40A Breakers Get Hot When Charging

[Bikeman]

Six years ago an electrician installed a couple new circuits on our breaker box. One was a 40A 240v specifically for charging a car. The other was a 20A 120v circuit as a backup charging circuit. The 240 ends in a 14-50 outlet in which a JuiceBox40, of similar age, has been used. When my wife charges her car, it is limited to 12A 240v, and the breakers get warm to the touch after 15 minutes. When I charge my Y at 31A 240v, the breakers in the panel get beyond warm -- I might say they get hot. We have a suspicion that the breaker has tripped at least once while charging the Y, as charging output slowed down to a crawl. It hasn't since, but the breakers are always warm/hot when in use.

We have tried charging with the Tesla Mobile connector as well, at 32A 240v, and breakers also get pretty hot. So I can rule out both cars and probably both EVSE's as a cause.

The breaker box is a decades-old GE 100A, and the breakers are 6 year-old GE brand. I think I remember that the electrician said he had to match brands so they would fit in the breaker box. The run to the 14-50 outlet is about 12 to 15 feet. I don't know if the wiring is 6 or 8 gauge.

So, what should we be looking to do? Do your breakers get warm or hot when at 80% load? Have you ever checked them well into a charging cycle? I can guess it might be a connection of the breakers into the panel bus? Could be crappy breakers? Or a wire loosening on the breaker? Or maybe the wiring is sub-par for a 40A 14-50 useage? What should we be asking an electrician to check, or maybe replace?

In the mean time, we've been charging the Prius Prime at its full charging spec which is 12A 240. I have limited my Tesla charging down to 20A and they get less hot, but the situation is still troubling me. We have also used the 20A 120v circuit as our other portable EVSE's are limited to 12A 120v and that in no way makes the breaker warm. Even with another 120v circuit which is a 15A (standard), that breaker is cool to the touch when charging to 80% of that circuit capacity.

Breakers:

Charging area outside, under the covered porch:

 

[Cnixon]

Nothing should get hot! I would hope its just a bad screwed connection (over tightning can be as bad as under tightning!). Other than that there is no harm in changing the 240v breaker (pair) if they are still available. I am in uk so unsure about your 'gauge' wiring. But here I would be using minimum 10mm2 cable for that run. If cable was problem it would all get hot so you are looking at the right end! If you have stranded cables electrician should crimp together for best current carrying capacity.

 

[dafish]

Well…

let’s get some data on warm and not. buy or borrow an ir temp gun maybe?

breakers can, and are expected to, get warm to hot. 60c is the low end of rated operational temp, 75c rated breakers are common enough

prolly a good idea to check the receptacle and the breaker, make sure the wire connections are tight. Arcing makes a lot of heat..

if really concerned you should add “find out for sure what wire gauge you are using.” to the list

 

[henderrj]

I'm also amazed it's not a 50 amp breaker. That's a nema 14-50, as in 50 amps. I think you're doing right in simply reducing the amperage. Breakers will get warm, but they shouldn't be exceedingly warm. It could be wearing out, as the poster above said it could be a bad connection. I would have someone who knows what they're doing check it. And again agreeing with what has already been said, probably just go ahead and replace the breaker. They're around 20 bucks.

 

[RandyS]

Also check your car's screen to see what the voltage is right when the charging session starts and what the voltage drops to when the full rated charging current is flowing...Hopefully it's not more than a couple of volts. If it's more, then that would point to a poor connection...If the connections appear tight, you could also remove the breaker from the panel and re-insert it to make sure it is seated firmly on the bus...

 

[Sophias_dad]

The breaker and wire SHOULD have been rated at 50A for the Juicebox 40. As it stands, that breaker is right at its limit of tripping. EV circuits are supposed to be oversized by 25% compared to the current delivered.

Consider getting the wire and breaker upsized as necessary to carry the 50A(really 40A continuous) load and your problem will probably go away. If you want to stick with what you have, get the juicebox dialed down to 32A continuous as a maximum delivered current and get the breaker replaced. It should be a GFCI breaker(if it were a new install), maybe since its a replacement you can stick with not-GFCI.

 

[davewill]

I'm pretty sure the JuiceBox40 can be configured for a 40a circuit so it only allows 32a charging. I'm hoping that's what the OP has done. If so, then the install sounds just fine.

 

[fiehlsport]

Yes, as long as it's wired with #8 Romex or #10/#8 THHN the install is correct for a 40A breaker, if the Juicebox is pulling 32A. It is permissible to use a 40A breaker with a 14-50 receptacle, believe it or not. Would I do it? No - probably no reason to cheap out on the wire and breaker for such a thing, but it's allowed.

The problem lies in if the Juicebox is pulling 32 amps or 40. I suspect it's pulling 40 - (why else would they call it a Juicebox 40) Are you manually de-rating the current in your Tesla, and does it say 32/40A when plugged in? What's the car think the Juicebox is capable of?

In that case, the electrician undersized your circuit and you need it upgraded with the correct conductors for a 50 amp breaker. A 50A circuit allows 40A charging. A 40A circuit allows 32A charging. 80% rule with continuous loads.

