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Open Roads Forum  >  Tech Issues

 > DIY 50 amp to 20 amp pigtail

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KnowNuthin

Centennial, CO

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Posted: 11/07/22 07:30am Link  |  Quote  |  Print  |  Notify Moderator

I want to plug my tractors block heater into our 50 amp RV service for the upcoming winter months…

Our panel has 1 - 50 amp and 2 - 20 amp breakers… both 20 services are taken and currently used year round… (chicken heat lamps, water bowl heaters etc.)…

What I’m envisioning is a 50 amp plug with a 3 wire pigtail connected to the common, neutral and one hot leg… leaving the second hot leg vacant…

This would give me 120v 50 amp at the pigtail end… no?

This would be used STRICTLY for a 600 watt engine block heater…

Is this a bad, terrible or workable idea?


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enblethen

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Posted: 11/07/22 07:44am Link  |  Quote  |  Print  |  Notify Moderator

Your 50 amp should be a double pole breaker.
I think it is a bad idea for what you are thinking.
I would suggest getting thin breaker with two 20-amp breakers and installing a new receptacle. Some call breakers, wafer or tandem.


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MitchF150

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Posted: 11/07/22 08:34am Link  |  Quote  |  Print  |  Notify Moderator

You can buy what you need off the shelf. Get a 50a-30a adapter. Then get a 30a-20a adapter. People do this all the time when plugging in their 30 or 20a only rigs..

Difference is that the rigs themselves will have their own 30-20a breaker, so it's still protected to that amount.

If you just plug right into the adapter with the 600w heater, it'll still be connected to the 50a breaker. It'll work just fine, just not pop until it exceeds the 50a breaker if something grounds out for some reason.

Good luck! Mitch


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Dutch_12078

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Posted: 11/07/22 09:38am Link  |  Quote  |  Print  |  Notify Moderator

Generator/RV 50 Amp 125/250-Volt NEMA 14........mp 5-15/20R T-Blade Connector RV Adapter


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toedtoes

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Posted: 11/07/22 09:50am Link  |  Quote  |  Print  |  Notify Moderator

Would this work for you? It has a built in circuit breaker for added protection:
50amp to 4x 15/20amp adapter


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ktmrfs

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Posted: 11/07/22 10:11am Link  |  Quote  |  Print  |  Notify Moderator

KnowNuthin wrote:

I want to plug my tractors block heater into our 50 amp RV service for the upcoming winter months…

Our panel has 1 - 50 amp and 2 - 20 amp breakers… both 20 services are taken and currently used year round… (chicken heat lamps, water bowl heaters etc.)…

What I’m envisioning is a 50 amp plug with a 3 wire pigtail connected to the common, neutral and one hot leg… leaving the second hot leg vacant…

This would give me 120v 50 amp at the pigtail end… no?

This would be used STRICTLY for a 600 watt engine block heater…

Is this a bad, terrible or workable idea?


there is a potential safety/fire issue. I'm going to assume the cord to the block heater is a 12ga cord. Now you hook this up and end up with a low resistance high current draw. The breaker won't trip till it exceeds 50A, so you could end up with 50a through a 12ga cord, NOT a good idea, it would get quite hot, maybe even hot enough to melt the insulation and start a fire.

you want the upstream breaker in this case to be a 15A or 20A breaker.


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pianotuna

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Posted: 11/07/22 10:35am Link  |  Quote  |  Print  |  Notify Moderator

Hi,

Build a 50 to 20 break out box. Have a 15 amp circuit breaker "in line" (or in the break out box.

My own break out box has one 30 amp (l1) and two 20 amp (l2) breakers with plugs. It is, of course, unbalanced if it is fully loaded. (i.e. 30 amps one leg, and 40 amps other leg).


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KnowNuthin

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Posted: 11/07/22 10:37am Link  |  Quote  |  Print  |  Notify Moderator

My original idea is officially axed... somewhere in the back of my brain having 50a running through an extension cord didn't seem like a good idea, but, hey... I'm not an electrician...

I like the options presented by Dutch and Toed... it appears both of them are limited to 20a ... a much better solution...

One is more simple, the other offers the ability to close the front of my 50a box...

Mitch's idea works too... I already have the 50a - 30a dogbone...

decisions... decisions...

Cummins12V98

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Posted: 11/07/22 10:39am Link  |  Quote  |  Print  |  Notify Moderator



That will do the job but I would rather have what was mentioned earlier as this will give you the 30A/120V option.

"You can buy what you need off the shelf. Get a 50a-30a adapter. Then get a 30a-20a adapter."


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toedtoes

California

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Posted: 11/07/22 11:08am Link  |  Quote  |  Print  |  Notify Moderator

KnowNuthin wrote:

My original idea is officially axed... somewhere in the back of my brain having 50a running through an extension cord didn't seem like a good idea, but, hey... I'm not an electrician...

I like the options presented by Dutch and Toed... it appears both of them are limited to 20a ... a much better solution...

One is more simple, the other offers the ability to close the front of my 50a box...

Mitch's idea works too... I already have the 50a - 30a dogbone...

decisions... decisions...


Any of them will work. I like the one I posted simply because it has internal circuit breakers. And it's only one connection versus the two connection points with the 50-30 to 30-20. But that's just personal preference.

I'd consider potential use off season for the adapter. Would the 50-20 or the 30-20 give you any options for use when RVing?

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