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50 AMP Breaker Tripping

Just installed a GE sub panel fed by a 70 AMP breaker at the main panel (8 inches away) and running 30 feet with #6 THHN to a NEMA 14-50 outlet. Car will draw 40 amps for 10 min or so and trip the 50 AMP breaker at the sub panel. Repeated this several times. Breaker and wires are warm, but not hot. Backed the car down to 30 AMPs and after about an hour get a warning that the car is experiencing charging problems, check source. I have this exact set up at another location and it works fine. Anyone have any experience similar to this?

This shouldn't be a marginal situation. I believe all of the install specs are exactly per Tesla recommendations. Yet, it's acting like the car is drawing more than it says. Any help appreciated.

I have a HPWC that is tied to a 100A breaker on a 100A subpanel. Yes, I get it - that's cutting it close. However, I have DIPed the HPWC down to a 40A breaker and dialed the car to a 25A draw, yet I still throw the subpanel most days. I haven't followed up because I'm upgrading the service on Monday to 400A, but I agree that the car may be drawing more than it says, at least at peak.

Where are you at? How old is the house? What else is drawing power when this happens? From who does your grid power come from?

I've heard some of the European's mentioning issues, but not in the US.

Call Service and have them check the logs based on date/'prox' time.

Sounds like a voltage drop under load but not all your symptoms match and the car should indicate poor line or connection issues. You should have an electrician check voltage under load. The car logs might help so be sure to provide the Service Center the date and time to look at.

Sounds like a wiring fault somewhere. Is the 50A breaker new? If not, get a new one. Double check all connections from the 14-50 to the breaker, and the sub to the main panel.

So, this is a 15 year old house, all current wiring with a 400A service. Before the breaker trips, the car says it is pulling between 40 and 41 Amps at around 245 volts. The voltage fluctuates from 246 down to about 244, which seems relatively stable if not on the high end of the normal range.

The sub panel is new and dedicated to only Tesla charging. There are no other breakers or loads. I would think if my wiring were faulty somewhere, the breaker would simply trip regardless of load from the Tesla, but without the charger connected the wiring and breaker are stable.

The 50A breaker that is tripping while charging is brand new. I recreated the failure this morning and used an infrared temp sensor on the breaker at the point that it tripped. The breaker temp never got above 38C, which is starting to make me think I either have a faulty breaker or there is something in the charge cord that is momentarily causing a short that trips the breaker. I don't know if it's common for new breakers to be faulty, but I'll pick up another one and try replacing it.

Has anyone had any trouble with the mobile charge cable malfunctioning? There is obviously some sophisticated switching happening in that cable, so it seems plausible that a bad cable could be the source of all of this. Thanks for all the input.

Sure, could be the cable, the breaker, etc. Swapping out things to isolate the problem sounds like a good idea. Given your minimal voltage drops and heat, it does sound like either the breaker or UMC/cable.

.02cents... All circuit breakers must be derated for service... My understanding is that value is 20%, so your 50 needs to derate 20% or 40amps, just what your charging at. My understanding is that number 6 is rated for 50 amps therefore you could up the breaker to 60amps and when derated you can serve 48amps to the car.

Since you're using a NEMA 14-50, only a 50 amp breaker is allowed with the electrical code. A 60 amp breaker is a very bad idea as this is a protection circuit. I agree with others that the breaker is likely bad, although surprising as it new.

The circuit derating is for continuous current - so a 50 amp circuit/breaker can support 40 amps of continuous current (i.e. 80%), as you typically use with the UMC. This is the US standard, and Europe does not follow this approach (nothing wrong with European standards, just handled differently).

Perhaps suxcurmudgeon was thinking of a HPWC, which can support up to 80 amps with a 100 amp breaker and appropriate wiring.

Actually, suxcurmudgeon, I was thinking exactly that. The only thing not rated for 60 amps in this equation is the NEMA 14-50, but since the car is only (theoretically) pulling 40 amps, it shouldn't matter. I was thinking the 60 amp breaker would at least eliminate the possibility that we are pushing that 50 amp to its edge and that's the problem. It just bugs me to put more breaker in the loop than is technically necessary. I'll give that a try, though. Thanks.

To TeslaTap's point, I'll try the 60 just to see if that fixes the problem. If it does, then I'll switch to another new 50 amp and see if that works, too. If not, then at least I've narrowed the problem. I do agree that it isn't "code" to use the 60, but from a practical standpoint, the only thing in the circuit that isn't rated to handle 60 amps is the actual outlet.

Does anyone know an easy way to identify whether the breaker is being asked to supply more than 50 amps? I've seen loop style amp meters that can wrap around the wire close to the breaker. If the breaker is OK, then shouldn't I be able to see more than 50 amps being drawn prior to tripping? Seems like that would tell me it's the mobile cable or a loose connection or partial short somewhere in the new wiring.

