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Yeah that's a fire hazard, #10 is rated for 30A max, but derated to 80%, or 24A for continuous. Theoretically your breaker should break after a few minutes at 30A
http://www.usawire-cable.com/pdfs/nec ampacities.pdf
cpa
Active Member
I did not bother to read the article. The historical wording of the law that allows the credit is that the credit is not allowed for Alternative Minimum Tax. Yes, the $7,500 BEV credit upon purchase of your Tesla is. Maybe the way they are changing the wording in the law to allow this credit against AMT.
So, if a taxpayer is subject to AMT, he can wave the EVSE credit goodbye. If your income is north of $650,000 or so, the chances are that your regular tax exceeds AMT anyway, so you will get to utilize the 30% EVSE credit. But if your income is like many who can purchase a Tesla, the EVSE credit will evaporate.
This is my understanding of the law, and how it applied in my case and the case of a client.
If you leave the car at 40A the breaker will kick after 8-10 minutes. I have seen breakers rated at 30 that won't hold at 25. While traveling cross country we stayed at a place with a 30A plug on a 30A breaker, dryer plug. We had no problem charging at 30A. My guess is if your electric system is in good shape it is possible to charge at rated current and have a slight margin. As you point out though it is better to leave a large margin in case of poor connection nicked wire or bad breaker.
That's just the breaker, and it sounds like it's defective. It says nothing about the temperature of the wire and connectors in the path, which is where the fire hazard is. At 40 amps I think there's a good chance you might melt the romex insulation and get a short inside the wall. #10 romex is too small for 40 amps continuous draw.
Fire hazard.
The margin isn't for a poor connection or nicked wire. It's what the electrical code demands to prevent a fire hazard (however small or large that chance is). I forgot which way it goes (FlasherZ would correct me) it's either 80% of the breaker loading, or your breaker is supposed to handle 125% of the continuous load (the math is the same, but the code specifies it one specific way).
If you used the Tesla 30A dryer plug, your car automatically de-rated it to 24A. If you used a NEMA 14-50 to xx-xx adapter (whatever model of 30A dryer you had), then you could've [unsafely] set the car to charge at the full 30A. While I understand that you feel comfortable breaking the code, but you shouldn't advertise other people to do the same.
FlatSix911
Porsche 918 Hybrid
I am confused after reading the thread and the NEC allowable ampacities guide ...
It seems that using a conductor with a higher temp rating will solve the problem.
i.e. A Type THHN #10 conductor is rated for 40A and derated for 32A continuous load.
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If you have #10 THHN and components rated for 90C, sure. That's special wire that is run through conduits only. Do you see single wires run through metal/pvc conduit?
If you have nm-b/romex cable in the walls like every other normal house, then you should be using the 60C column, which is 30A/24A continuous
FlatSix911
Porsche 918 Hybrid
Thanks. I am not the OP here, but the explanation makes sense if you are using existing household wiring.
+1 !
Solar
Please don't leave any family members (and CERTAINLY pets!) at home while charging. Also, I would highly recommend an off-site back-up for your data.
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mspohr
Well-Known Member
It sounds like it would be relatively easy (and cheap) to upgrade your installation to a safe one.
Just invest $12 in a new 50 amp breaker and a few dollars in a short piece of 6/3 Romex wire and you should be able sleep well (even when charging at 40 amps).
I did it myself and my breaker box was inside the house. Cost me about 75$ in parts or less since I had a few around the house. Its just a dryer outlet with a little larger breaker.
No one is saying electricians are stupid. But, if you tell them "I want an RV outlet in my garage" they know it's for an EV, since very few home garages can accommodate an RV. If you say "I want to install a 50A outlet for a kiln/welder in my garage" it's going to be more plausible. It's the smarter ones that figure out you've bought an expensive electric car and jack up the price.
Do your homework and call them on their bull****. I'm installing a whole new load center plus multiple new circuits for a half to a quarter of the cost you guys are paying an electrician for one circuit. The parts for the 14-50 circuit alone come to a whopping $40 at the local home depot. Add $3 per additional foot it is away from the load center.
I did, they backpedaled. It was a waste of time.
I emailed the Tesla "authorized" installers, got $1,200-1,600 as a starting point over email. When I said parts cost $200 at HD, permits are $100, and you're charging me $1,300 for labor on a 2-3 hour job (I described the job and emailed pics, all the other contractors said they don't need to come out to see it, pics and details were good enough) - they replied with, "well we've had jobs as low as $400" and [something along the lines of] "we're playing it safe now, it might cost less". Then WTF did you start with $1,600?
They were not invited into my house, obviously.
I actually did my own install. It was a 30' run from the box to the outlet. It was less than $125 for everything which included the wire, breaker, old construction box, outlet, faceplate, drill bit for running the wire through a stud, and the breaker box grommet. I got lucky with the wire because there was a 50' remnant of 6/3 Romex for half price per foot at Home Depot.
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