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!

 

[tm1v2]

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.

I now think most of what you said above is correct, except - it's only fine to plug a 32A charger into a 50A outlet if the charger has its own cable/plug/adapter for that. If your portable charger has a 30A plug (for 24A charging), I'm pretty sure it's not really okay to use a dumb adapter with no internal overcurrent protection to plug that into a 50A outlet. The 30A plug on the portable charger isn't rated for a 50A circuit.

Yes I'm aware using plug adapters (separate from the portable charger's own plug set) is not unheard of among EV owners when in a pinch with limited charging options. I would certainly do it once if needed to not be stranded somewhere (being careful to set the car's max charging amps appropriately). But I would never repeatedly/regularly use such a setup.

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.

I think I've come to that same conclusion now, see above.

 

[a64pilot]

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.

No, that’s incorrect.
Think of it this way, a regular wall circuit is either 15 or 20 amp, and you can install a door bell on one or an alarm system, sprinkler systems and or dozens of other things that don’t even come close to the circuits rating. There is NO safety issue with an item that's rated at less then the circuit capacity
So it’s perfectly acceptable to use less than a circuits rated capacity, but not more, in fact it’s almost always the case.

Again look at it this way, it’s normal for a wall circuit to cover a half dozen receptacles, and it’s entirely possible to plug in a stationary heater into everyone of those receptacles. which obviously seriously exceeds the circuits capacity. but as the wires capacity exceeds the rating, all that happens is that the CB opens.

However as was stated previously if you involve a plug or receptacle,it’s part of the circuit wiring and in that case you can’t put a 50 amp plug on a 70 amp circuit. If for example you put a 15 amp plug on, then it becomes a 15 amp circuit. The plug is considered part of the wiring

 

[a64pilot]

MY SR+ can only draw 32 amps from my WC, and therefore only requires a 40 amp breaker, but I installed it with a 60 amp breaker and thats perfectly fine.
I could also have used a 70 amp or even a 100 amp breaker as long as the wiring would support it.

People get confused as they think the CB is to protect the attached component and that is NEVER the case, the CB is sized for the wire, and the wire is sized for the load, and it’s perfectly acceptable and in fact usually desirable for the wire to be one size larger than min required, just gives a little extra safety margin. Contractors only wire to min specs to save a little money, so houses get wired to min specs.

 

[rpiotro]

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 ;(

In the US the code is for +25%. 48 amp continuous load would require 60 amp. 32 amp would require 40 and so on.

 

[Gauss Guzzler]

It doesn't matter how much power your doorbell uses @a64pilot, what matters is that it is intended to safely withstand up to 20A in the event of a short circuit. That's why the instructions say it must be installed on a 15-20A circuit. It would not be safe on a 30A circuit because it is reliant on the breaker to prevent it from starting a fire.

Likewise with a wall charger. It's intended to handle a 60A short without catching fire. If you ignore the instructions (and therefore the law) by putting it on a 100A breaker then in the event of a failure you could have a lot more power and heat flowing thru it before the breaker trips, and thus a greater risk of fire.

But a 32A portable charger on a 50A circuit is fine because the charger was designed to be safe in the event of a 50A short, as evidenced by the fact that it is UL listed with it's 50A plug adapter.

 

[Jeremy3292]

It doesn't matter how much power your doorbell uses @a64pilot, what matters is that it is intended to safely withstand up to 20A in the event of a short circuit. That's why the instructions say it must be installed on a 15-20A circuit. It would not be safe on a 30A circuit because it is reliant on the breaker to prevent it from starting a fire.

Likewise with a wall charger. It's intended to handle a 60A short without catching fire. If you ignore the instructions (and therefore the law) by putting it on a 100A breaker then in the event of a failure you could have a lot more power and heat flowing thru it before the breaker trips, and thus a greater risk of fire.

But a 32A portable charger on a 50A circuit is fine because the charger was designed to be safe in the event of a 50A short, as evidenced by the fact that it is UL listed with it's 50A plug adapter.

So TLDR is basically what is the path of least resistance. The Tesla Wall Connector is only rated to withstand 60 amps, regardless of how good your wiring is.

 

[Gauss Guzzler]

Or more generally, that the breaker must be limited by the lowest rated hardwired component in the circuit.

Beyond the outlet it's UL's problem. But if there isn't an outlet, then it falls under the above NEC/CEC rule whether it's lighting, EVSE, HVAC, or a doorbell.

 

[Outpost53]

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

You can only use the 90c column if both ends of the termination are rated for 90c and neither the breaker or the wall charger are so you can't use the 90c column.

 

[Lanzer]

Technically speaking your Model 3 won't draw enough power to strain a 6 gauge cable, so you should be fine.

Having said that, the point of having a breaker is for unforseen circumstances such as some freak of nature short circuit situation (someone cutting the cable accidentally, water damage, etc), and you will want the breaker to trip before the wire melts and start a fire. Technically speaking a 60amp breaker will prevent heat build up better than the 70amp breaker for a 6 gauge wire, that's why only a 60 amp breaker will pass inspection. Also note that in the unlikely case that a fire is started, insurance won't cover you if the breaker is not up to code. Highly unlikely scenario but better to know ahead of time.

