Is it safe to use 70 amp breakers for home wall connectors to charge Model 3?

[kakao]

I've been trying to get the home wall connector installed since late October... and it's still not done right.
Originally, the electrician used 40 amp breakers and it did not pass the inspection (I'm in Canada btw). They advised using 60 amp breakers.
However, the electrician said he doesn't have 60 amp breakers in stock due to shortage.
I patiently waited but did not get any update so I told the electrician I will have to find another electrician who has 60 amps in stock.
He then came, and installed 70 amp breakers as a 'temporary' solution. Had he told me that he was going to install 70 amps as a temporary solution, I would've told him not to bother with it and just wait for the 60 amps to arrive. Of course, the inspection hasn't been done yet because it just will not pass.

I have pretty much zero knowledge in electricity. I haven't used this home charger because of the fear of possibly damaging my car, but it really sucks I have to use superchargers everyday... Would it be safe to use this charger as long as I use my app to set a max amp output?

Thanks in advance!

 

[Solor]

The breaker is sized to protect the wires in the house/garage going to the outlet. If the wires are sized for a 40A breaker then you cannot install anything larger than a 40A breaker. If the "electrician" installed a 70A breaker then the wires had better be of the correct size otherwise it is a fire hazard.

 

[TLLMRRJ]

According to Tesla, 60amp is the max. You can go with a lower Amp breaker, but then you need to set the max Amps of the charger per this chart.

 

[marcham]

1) what gauge wiring was installed?
2) there's nothing against code to use a smaller breaker, the charger is prorammed accordingly, inspector is wrong
3) check out Canada Breakers - Buy Circuit Breakers Online
4) ditch your 2nd electrician, 1st one did it right given what's available . Shortage is real.

 

[RedModel3]

According to Tesla, 60amp is the max. You can go with a lower Amp breaker, but then you need to set the max Amps of the charger per this chart.

View attachment 742627

60 amps may appear to be the max, but that's just because the Model 3 is only capable of charging at 48 amps. When my electricians had to fix an electrical issue with the subpanel that connected my wall charger, they installed a 100 amp breaker and I've had no problems for 3 years. While I don't know Canadian electrical codes, I can't really see a reason why a 70 amp breaker should be a problem.

 

[rwiegand]

The breaker is sized to protect the wiring in the wall, period. It doesn't matter what you are plugging into it (unless the Tesla install instructions specify a breaker size, in which case they prevail), whether it's a charger or a 0.01 watt night light. If your wires are big enough you can install a 70 A breaker (or 100). If they've used the #6 copper that would be typical for a Tesla charger install then no, you can't put a 70A breaker on the circuit. If they used #4 or larger, then yes.

 

[kakao]

Thanks for the reply everyone.

1) what gauge wiring was installed?
2) there's nothing against code to use a smaller breaker, the charger is prorammed accordingly, inspector is wrong
3) check out Canada Breakers - Buy Circuit Breakers Online
4) ditch your 2nd electrician, 1st one did it right given what's available . Shortage is real.

Just to clarify it was the same electrician that installed the 70amp. This was the email I received from the electrician regarding the inspection: "I have reviewed the report from the esa inspector they have put out a bulletin to no longer accept Tesla gen 3 chargers on 40 amp because Tesla has removed dip switches infavor of software locks."
Also, I believe he used a #6 gauge wire. It was a smaller wire (#8) when he installed the 40amp breaker, but when he came to replace the breaker to 70amp, he switched the wire to a #6.
Given that he eventually replaces the breaker to 60amp, is it okay to use this wire?

 

[TLLMRRJ]

#4 gauge wire is recommended for 70 amp.

 

[Gauss Guzzler]

The wire size doesn't matter in this case - there is simply no legal/safe way to use a 70A breaker with a modern Tesla charger of any type.

It won't affect the car or charger and is generally quite safe, but the oversized breaker slightly increases the chance of fire if it fails to protect the charger or wiring in the event of a catastrophic short circuit.

I'd go ahead and use it, electrical fires are almost always caused by resistance heat at the receptacle terminals and other junctions, not by currents higher than the wire rating. And there's almost zero possibility that you would have some major overcurrent event so far beyond the 60A rating of your wiring that it poses a fire risk, yet so far below the 70A rating of your breaker that it doesn't trip.

 

[augkuo]

Basically what the Canadian code is saying is that because the gen3 charger could draw a maximum of 48A you need a breaker size of 48A + 20% margin = 57.6A or a 60A breaker with at least #6 gauge wire. If you had a 40A breaker, you would be limited to 32A charging and if somehow there was a software bug/setting which allowed the charger to draw more than 40A, then the breaker would trip stopping your charge. You already have the #6 gauge wire so that should be able to handle ~60A. So you can put the 40A breaker back in, keep the #6 gauge wire and that should pass the inspection. Keeping the 70A would mean the inspector might want you to upgrade the wiring to #4 gauge ;(

 

[Jeremy3292]

6 gauge THHN/THWN copper wire is rated for 90*C and 75 amps (not ROMEX). So in this case the wiring requirement for the 60 amp and 70 amp breaker is the same. The Model 3 will not charge faster than 48 amps as the car will not allow it (AC/DC in car converter max).

