Model 3 with wall charger 10guage wire and 40A breaker

[Murryy79]

Hello -
At work was discussing with other proud owners of Tesla and the wall charging topic came up which got me concerned about my circuit.

So we re-hired an electrician who in the past have done some ceiling recessed lighting work in my house.

For installation of Tesla wall charger in my garage he used a 40A breaker and 10guage wire. I know nothing about all these electrical stuff.

Now when having discussion with my co workers I am concerned that my Mobile Tesla app says 32A and almost everywhere on the Internet I can find 10guage wire is suitable for upto 30A.

Now why question is - is there a high risk of excessive heat and fire hazard?

Will charging at 29A or even lower 24A(80% of 30A) should be safer option until I can get someone to replace the 10guage with 8 or 6 gauge in the aluminum conduit?

Note : in the Tesla Mobile app I can lower the Amps settings. Max is 32A

Thanks to all for reading this post and sharing your knowledge and experience.

 

[frankusb]

Yes, you should charge at 24A. You should also replace the wire or the breaker.

 

[jjrandorin]

For installation of Tesla wall charger in my garage he used a 40A breaker and 10guage wire. I know nothing about all these electrical stuff.

If its THHN in conduit (which since you mention its in conduit, is likely) its fine and you dont have to replace anything.

Check this website that I believe one of our regular members ( @Cosmacelf ) maintains:

Advice for EV Charging in North America

Advice for EV Charging in North America

carcharging.us

(chart from above website)

Charge Amps	Breaker Size	NM-B	UF-B	MC	THHN/ Conduit
EVSE	Wire Gauge (Ground Gauge)
24A	30A	10	10	12	12
32A	40A	8	8	10	10
40A	50A	6	6	8	8 (10)
48A	60A	4	4	6	6 (10)
80A	100A	N/A	N/A	N/A	3 (8)
Environment:	Dry	Wet	Dry	Wet*

40amp breaker = 32amp charging = 10 gauge THHN in conduit (which is the most likely wiring to be installed by an electrician in conduit).

Since you mention you dont know much about the electrical, and you hired an electrician to do it for you, the assumption should be that if you gave them all the information ("I am going to use this for a continuous load / EV charging") and didnt tell them something like "EV charging, no, thats not what I am doing... I am using this for a welder, yep thats it") that it should be done properly.

It appears to be correct to me, from the information you provided.

 

[Cosmacelf]

If its THHN in conduit (which since you mention its in conduit, is likely) its fine and you dont have to replace anything.

Check this website that I believe one of our regular members ( @Cosmacelf ) maintains:

Advice for EV Charging in North America

Advice for EV Charging in North America

carcharging.us

(chart from above website)

EVSE	Wire Gauge (Ground Gauge)
Charge Amps	Breaker Size	NM-B	UF-B	MC	THHN/ Conduit
24A	30A	10	10	12	12
32A	40A	8	8	10	10
40A	50A	6	6	8	8 (10)
48A	60A	4	4	6	6 (10)
80A	100A	N/A	N/A	N/A	3 (8)
Environment:	Dry	Wet	Dry	Wet*

40amp breaker = 32amp charging = 10 gauge THHN in conduit (which is the most likely wiring to be installed by an electrician in conduit).

Since you mention you dont know much about the electrical, and you hired an electrician to do it for you, the assumption should be that if you gave them all the information ("I am going to use this for a continuous load / EV charging") and didnt tell them something like "EV charging, no, thats not what I am doing... I am using this for a welder, yep thats it") that it should be done properly.

It appears to be correct to me, from the information you provided.

Ugh. I am so embarrassed. I thought I had fixed this on my site, but apparently not. I was using the wrong temperature rating column from the ampacity charts when I originally put this together. Partly I blame the NEC which changed the code somewhere along the way, and partly I blame myself for playing amateur electrician, the NEC is complex and there are a bunch of subtle rules. Anyways, for typical(*) equipment installs you should use the 75 degree column in ampacity charts even though THHN wire is rated for 90 degrees since the termination points will typically only be rated for 75 degrees (except for NM-B and UF-B, where you use the 60 degree column). Anyways, here's the correct abbreviated chart from my website now:

So 10 gauge wire can only be used with a 30A breaker.

(*) - there are a bunch of exceptions which would modify any ampacity table including having more than three current carrying conductors in a conduit, higher than normal ambient temperatures, and non-typical equipment with lower temperature ratings. Technically, the NEC says to use the 60 degree column unless the termination points (breaker and EVSE in this case) explicitly state a temperature rating, but the actual normal practice seems to be to assume 75 degrees unless otherwise stated.

 

[Cosmacelf]

Hello -
At work was discussing with other proud owners of Tesla and the wall charging topic came up which got me concerned about my circuit.