 

[EdJack]

If the breaker is warm, the first thing I would check is that the wires going into the breaker are properly torqued.

* Throw main 100 amp breaker to power off the breaker box.
* Remove the Panel Cover.
* Inspect the wires in the Breaker, see if they have corrosion or burnt/blackened end.
* Tighten to correct torque. It is a process; tighten, then jiggle/pull wires, tighten again, then jiggle/pull wires, tighten again. Need to do that 3-4 times, tighten/jiggle/pull. Torque specs. are printed on the Breaker.
* If the wires had corrosion or burnt ends. Then clip off the ends to get fresh copper ends.
* Maybe even change the breaker. Maybe parts inside are arching/loose/worn out.

First thing to look for in overheating is loose wires, or other loose parts, that are arching and causing heat. Also good to check the wires going into the breaker right away, because the overheating could be causing the ends of wire insulation to start melting/burning.

How comfortable are you with working with a panel? I'd at least throw the main breaker, pull the Panel Cover off, and look at the wires. If they are starting to melt/burn, then immediately stop using the charger until an Electrician can come out. Melting wire insulation could become a fire hazard.

 

[MY-Y]

My breaker is definitely warm, quite warm, when charging for a while. This is true for all three EV circuits I have. At 48 amps, the cord and plug on my Tesla HPWC get very warm as well. Totally normal. Here's an image from my thermal camera showing a 141 degree cord on my HPWC cord. And another when it was starting to heat up.

I do think it's a good idea to check the torque on high current connections after they've had a few thermal cycles. When the connection is good, it'll still heat up though.

 

[Bikeman]

I'm pretty sure the JuiceBox40 can be configured for a 40a circuit so it only allows 32a charging. I'm hoping that's what the OP has done. If so, then the install sounds just fine.

That's exactly what I've done. Even more, this is a JuiceBox model that had the trim setting inside, and it is set for 31A max output. 32 was cutting it too close for a 40A circuit. The Tesla Mobile Charger kit, when used with the 14-50 plugset, can ONLY output 32A. There is no danger that a 40A breaker can be overwhelmed, unless there is a physical defect, which it looks as if what is happening.

Wires were fine, and cool. Charged last night setting the app to 20A. Old breaker got warm, but not hot.

 

[Bikeman]

Electrician came out yesterday. As I mentioned above, the old GE breaker is the main suspect. When it was yanked out of the panel, the contact trail on the bus was a teeny tiny scratch. There was hardly any contact. We're trying a Siemens 40A breaker in its place. Seems to have a longer contact with the bus.

The wire was/is 8 gauge, which is correct for a 40A circuit. JuiceBox can only go up to 31A, as it is manually set to that inside the unit on the trimmer. The electrician's meter showed 31.6 amps coming off the breaker when charging for 20 minutes at the full 31A output (which is why I set it to 31 and not 32). I can't make the Tesla take more than that in the settings either on the screen or in the app. Max. shows as 31/31 on both. This is where we want it, and no higher. One thing we noticed when old breaker was put back in was it didn't get as hot as a few days ago. Perhaps doing that cleaned the contact area a small bit? Dunno.

He told me that the wires were properly tightened and not too tight or too lose. We reinstalled them onto the breaker anyway. For now I'm limiting charging to 20A/230-240v (ComEd voltage varies). A Siemens breaker has considerably more contact area on the bus. One of those was picked up yesterday, and will be swapped out next time he swings by. If that doesn't do the trick, then I'd be surprised.

Ss let me back up with this... In the many years we've been charging our cars with this circuit and the JuiceBox, or with the other more portable EVSE cords we got with our cars and sometimes also use (240v and 120v), I've never actually touched any of the breakers to test for warmth until this last week. It could be that this thing has been getting warm/hot all along and has gone completely unnoticed.

 

[Bikeman]

My breaker is definitely warm, quite warm, when charging for a while. This is true for all three EV circuits I have. At 48 amps, the cord and plug on my Tesla HPWC get very warm as well. Totally normal. Here's an image from my thermal camera showing a 141 degree cord on my HPWC cord. And another when it was starting to heat up.

This is helpful. I'm assuming you're at 48A on a 60A circuit(s)?

I do think it's a good idea to check the torque on high current connections after they've had a few thermal cycles. When the connection is good, it'll still heat up though.

Agree about checking connections. We did that today and they seemed to have been originally tightened properly. If the new Siemens breaker still gets hot at 31 or 32A output, then 6g wires will be installed to rule out any possible wiring resistance issues, even though the run is under twelve feet to the 14-50 outlet. The 8g wires weren't hot at the breaker when in use today, so this isn't really suspect at this time. If the new breaker gets noticably less hot, then we'll probably just call it a day and live with the situation, and I'll likely just throttle down to something less than 31A.

 

[GData]

Ss let me back up with this... In the many years we've been charging our cars with this circuit and the JuiceBox, or with the other more portable EVSE cords we got with our cars and sometimes also use (240v and 120v), I've never actually touched any of the breakers to test for warmth until this last week. It could be that this thing has been getting warm/hot all along and has gone completely unnoticed.

