Model 3 Tripping 50amp breaker @ 40amp charging

[SageBrush]

Sure.... but the charger is able to pull 48A. I'm not an electrical engineer but I would think it might be possible something isn't calibrated correctly and the car is either misinterpreting a 40A pilot signal as >40A or the car thinks it's pulling 40A when it's really pulling >40A.

Agreed,
My point was that if > 40 A is going into the battery the SoC may show greater than 11% an hour rise

 

[nwdiver]

Yep,
My point was that if > 40 A is going into the battery the SoC may show greater than 11% an hour rise

Ah... I get it... makes sense. That's a good idea....

 

[DrDabbles]

The car SHOULD detect and prevent this. I know my car has slowed / stopped charging because of a voltage drop... I hope this become a NFPA requirement for EVs.

Agreed. But I think I watched a Ben Sullins video the other day where he tried to do 120v charging for a week, and his car complained that the charger wasn't performing properly, but continued with charging. Then the breaker tripped several hours later. I assume that was a voltage drop issue, since a nearby outlet worked fine.

Anyway, getting some NFPA regulations would be good. The NEC already contains lots of good notes and a section for EV charging, but I think the next version needs to contain info for residential high power A/C charging.

 

[nwdiver]

his car complained that the charger wasn't performing properly, but continued with charging.

At the same amperage?

 

[MikeQ]

I think I found my problem. The X has been charging fine until last night. It tripped the breaker too.

I opened the HPWC and tightened the connectors from the charging cable. They didn't really seem loose but gave them a little nudge. Then I opened the panel with the 50amp breaker and could see the legs coming out of the breaker to the HPWC had a clear plastic coating over the white/red coating. The clear coating was cracked and pulling away from the wire. I could tell this was heat damage. Checked the screw terminals on the breaker and load wire was really loose. I could have pulled free from the breaker. Tightened it down and so far so good.

I think the breaker tripping on the Model 3 was just unfortunately the first time we've seen this so it seemed like it was a Model 3 problem.

 

[NickFie]

If you can safely do so, turn off power to sub-panel and verify the circuit-breaker’s screws are very firmly tightened on the power wires. Inexpensive and rapid fix.

 

[NickFie]

I think I found my problem. The X has been charging fine until last night. It tripped the breaker too.

I opened the HPWC and tightened the connectors from the charging cable. They didn't really seem loose but gave them a little nudge.

Checked the screw terminals on the breaker and load wire was really loose. I could have pulled free from the breaker. Tightened it down and so far so good.

Apologies. Looks like our posts crossed.

Glad it was an easy fix.

 

[DrDabbles]

At the same amperage?

Reviewing the video, the car was saying check the outlet or for extension cord. And it was charging at 105V and 9-12A from what I could catch by pausing the video. It did eventually stop charging. I thought it tripped the breaker, but it looks like maybe the charger or the car stopped the charging session.

 

[nwdiver]

Reviewing the video, the car was saying check the outlet or for extension cord. And it was charging at 105V and 9-12A from what I could catch by pausing the video. It did eventually stop charging. I thought it tripped the breaker, but it looks like maybe the charger or the car stopped the charging session.

Yeah... that's what I've seen my car do and how it should work. I've used bad or overloaded circuits at RV parks. If voltage drops too far it slows from 40 to 30. If voltage doesn't recover it slows again. If it still sags it stops. You cannot have melting and fire without a voltage drop so it's super effective.

 

[eprosenx]

Is your breaker box in an area that gets hot [in the summer]? House circuit breakers trip based on heat, so a breaker whose trip point is in the lower margins of it's design and is operating near 80% the nominal current capacity for extended periods of time can be pushed over the top by direct sunlight or something. Remember that a 50A breaker is supposed to trip if the current goes over 40A for a couple minutes (I forget the exact target spec), so drawing 40A continuous is right at the edge even though a lot of breakers won't trip until the current goes somewhat higher (the +/- manufacturing tolerances on these physical breakers is typically pretty bad).

As for the difference from the Model X, maybe the Model 3 is more aggressive about taking it "to the line" and relying on the A/C to keep the battery and power circuits operating safely? Maybe the Model 3 is able to draw that power continuous for longer periods of time, compared to the Model X?

FYI- A 50a breaker should hold the full 50a load indefinitely under “standard test conditions” which I believe is 104F. Now the reason that we derate to 80% for “continuous” is that those standard test conditions have the breaker installed in a panel with no adjoining breakers to stifle heat dissipation.

In the real world, breaker panels can be really hot inside them and the adjoining breakers may be hot themselves due to high loads of their own. So by only loading to 80% you are adding in a margin of safety to avoid nuisance trips.

So the moral of the story is that if you load a 50a breaker above 40 amps (but still 50a or below) you are rolling the dice as to when or if it may blow.

