60A Breaker Trips in Daytime Vegas Heat Only

[Cosmacelf]

The good news is that this is straightforward. Your previous electrician was a moron who violated electric code in a pretty basic way. There's nothing wrong with using NM-B, but it is necessary to use the right gauge of wire. 6 gauge NM-B simply does not meet the rating for a 60A circuit. Period. So this is correct, that if it's going to use NM-B, it should have been 4 gauge.

You can just change this to a 50A circuit, drawing 40A continuous, and it should be fine.

Yeah, that’s the cheapest option, just buy a 50A breaker, change the setting in the Wall Connector and be done with it.

 

[DownshiftDre]

Probably because he didn't want to cut the drywall to run it through the studs and didn't have THHN in the truck...or he's an idiot. Of course, those two choices are not mutually exclusive. If the new electrician is going to change it over to THHN, he could use 6AWG, but if he's willing to use 4AWG and wrestle it into the wall connector, that's great.

That said, I don't think the wire choice explains the tripping breaker. I have to think the OP either got a dud of breaker, or the connections at the breaker were not tight enough. Given the quality of the work, I'd wonder whether the guy just chucked some used breaker he happened to have in the truck in there.

Yes he said his wire is 4AWG individual, not bundled. Looking online sounds like THHN . Funny he did mention he will have to wrestle it into the wall connector where it does the 180 bend and said its not easy to bend.

 

[lencap]

I'm facing similar wiring challenges with my newly installed Wall Connector. One thing that may be an issue is that there appears to be a temperature sensor inside the Tesla Wall Connector, according to the Installation manual. I've attached the image - page 15, Gen 3 Wall Connector Manual. The point is that whatever you do to improve your service, if ambient temperature is high, and if the Wall Connector generates heat while charging, maybe you should ask the electrician if you may still have issues with the new install.

I decided to keep my current NM-B #6 gauge wiring and downsize the circuit breaker to 50amps to avoid having to rewire the Wall Connector. It's still faster than the 40amp circuit I'm currently using, and fully meets code with a 50amp breaker and no wiring change.

 

[Sophias_dad]

I'm facing similar wiring challenges with my newly installed Wall Connector. One thing that may be an issue is that there appears to be a temperature sensor inside the Tesla Wall Connector, according to the Installation manual. I've attached the image - page 15, Gen 3 Wall Connector Manual. The point is that whatever you do to improve your service, if ambient temperature is high, and if the Wall Connector generates heat while charging, maybe you should ask the electrician if you may still have issues with the new install.

I decided to keep my current NM-B #6 gauge wiring and downsize the circuit breaker to 50amps to avoid having to rewire the Wall Connector. It's still faster than the 40amp circuit I'm currently using, and fully meets code with a 50amp breaker and no wiring change.

There is indeed a temperature sensor in the wall connector, looking specifically at the input lugs to see if they are overheating. From what I can tell, the sensor needs to read somewhere north of 180f before it even thinks about rolling back the power, and even then it isn't a sharp cutoff. There were a zillion Gen3 HPWCs(mostly model numbers ending with -F) made with defective relays that would overheat horrendously.

 

[DownshiftDre]

I'm facing similar wiring challenges with my newly installed Wall Connector. One thing that may be an issue is that there appears to be a temperature sensor inside the Tesla Wall Connector, according to the Installation manual. I've attached the image - page 15, Gen 3 Wall Connector Manual. The point is that whatever you do to improve your service, if ambient temperature is high, and if the Wall Connector generates heat while charging, maybe you should ask the electrician if you may still have issues with the new install.

I decided to keep my current NM-B #6 gauge wiring and downsize the circuit breaker to 50amps to avoid having to rewire the Wall Connector. It's still faster than the 40amp circuit I'm currently using, and fully meets code with a 50amp breaker and no wiring change.