It's also possible that years of expansion/contracting caused the circuit breaker to loosen from the bus bar, which would make the breaker run hot. I limit my charging to 24A to minimize the expansion/contracting cycle, and never charge while using any large appliance. I considered limiting to <20A but people said that's too inefficient because of charging overhead. At 24A, my breaker isn't even warm to the touch (I know, that's not scientific)

 

[retbesla]

I also own JuiceBox 40 since 2017, and I have the NEMA 14-50 along with 2-poles 50A breaker in place. #6AWG. I configure to run with 36A and 208V. There are 3 locations with the higher than normal temperature after I start charging for an hour. The NEMA 14-50 receptacle, the conduit nearby, and the JuiceBox input cable nearby will all be extremely warm. (I don’t have the infrared thermometer temperature gun, so won’t be able to tell the true temperature. It is the temperature similar to the bottom of my WiFi Eero 6+, it is not hot but you might not feel comfortable if holding long in summer, however, you might feel okay in winter.) The temperature is pretty stable all the way until my charging session is done.

 

[Bikeman]

^ 36A on a 50A circuit gets hot? So I'm not alone. That's only 72% of realistic capacity, and you're using 6g. Hmmmm. Have you amp'd the JB40 down to 36 because of feared overload or temperatures? You didn't mention if the 50A breaker itself gets hot. Does it?

 

[davewill]

I also own JuiceBox 40 since 2017, and I have the NEMA 14-50 along with 2-poles 50A breaker in place. #6AWG. I configure to run with 36A and 208V. There are 3 locations with the higher than normal temperature after I start charging for an hour. The NEMA 14-50 receptacle, the conduit nearby, and the JuiceBox input cable nearby will all be extremely warm. (I don’t have the infrared thermometer temperature gun, so won’t be able to tell the true temperature. It is the temperature similar to the bottom of my WiFi Eero 6+, it is not hot but you might not feel comfortable if holding long in summer, however, you might feel okay in winter.) The temperature is pretty stable all the way until my charging session is done.

If you have the Leviton 14-50 outlet, it's a likely source for the symptoms you're describing. The contacts that grip the blades of the plug, and the screws that clamp the wires are just not designed well. There's a monster thread sticky here on which outlets to choose:

Master Thread: Definitive 14-50 NEMA Outlet Guide

Comparing the 2 outlets recommended by Tesla with the sub $10 big box model as well as the one I think you should buy 1. Hubbell 9450a 2. Bryant 9450fr 3. Cooper 5754n 4. Leviton 279-S00 The Hubbell and Bryant are far and away the superior product here and since Hubbell owns Bryant and these...

teslamotorsclub.com

 

[retbesla]

^ 36A on a 50A circuit gets hot? So I'm not alone. That's only 72% of realistic capacity, and you're using 6g. Hmmmm. Have you amp'd the JB40 down to 36 because of feared overload or temperatures? You didn't mention if the 50A breaker itself gets hot. Does it?

I won’t say it is “hot” and I think I can touch or hold those areas for a long time. I know my body/hands will feel hot and can’t touch/hold bath water anymore if the water temperature is over 105-110 °F. So I “guess” the temperature is around or below that mark. (Forgive my theory. I should buy air temperature gun next time…)

I set to 36A is only because I never run things with 100% capacity, except a few things like the computer CPU. I’ll change and try 40A in my charge later tonight.

My 50A breaker is only slightly warm, just like any other high amp breakers in my household. It seems normal to me. I’ll check it again tonight.

The pics below are my JuiceBox40. (I got the original one in the end of 2017, and had the multiple defects. This box in the pic is the 4th JuiceBox40 I received and has been working great since 2019).

I have 7’ long conduit from the breaker to 14-50. The 1st pic shows how they look like in the end of 14-50. And in the 2nd pic, I highlighted those I feel extremely warm. Other areas are just slight warm or almost nothing.

 

[retbesla]

If you have the Leviton 14-50 outlet, it's a likely source for the symptoms you're describing. The contacts that grip the blades of the plug, and the screws that clamp the wires are just not designed well. There's a monster thread sticky here on which outlets to choose:

Master Thread: Definitive 14-50 NEMA Outlet Guide

Comparing the 2 outlets recommended by Tesla with the sub $10 big box model as well as the one I think you should buy 1. Hubbell 9450a 2. Bryant 9450fr 3. Cooper 5754n 4. Leviton 279-S00 The Hubbell and Bryant are far and away the superior product here and since Hubbell owns Bryant and these...

teslamotorsclub.com

Can’t remember the brand. No physical sign or logo shows the original manufacturer. Maybe I’ll need to open it up in order to see it.

I heard Leviton’s issue before but never read the details about it. Will try to understand it then. Thanks for sharing.

 

[retbesla]

Well. Tried to use 40A last night in my JuiceBox 40. The 14-50 receptacle and nearby were getting hot, which becomes something I don’t want to touch. The breaker remain slightly warm. Thanks @davewill suggested that Leviton is the possible culprit. I shut off the power and opened it up. It is Leviton. I also found that one of the legs/holes is slightly burned. I’m asking the technician to check and get me something like Hubbell or Bryant. Also thanks @Bikeman for having this thread.