Inside a residential circuit breaker there are two trip mechanisms. One is the short circuit “fast” blow one which is electromagnetic. The other is bimetallic strips that heat up differentially and “bend” which causes the trip. They inherently have tolerance issues. Breakers are not particularly precise devices.

Also note: After several accidental trips I know of many professional operators that require the breakers to be replaced. They are not designed for regular repeated operation.

I am really glad you found the issue! As per usual, the insulation fails before the copper.

I would probably replace the breaker for good measure after heat exposure from be bad connection and the repeated blowing. (cheap $10 insurance) also, make sure the wire is still OK

 

[eprosenx]

Funny you mention it - because this just started happening to me. A couple of times now, the breaker trips after maybe 30 minutes or so. My subpanel is about four years old - a Square D Homeline with 50 amp HOM double pole breaker protecting a NEMA 14-50. I use a JESLA which is a Gen 1 UMC with a J1772 grafted on to it. Been using it daily with our Volt for several years without problem.

I am dialing down the current to 36 amps. Voltage is low 240s.

Considering redoing the setup to a 60 amp connection with wall charger. Then buying a Tesla-J1772 "JDapter" so I can charge the Volt with it.

This should not be happening. Replace the breaker and tighten the terminals properly (and inspect the panel at the same time to make sure your bus is not damaged or anything causing heat from the bus). This should solve your issue.

(Btw, I love my wall connector, so don’t let me talk you out of that route either - I am just suggesting that your issue is easily fixable for cheap)

 

[DrDabbles]

Then I opened the panel with the 50amp breaker and could see the legs coming out of the breaker to the HPWC had a clear plastic coating over the white/red coating. The clear coating was cracked and pulling away from the wire. I could tell this was heat damage. Checked the screw terminals on the breaker and load wire was really loose. I could have pulled free from the breaker. Tightened it down and so far so good.

You very likely need to replace that breaker. If enough heat was being generated in the wire itself to melt the insulation, then that breaker is likely damaged internally. If the resistance in the wire was high enough to burn the ends near the breaker, it is very likely the insulation is damaged elsewhere. You really need to call a professional, have them look at the damage, and get their opinion on the situation. If you have 12 kW of energy and potentially damaged insulation, someone can be seriously hurt or a fire can start.

You should also try to read the wire gauge from the insulator. If the gauge is too small, it can cause more thermal expansion and contraction than you'd expect under normal circumstances. This can lead to the terminals working loose over time. There are recommended torque specs for these devices, but really it should just be screwdriver tight and not overtightened.

Anyway, burnt insulation is a HUGE red flag, and I really cannot stress enough that you should get a professional opinion on your situation. An inexpensive visit from a local spark is so much cheaper and easier than an insurance claim for a car or home that burned down.

Edit: A youtube electrician talking about a similar issue. Replace that breaker ASAP at the very least.

 

[eprosenx]

The continuous load spec is I believe 3 hours.

Yes, this is the definition by which NEC defaults to in order to determine if something is a "continuous load" and hence needs to be calculated as if it was 25% larger of a load (since it runs for a long time and does not give the wire/breaker/etc time to cool between runs).

The NEC specifically designates all EVSE charging units (like the UMC or Wall Connector) as continuous loads since they are expected to run for hours on end at full load to charge cars.

 

[eprosenx]

• Test the voltage between the two hot legs. The value should be within 3% of 240v.
• Test the voltage between each hot leg and ground. The values should be within 3% of 120v.
• The maximum voltage drop should not be more than 5%. If it is, it violates the NEC, and it could be a clear cause for your problem.

I am going to challenge this line of thinking. Yes, the numbers are technically correct above, but applied incorrectly. The numbers above are *recommendations* in the NEC for voltage drop in feeders and branch circuits. (a feeder being the line from your main service to a subpanel and the branch circuit being from the last subpanel out to the end device) So a given feeder should not be more than a 3% drop and a given branch circuit not more than a 3% drop, but in aggregate it should not be more than a 5% drop (i.e. if you end up with a feeder with a 3% drop then you need to plan all branch circuits downstream of that subpanel with only 2% drop).

Now with that being said, the bigger influence here is likely to be the voltage your utility delivers. This can be within a pretty wide range. The utility itself is targeting 240v nominal, but this can range + or - 5% by itself (or even more for short durations!). Each utility may have its own standards, but PGE actually does quite a good job in documenting their targets:

https://www.pge.com/includes/docs/p...ergystatus/powerquality/voltage_tolerance.pdf

So your utility may say deliver power all the way down to 228v and be within spec. Your voltage losses within your house wiring are then *on top* of that (say down to 216.6 in that example).

Test procedure wise, measure your voltage two places before charging:

• At the main electrical service (typically your main panel)
• At the HPWC

Then start charging the car. Measure the voltage again at the HPWC and compare. This tells you how much total drop is happening when you place load on the circuit. But then measure at the main panel again as well. The delta between the previous and the new measurement tells you how much of the loss is "upstream" of your branch circuit.

