Author Topic: Re-wire generator plug  (Read 759 times)

SpacemanSpiff

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Re-wire generator plug
« on: December 16, 2021, 09:45:19 AM »
The house we purchased earlier this year is set up to be able to plug in a 30-amp generator, including a cord with a 30 amp (L14-30P) male plug on the side of the house.  I also have a generator that I was hoping to be able to use to power the essentials (lights, sump pump, gas furnace, tv, modem/router - nothing with a heavy load like electric furnace or electric dryer, etc) if/when the power goes out.

However, the generator only has a 20A (L14-20) receptacle.  I'm thinking I'll replace the L14-30P plug on the cord with a L14-20P (https://www.homedepot.com/p/AC-WORKS-AC-Connectors-NEMA-L14-20P-20-Amp-125-250-Volt-4-Prong-Assembly-Locking-Male-Plug-ASL1420P/303108448).  Anything I'm missing before I do such?

There is a lockout on the secondary box in the basement that the cord leads to, so I would be working on a cord that is not hot.  Additionally, I always double check with a tester even after shutting off the applicable breaker.

uniwelder

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Re: Re-wire generator plug
« Reply #1 on: December 16, 2021, 11:38:52 AM »
I'm posting to follow and learn.  From what I see, it seems both styles are 4 wire plugs/receptacles, so you'll get both 120 and 240 volts output.  Curious what others say about replacing the plug.  In my simple mind, since you're going to a lower amperage, everything should be fine to swap.  I assume the cord routes to a 30 amp breaker, so I don't think there is a reason to downsize to 20 there.

SpacemanSpiff

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Re: Re-wire generator plug
« Reply #2 on: December 16, 2021, 01:17:32 PM »
uniwelder - That was exactly my logic.  Both styles are indeed 4 wire (1 ground, 1 neutral, 2 hot), and the cord does indeed go to a 30 amp breaker.

As far as whether it's too much load on the generator itself, it's supporting the same items it supported at our last house via 3 heavier duty extension cords (and a power strip or 2), but with the addition of the full lighting system in the house (instead of a few strategically placed lamps).  Given literally every light fixture in our house is now LED, I'm thinking the load from also having the lights is basically negligible.

Ripple4

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Re: Re-wire generator plug
« Reply #3 on: December 17, 2021, 06:09:24 AM »
The house we purchased earlier this year is set up to be able to plug in a 30-amp generator, including a cord with a 30 amp (L14-30P) male plug on the side of the house.  I also have a generator that I was hoping to be able to use to power the essentials ... Anything I'm missing before I do such?

One thing to look at is if the generator you have has the neutral wire connected to the ground wire inside the generator. OSHA requires portable generators have this, because it a primary power source on the job site. however when connected to a house the generator is a 'separately derived power system', check out 20xx NEC250.30 and 250.34. when I setup my 120/240 20 amp portable generator (converted to natural gas and dedicated to backup power use) I had to open this connection in my generator wiring cover, so that the only ground to neutral connection was inside the load center. I have two Coleman 10-circuit prewired manual transfer switches that feed solar and generator power into my home. if you fail to do this the ground (frame of the generator) could carry some of the neutral current.

https://www.ecmweb.com/national-electrical-code/code-basics/article/20890358/grounding-and-bonding-of-separately-derived-systems

BudgetSlasher

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Re: Re-wire generator plug
« Reply #4 on: December 17, 2021, 06:36:13 AM »
Presuming all the wiring in your house was sized/done correctly and that you generator is correctly setup (as mentioned above) I do not see an issue.

Quickly Googling the plug types you mentioned it looks like the RV'ing world (and others) is full of adapters between the two or cords that have mixed heads, likely for the opposite purpose hooking an RV that can handle 30A to a source that can provide only 20A.

SpacemanSpiff

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Re: Re-wire generator plug
« Reply #5 on: December 19, 2021, 07:39:19 PM »
Presuming all the wiring in your house was sized/done correctly and that you generator is correctly setup (as mentioned above) I do not see an issue.

Quickly Googling the plug types you mentioned it looks like the RV'ing world (and others) is full of adapters between the two or cords that have mixed heads, likely for the opposite purpose hooking an RV that can handle 30A to a source that can provide only 20A.

