Amperage

[KArnold]

Warning - newb question.

I had an electrician come out to setup a garage 220-volt plug. I have a hot tub that I no longer use and he suggested running that 6-gauge wire to the garage and connect it to a nema 14-50 outlet. For my needs i think even a 30-amp plug would be fine but he said "that should push 100 amps easily". So I'm hoping this would work for a rated 50 amp nema 14-50 plug.

But my newbie spider senses came alive. I would think you would want 4-gauge for 100 amp or close to it. Yes?

Isn't it the device itself (in this case, a MS) that determines amperage draw? Can I tell the MS to not draw more than 50 amps? Is there a way by looking at a panel to determine the safe rated amperage? I did not see any labels on the panel but we didn't take the cover off either - I believe he was speaking from his electrical experience on hot tubs in general.

I also assume that if my panel/wiring did support 100 amps (which I can't see needing), I would want an outlet different than the 14-50?

I did not hire the guy.

Thanks in advance.

 

[Derek Kessler]

Stick a 50A breaker in there — you don't want anything greater than that for an outlet rated at 50A, and the Tesla UMC won't pull more than 40A from a 14-50 anyway (80% of 50A). Not does the UMC support any higher-amperage plugs.

That said, if you get a Tesla HPWC, that can take up to 100A for charging at up to 52 miles range per hour.

 

[TexasEV]

Here is Tesla's recommendation for installing the 14-50 outlet for home charging:
https://www.tesla.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf

Note there is no such thing as 220V although it's commonly called that for historical reasons. It's 240V.

 

[gregd]

Your spider sense is serving you well. #6 wire is only good for a 50 amp socket and breaker, with 40 amps the actual (continuous) draw from the car. I ran #4 wire to my 14-50 socket, for ease of upgrade later, but the socket is still the limit, and the breaker needs to match the socket. Even #4 wire won't quite get me to a 100 amp breaker, if I recall.

If your electrician insists that #6 can support 100 amps, you might consider a different electrician.

 

[BerTX]

Your spider sense is serving you well. #6 wire is only good for a 50 amp socket and breaker, with 40 amps the actual (continuous) draw from the car. I ran #4 wire to my 14-50 socket, for ease of upgrade later, but the socket is still the limit, and the breaker needs to match the socket. Even #4 wire won't quite get me to a 100 amp breaker, if I recall.

If your electrician insists that #6 can support 100 amps, you might consider a different electrician.

I agree with all of this.

If it is #6 THHN in conduit you can go to 60A to connect the Wall Connector and run it at 48A charge rate.

 

[FlyF4]

Here is Tesla's recommendation for installing the 14-50 outlet for home charging:
https://www.tesla.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf

Note there is no such thing as 220V although it's commonly called that for historical reasons. It's 240V.

You beat me to it The old guys (from my era) call it 110 and 220 even when they have been electricians for years. Good point, in practically all of America, it is 120 and 240. At least been that way for several decades as you know.

And to the OP, wire gauge is also going to depend on the distance that the current needs to travel from the panel to the destination. The longer the distance, the larger the wire.

 

[sdorn]

My electrician used #1 SER for the 100 amp run from my basement electrical panel to the subpanel they installed in the garage (about 40 feet). They used #2/3 copper Romex for the very short (~1 ft) run from the subpanel to the HPWC.

 

[tga]

My electrician used #1 SER for the 100 amp run from my basement electrical panel to the subpanel they installed in the garage (about 40 feet). They used #2/3 copper Romex for the very short (~1 ft) run from the subpanel to the HPWC.

FYI, #2 copper Romex (NM-B) is insufficient for a 100A circuit (80A charging). NM-B is only rated to go to 60 deg C, which limits you to 95A. To get 100A out of #2 copper, you need wire rated to 75 deg C (SER or THHN in conduit would work).

 

[sdorn]

FYI, #2 copper Romex (NM-B) is insufficient for a 100A circuit (80A charging). NM-B is only rated to go to 60 deg C, which limits you to 95A. To get 100A out of #2 copper, you need wire rated to 75 deg C (SER or THHN in conduit would work).

Yes, they only put a 90 amp breaker in the subpanel as my car has the 72 amp charger, so it is 100 amp from the main panel to the subpanel, but only 90 amp from the subpanel to the HPWC.

 

[tga]

Yes, they only put a 90 amp breaker in the subpanel as my car has the 72 amp charger, so it is 100 amp from the main panel to the subpanel, but only 90 amp from the subpanel to the HPWC.

Perfect. I saw 100A in your prior post and thought you meant all the way to the HPWC, not just to the subpanel.

 

[Solarman004]

@KArnold , take a look at this wire sizing chart: Ampacity Charts
While a breaker can protect your equipment, its primary function is to protect the wire and prevent fire. The breaker rating must be lower than the wire rating.
So the electrician's comment of running #6 AWG wire on a 100 amp circuit, is not only wrong, it's a code violation and dangerous.
A proper NEMA 14-50 connection is spelled out in the installation manual: 50 amp breaker with #6 or larger copper wire. If you want to wire for 72 amp HPWC, you need a 90 amp breaker (72/0.8) and #3 copper wire.
Don't ever allow a breaker that is oversized for the wire gauge- that's how house fires can start.

 

[xyeahtony]

Most people here aren't electricians and even they know that 100amps on a #6 gauge wire is wrong/incorrect. Even the wiring charts at Lowes/Home Depot point this out. Sounds to me this guy had no idea what he was doing (the so called electrician).

Simple groundrules:

NEMA 14-50 use a 50 amp breaker, 6 gauge THHN wire. Car will draw no more than 40 amps max, which is 80% circuit capacity which is code limit in the USA (canada limits max draw to 32A)

Tesla Wall Connector use 60 amp breaker, 6 gauge THHN wire. Car will draw 48 amps.

Tesla Wall Connector with 90 amp breaker, 3 gauge THHN. Car will draw 72 amps max (unless you dont have high amperage charger, in which case it'll only draw 48 amps max)

Connecting a NEMA 14-50 ( a 50 amp outlet to a 100 amp circuit ) is a massive code violation and is asking for trouble. If there was a fire that occurred and inspectors saw this, doubt homeowners insurance would pay for faulty wiring.

 

[SomeJoe7777]

Don't forget that if you use 75 degree temperature ratings for a wire to get the desired amperage that all the terminations (receptacle, breaker, sub panel) must also be rated at that same temperature or higher to legally use that temperature and amperage rating for the circuit. THHN at 75 degrees does you no good if the receptacle terminals are only rated 60 degrees.

 

[scottm]

If you're using mobile charger in the garage and plan to be bringing that same mobile charger around with you a lot, then invest in a very high quality nema 14-50 receptacle. Don't go for the cheap-o Home Depot kitchen stove jobbie.