So I don't really see a *technical* issue here but not sure what local Canadian code allows.

Source for wiring temps/amps:

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

 

[Jeremy3292]

#4 gauge wire is recommended for 70 amp.

View attachment 742771

This is an NM-B wiring chart, trade name ROMEX. It is unlikely that is the wire being used for a Tesla wall connector. You would use individual THHN/THWN connectors where the ampacity is much greater.

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

 

[kakao]

Okay, so I guess I'll go ahead and use it as is for the time being? (70 amp breaker + 6 gauge wire). Hopefully my electrician gets his 60 amp breaker soon.

 

[Jeremy3292]

Okay, so I guess I'll go ahead and use it as is for the time being? (70 amp breaker + 6 gauge wire). Hopefully my electrician gets his 60 amp breaker soon.

It is a simple breaker swap once he gets the 60 amp breaker so I don't see why it is a problem to use the 70 amp breaker for now.

I would love to hear a technical answer from anyone who may be an electrician on this forum.

 

[tm1v2]

I'm no electrician, but if the circuit wiring meets 70A spec/code then you can just leave the 70A breaker in there. No need to downgrade it to 60A.

As others here stated, the breaker is there to protect the wiring of its circuit from overdraw. It should NOT be the breaker's job to protect the wall connector's internal wiring and cabling from overdraw. The wall connecter should have its own overcurrent trip protection for that. I don't actually know for sure that it does, but I would be very surprised and dismayed if it does not.

 

[brkaus]

Is the protect the wire thing true? Could you put a 100a breaker on an AC unit or electric hot water heater for example?

Regarding code and the software lock, is that actually Canadian code or the local AHJ?

Sorry for the stupid questions, just had to ask.,,

 

[tm1v2]

Is the protect the wire thing true? Could you put a 100a breaker on an AC unit or electric hot water heater for example?

I've never owned a home with AC or electric hot water, but if those plug into outlets, then the circuit breaker must match the outlet rating. When there's an outlet involved protecting the outlet is part of the circuit breaker's job.

 

[tm1v2]

I've never owned a home with AC or electric hot water, but if those plug into outlets, then the circuit breaker must match the outlet rating. When there's an outlet involved protecting the outlet is part of the circuit breaker's job.

I should mention, maybe a wall connector / EVSE could be designed where it depends on the upstream circuit breaker like the cord wiring for a dumb appliance.

However most EVSE, including all Tesla wall connector models, are configurable for different size circuits. I believe they should have their own overcurrent protection builtin that adjusts for the max configured charge rate, e.g. if you set a 48A capable wall connector to 40A max and the car then ramps past 40A, the wall connector should disconnect the car on its own, not rely on the upstream 50A breaker to trip.

At least that's my understanding. I would appreciation confirmation or correction from anyone with more knowledge on this.

 

[tm1v2]

Thinking about this more...there will be electrical wires / bars inside the EVSE upstream from its internal overcurrent protection. That wiring should be sized for the EVSE's largest supported circuit size, e.g. 48A continuous draw on a 60A circuit. Having that wiring on a 60A breaker does seem preferable to 70A.

So I take back my previous comment. Downsizing the temporary 70A breaker to 60A is probably worthwhile, in a very mild sense of worthwhile. An EVSE doesn't draw significant current on its own, and it would take all of the following together for this 60A vs 70A circuit issue to matter:

1) A car plugged into the EVSE draws more than 60A and less than 70A of current, despite the EVSE telling it max 48A.
2) EVSE overcurrent protection fails and does not trip.
3) The car does NOT draw more than 70A and avoids tripping the 70A circuit (while still drawing more than 48A).

Let's say there was a disastrous short circuit on a car charging connection...and the EVSE overcurrent protection failed...I think it would flip even the 70A breaker right quick.

I should really stop posting about this and leave it to a good electrician.

 

[Gauss Guzzler]

I'm no electrician, but if the circuit wiring meets 70A spec/code then you can just leave the 70A breaker in there. No need to downgrade it to 60A.

That's incorrect. Anything hardwired (e.g. wall connector) is considered to be a part of the circuit and the breaker must always be the weakest link in that circuit.
Anything not hardwired (e.g. mobile connector plugged into a 14-50 outlet) is not part of that circuit - it's a consumer device regulated by UL with its own safety standards so it's perfectly fine to plug a 32A charger into a 50A outlet.

IOW, you can't (legally) install a 60A wall connector on a 70A breaker for the same reason you can't install a 50A outlet on a 70A breaker.