So we re-hired an electrician who in the past have done some ceiling recessed lighting work in my house.

For installation of Tesla wall charger in my garage he used a 40A breaker and 10guage wire. I know nothing about all these electrical stuff.

Now when having discussion with my co workers I am concerned that my Mobile Tesla app says 32A and almost everywhere on the Internet I can find 10guage wire is suitable for upto 30A.

Now why question is - is there a high risk of excessive heat and fire hazard?

Will charging at 29A or even lower 24A(80% of 30A) should be safer option until I can get someone to replace the 10guage with 8 or 6 gauge in the aluminum conduit?

Note : in the Tesla Mobile app I can lower the Amps settings. Max is 32A

Thanks to all for reading this post and sharing your knowledge and experience.

If he really did use 10 gauge wire, you should replace the breaker with a 30A breaker, and set your charge rate to 24A.

Or, re-wire with 8 gauge (since it sounds like you have EMT, metal conduit?). With 8 gauge, you'd be able to use a 50A breaker and charge at 40A. Or go whole hog, use 6 gauge, 60A breaker and charge at 48A.

 

[DuncanM]

Hello -
At work was discussing with other proud owners of Tesla and the wall charging topic came up which got me concerned about my circuit.

So we re-hired an electrician who in the past have done some ceiling recessed lighting work in my house.

For installation of Tesla wall charger in my garage he used a 40A breaker and 10guage wire. I know nothing about all these electrical stuff.

Now when having discussion with my co workers I am concerned that my Mobile Tesla app says 32A and almost everywhere on the Internet I can find 10guage wire is suitable for upto 30A.

Now why question is - is there a high risk of excessive heat and fire hazard?

Will charging at 29A or even lower 24A(80% of 30A) should be safer option until I can get someone to replace the 10guage with 8 or 6 gauge in the aluminum conduit?

Note : in the Tesla Mobile app I can lower the Amps settings. Max is 32A

Thanks to all for reading this post and sharing your knowledge and experience.

You should replace the outlet with a NEMA 14-30 and then use the appropriate adapter for your TMC. The breaker should be replaced with a 30amp or 20 amp. You can probably made these changes yourself with little risk.

The NEMA 14-30 adapter for the TMC will auto set the max amps to 24.

 

[DuncanM]

You should replace the outlet with a NEMA 14-30 and then use the appropriate adapter for your TMC. The breaker should be replaced with a 30amp or 20 amp. You can probably made these changes yourself with little risk.

The NEMA 14-30 adapter for the TMC will auto set the max amps to 24.

I meant to remove the mention of a 20amp breaker.

 

[davewill]

If he really did use 10 gauge wire, you should replace the breaker with a 30A breaker, and set your charge rate to 24A.

Or, re-wire with 8 gauge (since it sounds like you have EMT, metal conduit?). With 8 gauge, you'd be able to use a 50A breaker and charge at 40A. Or go whole hog, use 6 gauge, 60A breaker and charge at 48A.

@Murryy79 , use 6 gauge, even if you're using a 14-50 and a 50a breaker for now. I say this as a guy who's got a 6-50 on 8ga NM-B (40a breaker). Works fine, but I would have liked 48a (or even 40a) charging as an option. My install was so many years ago, that 32a charging was seen as total overkill, (my LEAF at the time was limited to 16a) and it never even occurred to me to go bigger.

I know better now. When I did my second install of a 14-50 a few years back, I did use 6ga THHN. 32a charging is still fine, but if I ever do decide to get a wall connector, I can take advantage of it, at least on one side of the garage.

 

[walt_ohio]

Hello -
At work was discussing with other proud owners of Tesla and the wall charging topic came up which got me concerned about my circuit.

So we re-hired an electrician who in the past have done some ceiling recessed lighting work in my house.

For installation of Tesla wall charger in my garage he used a 40A breaker and 10guage wire. I know nothing about all these electrical stuff.

Now when having discussion with my co workers I am concerned that my Mobile Tesla app says 32A and almost everywhere on the Internet I can find 10guage wire is suitable for upto 30A.

Now why question is - is there a high risk of excessive heat and fire hazard?

Will charging at 29A or even lower 24A(80% of 30A) should be safer option until I can get someone to replace the 10guage with 8 or 6 gauge in the aluminum conduit?

Note : in the Tesla Mobile app I can lower the Amps settings. Max is 32A

Thanks to all for reading this post and sharing your knowledge and experience.

10 Gauge wire is only for 30 amp circuits. Overheating of the 10 gauge wire is very likely, charge at 24 amps.. As mentioned before change breaker or wire. I use 6 gauge and a 50 amp breaker

 

[Murryy79]

Thanks everyone for your response.
I will see if I can pass thru 6guage wire inside metal conduit and rewire to the wall charger and use 40A.or 60A breaker whichever works the best