FWIW, calculating loss on an electrical wire of a certain gauge and length for a given load is a VERY well understood thing. The NEC has formulas for it (and that is where the loss calculations to stay within 3/5% come into play)

Now with ALL of that being said.

THE NEC DOES NOT HAVE REQUIREMENTS ON VOLTAGE DROP

It has recommendations. Not requirements. Big difference. They don't see the issue as much as one of a danger. Instead it is more a functionality issue, a lot of devices won't work well or suffer reduced lifespans if voltages are too low.

If your voltage drop is over 3% or the feeder/branch wire is getting hot, it's very likely that the circuit was not installed with the proper wire gauge somewhere between the panel and the HPWC. This can cause a fire. Wire is rated for temperature ranges, and if yours is getting hot it can melt the insulation off, short out on the conduit or inside your walls, and someone could get hurt or die. Nobody should be messing with an electrical circuit that doesn't behave properly.

This is mostly correct, but it is also very possible and easy to have over 3% loss in a circuit just by having too long of a wire. While yes, this violates NEC recommendations, it is not a REQUIREMENT. While yes, if you have a lot of loss in a circuit that is not explained by the circuit length this likely indicates an overheated terminal or something (which is dangerous!), but if you just have a long circuit then the loss that causes the heating is spread out over the entire length of the wire and is factored into the load calculations for that wire. Wires warming during operation is how things work. The issue is about making sure they don't heat up TOO much (which is what reams of rules in the NEC are written to avoid).

So now on to my most important comment:

While inefficient, I don't think that voltage loss in really long circuits is any kind of a danger. In some electrical motors, if the voltage is low they will draw more amperage to compensate in order to keep spinning at their operating speed. But with a Tesla, it will always draw a precise amount of amperage from a circuit. If the voltage drops then it just charges the car slower (same # of amps, but at lower voltage the total amount of energy it can consume is reduced). I have heard of folks with over a couple hundred feet of wire in order to get to their parking garage from their condo. While not optimal, it should be fine.

The practical issue is that the Tesla vehicles are comparing voltage from when they started charging to the current voltage as they charge. Since the vehicle has no idea *why* voltage is dropping, it assumes any drop over a certain amount is due to a dangerous situation and it will backoff the charge rate or stop charging to reduce the risk. So if you drag the voltage down too much due to a really long wire you may run into this issue.

It is also worth noting that at certain times of day it may be just fine (right on the edge of what the Tesla will accept), but then maybe changing grid conditions during peak time of day cause it to trip.

So following the NEC guidelines is generally a really good idea, I could see cases in which you might be willing to go outside their specs for the specific special use case of EV charging.

Larger gauge wire gets more expensive in a hurry! (not to mention larger conduit costs and labor costs to run it) Have you looked at the price of copper lately?

I am curious if there is a true financial case to be made around wire upsizing due to the ongoing operational costs of energy loss. Where I live, power is pretty cost effective so the payback period may be a really long time in many situations.

 

[RedModel3]

If your voltage drop is over 3% or the feeder/branch wire is getting hot, it's very likely that the circuit was not installed with the proper wire gauge somewhere between the panel and the HPWC. This can cause a fire. Wire is rated for temperature ranges, and if yours is getting hot it can melt the insulation off, short out on the conduit or inside your walls, and someone could get hurt or die. Nobody should be messing with an electrical circuit that doesn't behave properly.

If the voltages measure properly, the ammeter doesn't read above 40A, and the hot legs in the circuit aren't getting temperature hot, then it's just as likely that your breaker is garbage and too sensitive. The fact that your other Tesla doesn't cause this issue can be attributed to a million different variables that we simply don't know without detailed measurements being taken. Either way, if there's something wrong with the circuit, please stop tempting fate. People lose property and die due to electrical fires, and it's not worth the risk. Get an electrician to look at the circuit, tell them what you're trying to do, and let them make a recommendation to you.

This a million times! This actually happened to me the second night I had my car. I had a wall charger hooked up to a 50A subpanel, and sometime during the second night of charging, everything connected to the panel went dead. I couldn't find any breakers or GFCI's to reset, so I called my electrician. After a few holes sawed in the basement ceiling, they found two connections between the subpanel and the main panel. The first box featured a lovely connection between the 50A wire and a 15A wire. The second box dialed that down to a 10A wire. Factor in also that something else was running from the subpanel that wasn't listed, and it turned out that I was trying to pull 60 amps through a 10 amp wire!

Keep in mind also, this 50 amp subpanel had been installed with a permit, about 15 years before I bought the house. It should have burned down long ago. It almost finally did start a fire, just as described above. The copper completely melted.