I will not be surprised if I have a similar experience with tripping breaker in the deep summer at sustained 48A max. The ambient summer heat is extreme and with an external electrical panel, the margin goes down further. I was debating going the 50A breaker route as he mentioned that option but I then I would still have the “code violations” so figured lets get it all up to snuff and deal with any remaining after effects as they come. Daytime charging is a rarity for me and dialing down a few amps will barely make a difference in speed.

With things slowly starting to cool down and more travel coming up for me, I probably wont be able to fully stress test the system until next summer. We have two Teslas and the morning scheduled charging/departure routine at 48A works fine.

 

[DownshiftDre]

There is indeed a temperature sensor in the wall connector, looking specifically at the input lugs to see if they are overheating. From what I can tell, the sensor needs to read somewhere north of 180f before it even thinks about rolling back the power, and even then it isn't a sharp cutoff. There were a zillion Gen3 HPWCs(mostly model numbers ending with -F) made with defective relays that would overheat horrendously.

Good point. I have a -G which supposedly corrected this. Did have Tesla monitor the unit while I was charging and while it tripped and they found no issue on their end.

 

[mongo]

Good point. I have a -G which supposedly corrected this. Did have Tesla monitor the unit while I was charging and while it tripped and they found no issue on their end.

Makes sense. If the breaker is tripping due to its temperature, WC temp and current would be normal up until it loses power.

 

[Sophias_dad]

Good point. I have a -G which supposedly corrected this. Did have Tesla monitor the unit while I was charging and while it tripped and they found no issue on their end.

I was not trying to indicate your problem is HPWC overheating, but rather I was just giving some additional information about the temperature sensor.

Just as a datapoint, it might be helpful for you to use the tewamo app to check the temperature sensor value after 40 minutes of 48 amp charging, to get a sort of 'known to be okay' temperature.

 

[DownshiftDre]

I was not trying to indicate your problem is HPWC overheating, but rather I was just giving some additional information about the temperature sensor.

Just as a datapoint, it might be helpful for you to use the tewamo app to check the temperature sensor value after 40 minutes of 48 amp charging, to get a sort of 'known to be okay' temperature.

Interesting. Did not know of that app and I like getting my hands on any data I can. Thanks.

 

[Cosmacelf]

I will not be surprised if I have a similar experience with tripping breaker in the deep summer at sustained 48A max. The ambient summer heat is extreme and with an external electrical panel, the margin goes down further. I was debating going the 50A breaker route as he mentioned that option but I then I would still have the “code violations” so figured lets get it all up to snuff and deal with any remaining after effects as they come. Daytime charging is a rarity for me and dialing down a few amps will barely make a difference in speed.

What code violations would you still have? Popping in a 50A breaker should fix everything in that regard.

 

[mongo]

Technically, wouldn't setting the WC to 40A charge do that also? 60 Amp upsized breaker on 55Amp wire for a 40Amp load.

 

[davewill]

Technically, wouldn't setting the WC to 40A charge do that also? 60 Amp upsized breaker on 55Amp wire for a 40Amp load.

It would, however, we know that that breaker is tripping when it shouldn't be, so it needs replacing anyway. Might as well use a 50a.

 

[DownshiftDre]

What code violations would you still have? Popping in a 50A breaker should fix everything in that regard.

True. I guess I was thinking of the wire in the plastic conduit. Maybe my words of code violations was more meant to say bad practices.

 

[stopcrazypp]

True. I guess I was thinking of the wire in the plastic conduit. Maybe my words of code violations was more meant to say bad practices.

NM-B is allowed and in fact required under code to be run in conduit for protection when exposed (not inside a wall).

Can Romex (NM-B) cable be run through conduit?

A few days ago I asked an electrician if I could run cable through conduit - he gave me a funny look and said "No, Romex is not allowed in conduit." When I searched online, there seems to...

diy.stackexchange.com

The problem with your installation is that is undersized/overloaded, and the plastic conduit just makes it worse in terms of overheating. It's a fairly common mistake given the rating at 55A is just barely under the 60A asked for.

 

[mongo]

NM-B is allowed and in fact required under code to be run in conduit for protection when exposed (not inside a wall).

Can Romex (NM-B) cable be run through conduit?