 

[Lanzer]

Upon reading the rest of the thread I noticed that some people are using the amperage in outlet, circuit, and breaker interchangeably, and also having incorrect conception on how to choose the right sized circuit breaker. I then realized that this forum is a terrible place to be asking questions about wiring. We share our love in Tesla, but I don't think we share any electrician license.

There are forums such as (InterNACHI Forum) who have more professionals that can answer these questions with authority.

 

[JayNJ]

Putting the 40A breaker would have been better and to code. Yes it would trip sooner than a 60A if there is an issue with the SW on the EVSE, but from a safety standpoint that is ok.

 

[stopcrazypp]

Or more generally, that the breaker must be limited by the lowest rated hardwired component in the circuit.

Beyond the outlet it's UL's problem. But if there isn't an outlet, then it falls under the above NEC/CEC rule whether it's lighting, EVSE, HVAC, or a doorbell.

I guess it depends on Canada's electrical code. But at least for California (and generally USA) you are right, the device rating matters too (especially when it's permanently installed like an EVSE).

Relevant section here:

210.20 Overcurrent Protection

Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).

(A) Continuous and Noncontinuous Loads

Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.
Exception: Where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

(B) Conductor Protection

Conductors shall be protected in accordance with 240.4. Flexible cords and fixture wires shall be protected in accordance with 240.5.

(C) Equipment

The rating or setting of the overcurrent protective device shall not exceed that specified in the applicable articles referenced in Table 240.3 for equipment.

(D) Outlet Devices

The rating or setting shall not exceed that specified in 210.21 for outlet devices.

https://up.codes/viewer/california/ca-electric-code-2019/chapter/2/wiring-and-protection#210.20_(C)

Basically part C covers what you mentioned. An example in that 240.3 table is a common surface element stove, you can't use a overcurrent protection device rated more than 50A regardless of the ampacity of the wiring you installed.
https://up.codes/viewer/california/...hapter/4/equipment-for-general-use#422.11_(B)

They don't have specific ratings/instructions for EVSEs yet in that table, but if you look up an inspector checklist for EVSEs (here's one for San Luis Obispo, just the first result I found):

7. Verify the size of the branch circuit overcurrent protection is per nameplate and protects the conductors. NEC 110.3(B), 240.4

https://www.slocounty.ca.gov/Depart...11082019-Electric-Vehicle-Supply-Equipmen.pdf
240.4 covers the conductors, but 110.3(B) is the part that covers the EVSE:

110.3(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

NEC 110.3(B) and The Intermixing of Circuit breakers.
Tesla's instructions call for a 60A breaker for the Gen 3 Wall Connector when your max output is 48A (page 5). It does not say you can use a larger breaker. So the inspector can fail you based on using a breaker larger than specified in instructions.
https://www.tesla.com/sites/default...ng/Gen3_WallConnector_Installation_Manual.pdf

Of course for the OP, it really depends on Ontario's local codes, but likely the logic would be the same.

 

[Jeremy3292]

You can only use the 90c column if both ends of the termination are rated for 90c and neither the breaker or the wall charger are so you can't use the 90c column.

No, the columns tell you the ampacity of the gauge and type of wire that is being used. It has nothing to do with anything else. ROMEX is rated at less ampacity and temperature than THHN wire as it is sheathed overall with other wires. The chart literally lists the different types of wire and their respective ampacity and temperature ratings.

The Wall Connector manual says to use minimum 6 gauge, 90 C copper connectors if installing for maximum power. That would be 6 gauge THHN wire which is rated for a maximum of 75 amps and 90 C. 6 gauge ROMEX or NM-B wire is rated at a maximum of 55 amps and 60 C, which would not be suitable for a Wall Connector. Neither is 4 gauge ROMEX as it is rated to 60 C which violates Tesla’s manual.

The breaker amperage is an entirely separate discussion.

 

[Outpost53]

No, the columns tell you the ampacity of the gauge and type of wire that is being used. It has nothing to do with anything else. ROMEX is rated at less ampacity and temperature than THHN wire as it is sheathed overall with other wires. The chart literally lists the different types of wire and their respective ampacity and temperature ratings.

The Wall Connector manual says to use minimum 6 gauge, 90 C copper connectors if installing for maximum power. That would be 6 gauge THHN wire which is rated for a maximum of 75 amps and 90 C. 6 gauge ROMEX or NM-B wire is rated at a maximum of 55 amps and 60 C, which would not be suitable for a Wall Connector. Neither is 4 gauge ROMEX as it is rated to 60 C which violates Tesla’s manual.

The breaker amperage is an entirely separate discussion.

1) It doesn't matter what the temperature of the wire is if the termination points are rated less and there are no 90c rated breakers so you have to use 75c. There are, however, 90c rated lugs. You can use the 90c column for purposes of derating and conduit fill but not wire ampacity. The NEC says you have to use the 75c column for thhn, thwn, etc for wire ampacity so it is rated for 65 amps.

2) You still can put a 70 amp breaker on #6 provided that there are no more than 3 current carrying conductors in the conduit and you don't have to derate since a #6 wire is good for 65 amps in a branch circuit and there are no 65 amp breakers so you are allowed to bump up to the next commonly available size. Unless your load is a motor and then things change a lot.

3) like you said, the manual says #6 or greater on a 60 amp breaker so the manual wins. Doesn't matter what the NEC says.

This, of coarse, is all according to the NEC and the op is in canada so while usually very similar they do have some different rules up there.