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Extension Cord Question

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What kind of plug is your oven receptacle? One way doing this is to buy a 30' nema 14-50 to nema 14-50 extension cord. They are available at RV stores or on amazon. Search for camco 50a extension cord. You then make a pigtail adapter from the oven plug to a female 14-50 receptacle. This way you have a useful nema 14-50 50a extension cord and a way to plug into the oven plug.
 
I need a quick way of building an extension cord to plug into an oven female wall plug and to the male NEMA 14-50 side of the UMC. Around 50 feet to charge my Model S.

Was thinking of buying a female NEMA 14-50 wall plug and connect a 8-3 cable to it and then create a junction box to plug the male connector (don't seem to find a simple male NEMA 14-50 connector in-store, just a pre-stubbed version).

This is for very very very rare use. any electricical advice?

You will probably have to look at wire ratings, but most likely you will need 6/3 cable to make a 50A cord. And if you want 14-50 you really should have 4 conductors. And don't use ROMEX use SOOW (or similar) cord for an extension.

I plan on making a 30A extension cord with a NEMA 10-30 adapter from Tesla for the UMC. 50' of 8/3 SOOW cord. A NEMA 10-30 receptical and a 10-30 plug (ill also make a short ~6" long 10-30R to 14-30 plug adapter with a big "FOR TESLA MODEL S CHARGING ONLY" TAG with "NO NEUTRAL CONDUCTOR PRESENT" on the other side.
 
You will probably have to look at wire ratings, but most likely you will need 6/3 cable to make a 50A cord. And if you want 14-50 you really should have 4 conductors. And don't use ROMEX use SOOW (or similar) cord for an extension.

I plan on making a 30A extension cord with a NEMA 10-30 adapter from Tesla for the UMC. 50' of 8/3 SOOW cord. A NEMA 10-30 receptical and a 10-30 plug (ill also make a short ~6" long 10-30R to 14-30 plug adapter with a big "FOR TESLA MODEL S CHARGING ONLY" TAG with "NO NEUTRAL CONDUCTOR PRESENT" on the other side.

I agree. If you are going 50 feet you need '6/4'...you will be pulling 40 amps thru that relatively long run. The cost may be $50 more than similar '8' wire but it will be a lot safer.
 
Thanks for your input guys, my oven female plug seems to be a NEMA 14-50. It's the same shape/form as the NEMA 14-50 that my electrician installed for the UMC charger. It says 250V on the face plate and 125V on the other and then 50A close to the bottom of the face plate. My oven breakers is a 40A so I was thinking of setting the amps to 30A on my S not to take any chance.
 
Actually, you can use 32 amps from a 40 amp breaker. I don't believe there exists a 40 amp receptacle, so the electrician probably used the next size up receptacle, but probably used 40 amp wire and thus a 40 amp breaker. Just dial down the tesla to 32 amps and you'll be ok. And you could just use a standard 50a extension cord with nema 14-50 ends available from RV stores.
 
That circuit isn't to code. You can't put a NEMA 14-50 on a 40A breaker. For sure dial the current back to 30A. But also consider getting an electrician to look at it...

Actually, under NEC you can. You can't place a 30A receptacle on a 40A or 50A breaker, but you can protect a larger-rated set of conductors and receptacles with a smaller breaker, provided that you do not attach a load rated for higher than that.

It all gets confusing, I know... but electric stoves connected with cord-and-plug are permitted providing their nameplate only calls for a 40A circuit (and many do). However, it violates NEC to connect the Tesla to a 14-50R on a 40A breaker, because Tesla's nameplate for the system is rated at 50A.

Also, I addressed this in the same thread in the charging forum, but I'll address it here too... #8 wire is just fine for a 50A circuit as long as it's not NM-B (Romex) or flex cable -- #8 wire in conduit is rated for 50A just fine. If NM-B, you must use #6 because NEC requires you to use the 60 degC rating, despite that conductors inside are rated for 90 degC. If SOOW, things get a bit complex. You can use a 6/4 to power a Tesla because the "B" column of NEC table 400.5(A) allows for 55A rating when only 2 conductors of a 4-conductor cable are carrying current. But if you use that cord with an RV, it may not be to code because using the neutral, you have 3 current-carrying conductors and it's limited to 45A.

Bottom line, if you build an extension cord, use 14-50P and 14-50R on a 6/4 cable/cord (SOOW preferred for flexibility -- NM-B/Romex is not rated for temporary use).
 
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Actually, under NEC you can. You can't place a 30A receptacle on a 40A or 50A breaker, but you can protect a larger-rated set of conductors and receptacles with a smaller breaker, provided that you do not attach a load rated for higher than that.

It all gets confusing, I know... but electric stoves connected with cord-and-plug are permitted providing their nameplate only calls for a 40A circuit (and many do). However, it violates NEC to connect the Tesla to a 14-50R on a 40A breaker, because Tesla's nameplate for the system is rated at 50A.

Also, I addressed this in the same thread in the charging forum, but I'll address it here too... #8 wire is just fine for a 50A circuit as long as it's not NM-B (Romex) or flex cable -- #8 wire in conduit is rated for 50A just fine. If NM-B, you must use #6 because NEC requires you to use the 60 degC rating, despite that conductors inside are rated for 90 degC. If SOOW, things get a bit complex. You can use a 6/4 to power a Tesla because the "B" column of NEC table 400.5(A) allows for 55A rating when only 2 conductors of a 4-conductor cable are carrying current. But if you use that cord with an RV, it may not be to code because using the neutral, you have 3 current-carrying conductors and it's limited to 45A.

Bottom line, if you build an extension cord, use 14-50P and 14-50R on a 6/4 cable (SOOW preferred for flexibility -- NM-B/Romex is not rated for temporary use).

That's pretty technical but really precise. Thank you. I contacted the electricain that installed my NEMA 14-50 circuit at home and he suggested I use SOOW cable and offered to order the parts from a specialized store near my house. He didn't talk about cable size (6/4 or 8/4). I find it strange that I need 6/4 since for my permanent set up at home, he used loomex 8/3 cable. My dad freaked out when he asked the local Rona clerks that scared the hell out of him. The extension will be used at his place... so I decided to play safe and ask a professional which you seem to be FlasherZ.

I'll dial down to 30A