That sounds like the same purpose... hooking up our house that can handle 30A to our generator that can only provide 20A?

SpacemanSpiff

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Re: Re-wire generator plug
« Reply #6 on: December 19, 2021, 07:50:15 PM »
The house we purchased earlier this year is set up to be able to plug in a 30-amp generator, including a cord with a 30 amp (L14-30P) male plug on the side of the house.  I also have a generator that I was hoping to be able to use to power the essentials ... Anything I'm missing before I do such?

One thing to look at is if the generator you have has the neutral wire connected to the ground wire inside the generator. OSHA requires portable generators have this, because it a primary power source on the job site. however when connected to a house the generator is a 'separately derived power system', check out 20xx NEC250.30 and 250.34. when I setup my 120/240 20 amp portable generator (converted to natural gas and dedicated to backup power use) I had to open this connection in my generator wiring cover, so that the only ground to neutral connection was inside the load center. I have two Coleman 10-circuit prewired manual transfer switches that feed solar and generator power into my home. if you fail to do this the ground (frame of the generator) could carry some of the neutral current.

https://www.ecmweb.com/national-electrical-code/code-basics/article/20890358/grounding-and-bonding-of-separately-derived-systems

Thanks.  Had no idea that was something to worry about - definitely don't want the generator/its frame carrying current.

Also, you converted your portable generator to natural gas? Had no idea that was a thing, but a quick internet search makes it seem like it's relatively common.  I will have to look into that...

Syonyk

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Re: Re-wire generator plug
« Reply #7 on: December 19, 2021, 10:27:09 PM »
Anything I'm missing before I do such?

Nope.

Your generator's breakers should trip at the 20A rating of the outlet.  The cord is rated for 30A, so will be fine, as will everything house side.  As long as you can get the 20A outlet to take the 30A cord size, all will work fine.  You'll trip the generator at its limit, not the house limit.

However, may I suggest building an adapter instead?  Get a 20A male, 30A female, and a short chunk (1' or whatever, unless you can find a free scrap) of 10AWG - and then just wire them up.  No need to cut up a perfectly good extension cord, and if you get a 30A generator, easy to replace things.

Ripple4

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Re: Re-wire generator plug
« Reply #8 on: December 20, 2021, 04:11:24 PM »
Also, you converted your portable generator to natural gas? Had no idea that was a thing, but a quick internet search makes it seem like it's relatively common.  I will have to look into that...

Yes, I bought a kit from century fuel products and made a custom single fuel carburetor. The main part is a so-called demand regulator, it reads the vacuum 'signal' from a venturi in the intake path, and adds more fuel as the vacuum decreases, pretty clever. on the budget side of things there are super cheap imported 'dual fuel' carburators for the honda GX200cc clone engines on ebay for $30. keep in mind that propane or NG fumigation will reduce output ~20%. the gaseous fuel displaces air more than liquid gasoline.

SpacemanSpiff

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Re: Re-wire generator plug
« Reply #9 on: December 24, 2021, 06:55:31 PM »
Anything I'm missing before I do such?

Nope.

Your generator's breakers should trip at the 20A rating of the outlet.  The cord is rated for 30A, so will be fine, as will everything house side.  As long as you can get the 20A outlet to take the 30A cord size, all will work fine.  You'll trip the generator at its limit, not the house limit.

However, may I suggest building an adapter instead?  Get a 20A male, 30A female, and a short chunk (1' or whatever, unless you can find a free scrap) of 10AWG - and then just wire them up.  No need to cut up a perfectly good extension cord, and if you get a 30A generator, easy to replace things.

Glad to hear. 

I'm probably going to do just that, except instead of constructing my own Franken-cable, it looks like there are adapters pre-made specifically for this that cost about the same as the individual supplies:

https://www.amazon.com/MPI-Tools-L14-20P-L14-30R-Generator/dp/B01MUDTISM/ref=asc_df_B01MUDTISM/?tag=hyprod-20&linkCode=df0&hvadid=167151917227&hvpos=&hvnetw=g&hvrand=5741412646297082340&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1027028&hvtargid=pla-310872949171&psc=1