Just because your X charges fine doesn't mean there isn't a problem somewhere. That damned 10 amp wire had run a dryer, pool pump, lights, and outlets for 15 years. I had been charging my Volt every night for several months. Whatever God there is was certainly watching out for me.

 

[eprosenx]

This a million times! This actually happened to me the second night I had my car. I had a wall charger hooked up to a 50A subpanel, and sometime during the second night of charging, everything connected to the panel went dead. I couldn't find any breakers or GFCI's to reset, so I called my electrician. After a few holes sawed in the basement ceiling, they found two connections between the subpanel and the main panel. The first box featured a lovely connection between the 50A wire and a 15A wire. The second box dialed that down to a 10A wire. Factor in also that something else was running from the subpanel that wasn't listed, and it turned out that I was trying to pull 60 amps through a 10 amp wire!

Keep in mind also, this 50 amp subpanel had been installed with a permit, about 15 years before I bought the house. It should have burned down long ago. It almost finally did start a fire, just as described above. The copper completely melted.

Just because your X charges fine doesn't mean there isn't a problem somewhere. That damned 10 amp wire had run a dryer, pool pump, lights, and outlets for 15 years. I had been charging my Volt every night for several months. Whatever God there is was certainly watching out for me.

Oh my god, I am so glad you are OK. This is the definition of a recipe for a fire!

I can’t belive anyone would do that. This is how you kill people.

So was the wire in conduit??? How did this *not* start a fire?

Also, I am kind of surprised the Tesla did not see voltage drop and backoff or stop charging?

Maybe as a 10a wire it melted before the Tesla had time to react? Or maybe this was before Tesla implemented a lot of the safety logic it has now?

 

[wws]

I pulled the cover on my sub-panel. (Don't worry - I am quite familiar with house wiring and turning off breakers for safety.) Found that on both sides of the breaker I could tighten the screws by maybe 1/8th of a turn. Same with one of the poles of the breaker for my solar system. (We installed the sub-panel when we did solar a few years ago.) I doubt if it was enough make a difference, but we'll see.

Also pulled the 14-50. All its screws were already nice and tight. The wires between it and the breaker are only about a foot or so long, and are #6 AWG THHN.

 

[eprosenx]

I pulled the cover on my sub-panel. (Don't worry - I am quite familiar with house wiring and turning off breakers for safety.) Found that on both sides of the breaker I could tighten the screws by maybe 1/8th of a turn. Same with one of the poles of the breaker for my solar system. (We installed the sub-panel when we did solar a few years ago.) I doubt if it was enough make a difference, but we'll see.

Also pulled the 14-50. All its screws were already nice and tight. The wires between it and the breaker are only about a foot or so long, and are #6 AWG THHN.

Hrm, likely worth the $10 to replace the breaker. If you have been charging an EV for years on it then it may just be beat up a bit.

I fear that with EV charging we are going to find many electrical components that were “good enough” for typical home electrical use but that just don’t stand up to regular constant load and cycles from an EV.

I particularly wonder about the 83 percent rule that lets you undersize the main electrical conductors into a house beyond what the calcs say you need. Basically at some point in the code they decided that we were drastically oversizing conductors into houses and under utilizing them and so it appears to me they just made this one off rule that you can reduce the conductor size by 17% for residential feeds rather than going back and adjusting all the load calculation formulas. Very odd.

I am wondering if EV’s are going to test that rule as they become more popular and they change the load dynamics in residential.

 

[wbhokie]

This a million times! This actually happened to me the second night I had my car. I had a wall charger hooked up to a 50A subpanel, and sometime during the second night of charging, everything connected to the panel went dead. I couldn't find any breakers or GFCI's to reset, so I called my electrician. After a few holes sawed in the basement ceiling, they found two connections between the subpanel and the main panel. The first box featured a lovely connection between the 50A wire and a 15A wire. The second box dialed that down to a 10A wire. Factor in also that something else was running from the subpanel that wasn't listed, and it turned out that I was trying to pull 60 amps through a 10 amp wire!

Holy crap! Thank god nothing caught fire. This is a nightmare scenario. At least they didn't use a coat hanger.

 

[wws]

Hrm, likely worth the $10 to replace the breaker. If you have been charging an EV for years on it then it may just be beat up a bit.

If I see the problem again, replacing the breaker may be a step to consider. I don't like swapping parts that I haven't proven bad though. I also may disassemble the J1772 plug and see if there is anything inside that could be reworked.

I fear that with EV charging we are going to find many electrical components that were “good enough” for typical home electrical use but that just don’t stand up to regular constant load and cycles from an EV.

Folks charging at 120v have already been seeing this for a while. It is why GM and others have started putting thermal sensors in their EVSEs plugs. Those cheapo $0.39 "residential grade" receptacles should be immediately tossed and replaced with spec-grade (e.g., commercial, industrial, or hospital grade) versions.