But we'd need to know that.

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  • That's why I wanted photos of the inlet. There should be 240v line split out to 2x 120v (Different phases) but that's done at the disconnect inside. I have seen cord splitters, but that puts out 2x 110v... shared neutral... so yeah this seems a hack that could kill someone. – J.Hirsch Apr 15 '20 at 18:18
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FIRST: DISCONNECT THE MAIN BREAKER!

I realize that you may end up running extension cords, but if for any reason you are going to go through the panel, please turn off the main breaker to the house.

You do NOT want to kill a lineman by energizing that.

Please do this.

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