A few days ago I asked an electrician if I could run cable through conduit - he gave me a funny look and said "No, Romex is not allowed in conduit." When I searched online, there seems to...

diy.stackexchange.com

The problem with your installation is that is undersized/overloaded, and the plastic conduit just makes it worse in terms of overheating. It's a fairly common mistake given the rating at 55A is just barely under the 60A asked for.

The wire in the conduit is not overheating the breaker.
Nothing is asking for 60, the EVSE is set to 48A. Continuous loads are defined as > 3 hours, the breaker trips in less than one.
The problem is the panel is hot (with AirCon breakers not helping) and/or the breaker is weak.

 

[DownshiftDre]

Electrician coming today (ahead of weekends remnant rains from Hurricane Hilary). May get a final chance at a stress test soon early next week as temps hover right around 100 but start to drop.

 

[stopcrazypp]

The wire in the conduit is not overheating the breaker.

Tests have not been done with different conductors yet to establish that. Heat can conduct through wires.

Nothing is asking for 60, the EVSE is set to 48A.

I'm talking about the wire rating the EVSE asks for obviously.

Continuous loads are defined as > 3 hours, the breaker trips in less than one.
The problem is the panel is hot (with AirCon breakers not helping) and/or the breaker is weak.

The wire is undersized so it becomes ambiguous at which point the trip point may be.

 

[mongo]

Tests have not been done with different conductors yet to establish that. Heat can conduct through wires.

The lead in to the breaker is unsheathed and won't conduct much/ any of the heat from the conduit enclosed section. So the heat generated at the breaker is basically the same for NM-B or THHN (especially since NM-B is often made with THHN wire).

The wire is undersized so it becomes ambiguous at which point the trip point may be.

Wire size is irrelevant to breaker trip point. The breaker only monitors current. A motor load might pull more current due to voltage drop, but a current controlled EV charger won't. The power delivered will be less, but the current won't exceed the setpoint. 48A shouldn't trip a 60A breaker, regardless of duration.

If the car were faulting on voltage drop, that would be a wire effect.

 

[stopcrazypp]

The lead in to the breaker is unsheathed and won't conduct much/ any of the heat from the conduit enclosed section. So the heat generated at the breaker is basically the same for NM-B or THHN (especially since NM-B is often made with THHN wire).



Wire size is irrelevant to breaker trip point. The breaker only monitors current. A motor load might pull more current due to voltage drop, but a current controlled EV charger won't. The power delivered will be less, but the current won't exceed the setpoint. 48A shouldn't trip a 60A breaker, regardless of duration.

If the car were faulting on voltage drop, that would be a wire effect.

Others pointed out breakers trip at different currents depending on the temperature. So the wire size would play a factor in this case if it is generating heat. So while it's true that the breaker shouldn't trip if everything was done to spec, it wasn't, so that expectation kind of goes out the window. It could be just at the borderline, which is why it only happens during the day when temps are high.

 

[mongo]

Others pointed out breakers trip at different currents depending on the temperature. So the wire size would play a factor in this case if it is generating heat. So while it's true that the breaker shouldn't trip if everything was done to spec, it wasn't, so that expectation kind of goes out the window. It could be just at the borderline, which is why it only happens during the day when temps are high.

Sure, but if NM-B uses THHN internally, and NM-B sheath must be removed when entering the panel, and there is at least 12 inches of free wire, and the wire runs through a wall before entering the conduit, how much impact will that conduit have on the breaker temperature?
#6 copper wire has a crossection of 13.3 mm^2, copper has a thermal conductivity of 398 W/mK, a 300mm long piece conducts 398 * (13.3/300/1000) = 28mW per degree Kelvin or Celsius temperature differential. Two wires to the breaker so 56mW/K, and that's assuming the wire in the wall is warmer than the panel and no convective cooling.
Self heating in the panel: 6 AWG copper resistance is 1.3 mOhm per meter. 300mm at 48 Amp = .39mOhm * 48 * 48 = 900mW each conductor.