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I have a floating neutral inverter generator (low THD - Firman model WH02942) with a TT-30R female receptacle that I'd like to connect to a L14-50 male inlet on our house (GE model T050N). I was looking for a cable which would make this possible but haven't had much lock so am wondering if there's an underlying issue with what I'm trying to do. Of course exceeding the amperage rating of the generator will cause its built in breaker to trip, but I'm wondering if there's anything aside from that or any considerations here.

As a side note, this setup will include the interlock made by the company that made the service panel to make any backfeeding to the mains impossible.

EDIT 11/11: Here's a picture of the inlet label and its breaker on the service panel:

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  • What in your house are you trying to run on your generator?
    – ThreePhaseEel
    Commented Nov 11, 2021 at 4:07
  • @ThreePhaseEel It'd be limited to things which don't have a major draw (i.e. no central AC, no electric oven) - maybe things like refrigerator, pool pump (though that's not a trivial draw but perhaps on low variable speed), gas tankless water heaters, low-wattage pipe warmer, perhaps microwave in lower power mode. Not trying for comfort, but getting through an outage, especially winter storm related.
    – g491
    Commented Nov 11, 2021 at 4:29
  • Can you localize all those things to a handful of circuits?
    – ThreePhaseEel
    Commented Nov 11, 2021 at 4:32
  • @ThreePhaseEel I'd expect I could get what I'd want to run down to a half dozen or so circuits
    – g491
    Commented Nov 11, 2021 at 13:32

2 Answers 2

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You can build a "half" adapter cable

Cordage is special cable specifically made for flexible cords for AC mains power. Anything with a "cord and plug" uses it. Toaster, desktop PC, iron, plug-in washing machine, refrigerator, you name it.

Cordage uses the same amps as wall wiring (actually a bit higher sometimes) except when it is specified, the ground wire is counted. /3 means black white green. /4 adds red.

It is legit to make your own cord.

You would need 10/3 cable at the least, which is expensive, but using 10/4 might be wise so you don't have to buy the cord again if you ever upgrade generators.

On one end, you need a TT30 plug. On the other end, an L14-50 socket.

Ground to ground.

Neutral to neutral.

Hot to one of the hots. Pick one.

You must run this with all 240V breakers switched off, including the ones you do not realize are 240V breakers :) Otherwise really weird stuff will happen. Wouldn't start a fire, but might damage motor appliances.

You will find half your 120V circuits work and half do not. If that is satisfactory to you, that is fine. If you'd rather the other half be powered, then change your adapter cable to connect to the other hot instead.

Why not split hot to power both sides? Problem. Some houses have shared-neutral or multi-wire branch circuits (MWBC). This only works because the hots are on opposite phases. If they were on the same phase, neutral would be overloaded. If you can review your panel and prove your house is MWBC-free, then you should open up the inlet and join the hots at the inlet wiring... not in the adapter cable, because it might be used on somebody else's house!

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(Looks up the odd thing that is a TT-30, mostly seen in RVs, evidently) You have a 120V 30A output trying to feed a 240V 50A inlet. You're not going to find a pre-built cord for that.

You can build one IF you throughly understand what you can't run (any 240V circuits, and half of your 120V circuits - obviously number of circuits at once more limited by current drawn.)

The amperage is no big deal if you limit your use (the inlet wiring can safely handle more than your generator can feed it. If you overload, the generator breaker will trip and let you know you asked too much of it.)

There is a way you can make power available to all your 120V circuits, but if you have any Multi Wire Branch Circuits you cannot take the easy approach to that. The non-easy way is either sell the 120V generator and get a 120/240V generator, or add a 120V/240V autotransformer to the 120V generator output.

If and only if you have no MWBCs, you can build your cord so that generator hot is connected to both hots on the 50A end. However, if your cord is ever used anywhere else that does have MWBCs, it could cause a hazardous condition.

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  • Is there a way to know for sure if the inlet is 240V? I ask because the label on it and on its breaker both say 120/240V (added images to the question just now). Are there certain brands of autotransformer I should look for if buying one?
    – g491
    Commented Nov 11, 2021 at 15:52
  • It's a 120V/240V (locking 240V with neutral and ground - L14-50 defined) inlet. The dual breaker on a US system means it's 240V - having neutral makes it 120/240V. Product recommendations are off-topic, but you'll probably find selling/buying generator more cost-effective than buying a suitable autotransformer.
    – Ecnerwal
    Commented Nov 11, 2021 at 16:06
  • Could I have an electrician put a different inlet and/or breaker in and then be able to use the generator as is? Sorry if this is a dumb question - I don't know much about electrical. Thanks
    – g491
    Commented Nov 11, 2021 at 16:53
  • (the reason for not wanting to get a different generator if possible is because to get low THD, propane, and floating neutral, the next level up is quite expensive >$1k)
    – g491
    Commented Nov 11, 2021 at 17:00
  • If you (or your electrician) locate all of your 120V loads (that you want to power with this) on one "leg" of the current service (possibly moving some circuits around) you can simply connect to one of the hots on the L14-50R on the end of your TT30P to L14-50R adapter cord, leaving the other one disconnected (and connecting neutral and ground, of course.)
    – Ecnerwal
    Commented Nov 11, 2021 at 17:10

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