I wouldn't update the breaker to 60A because (a) as TeslaTap points out, code says not to, and (b) your masking a potential problem. Get a clamp-on ammeter and measure the load at various points in the circuit to confirm the cars readout. But I'd strongly suspect the 50A breaker is bad. Bad ones do slip through quality control occasionally.

A digital clamp meter will read the current at the breaker.

I would simply try replacing the breaker and see if that resolves the problem.

Clamp on meters work great, but I doubt you will figure out anything. If there is an intermittent short somewhere, it will trip the breaker faster than you'll see it on the meter. It will confirm the exact current being drawn, but since you're not seeing any thermal issues, I doubt it's an over-current issue.

Let us know what you find out!

I'm having a similar intermittent problem. I have a HPWC on a 60 amp circuit breaker, but in a detached garage so there are also two 60 amp rated disconnects along the way. Normally, I get 48A and 11 kw to the dual chargers in my S85, but occasionally I see it dial itself down to 36A (8 kw), and a message gets displayed on the dash that the charging speed has been reduced, due to use of an extension cord or bad cable. The SC checked out the car, and suggest I have the power company come out and check, but I'm not sure what to have them (or my electrician) look for, other than checking all the connections, since the problem is intermittent and infrequent.

That is the message you would get if the voltage were low. Could be bad connections somewhere along the way (thermal imaging would show that), other loads causing an voltage drop, or simply low voltage from your utility.

Thanks for the insight, tes-s. I was wondering if it was a voltage drop, which I think may be a function of my utility (SCE). My power isn't very good, as the UPSes on my computers kick in all the time due to low voltage. My HPWC is on a separate meter all by itself.

I'll have my electrician check the connections, but perhaps this is something I'll have to live with, since I doubt I'll get Edison to do anything...

16thnch

I had a charging connector fail. However, it didn't trip the 50A breaker. Do you know if any Tesla owners are nearby? I would have borrowed a cable to find out if mine was the cause of my symptoms had I known someone to contact. The main battery was discharged after being plugged in overnight. Tesla Service thought the problem was more serious than it was, and came after the car.

@tes-s, I don't suppose you know what voltage is considered "low" do you, and for how long? Or how to capture this event at my panel, to demonstrate to my power company (SCE)?

I'm guessing the car thinks the current draw is causing the voltage sag, so lowers the current, when in reality, it is just a drop in my supply voltage. This wouldn't be so bad if the MS would ever try to increase the current again, but it seems I have to remember to do that manually on the charging screen for it to try...

Just took my car in for a tire rotation and addressed a few other issues. I use a NEMA 14-50 and have consistently charged at 40 A The last week or so it's been dropping down to 35-37 during charging. Didn't think it was a big deal but mentioned it anyway and brought my cable with me. The apparently detected multiple faults and gave me a new UMC. Got a repkacement a year ago for charging faults and have also had my car master charger replaced in October.

I don't know what voltage Tesla considers "low" to lower the current draw. Also not sure what the utility considers "acceptable" voltage.

If your UPS clicks in periodically, that could be an indication of power problems, an overloaded circuit, or something on the circuit with a heavy current draw (laser printer, for example).

16thnch,

Your problem lies in your first sentence. GE,
try a SQ D breaker

Mystery solved. Replaced the 50 amp breaker with another new one and it all worked without a hitch. I'm a little chagrinned that the first new one was bad, but hope this thread helps someone else facing the same thing. My conclusion is that an installation to charge a Tesla is one that will literally test the specification limits of your components. Everything in this installation was correctly specified, but the first 50 amp breaker was simply defective. For what it's worth, I checked the running temperature (via infrared sensor) of the placement breaker after about an hour of charging and it was around 43C (110F). Checking electrician web threads on breaker operating temp led me to understand that 50C to 55C is a good practical operating limit. The defective breaker was tripping at about 40C.

Agree with all the advice not to rely on using a 60 amp breaker because it is not to code. Glad it didn't come to that. Really appreciate the helpful contributors to this forum. You folks are awesome. Thanks.

I had exactly the same problem as 16thnch (apologies, I check in to this page every so often). Charging went fine first couple of weeks of ownership in April 2014, then breakers began tripping after 15-20 min of charging. Called electrician who had installed 50 amp line and new breakers from panel to garage. (Old house, tho wiring all new (4 years old) with 75 foot line to garage from new panel.). Electrician came that day and replaced the new breakers with newer breakers. Problem solved. Now late August, hasn't tripped since.

If/when I pull the trigger on a Model S, I'd surely get the electrics done waaaay before the car arrives. Without a Model S sitting in the garage, how do you know the electrician did his job properly? He will likely NOT do warranty work months later if you claim a breaker or wire is bad...

@panoz
that is what current owners are for. When the time comes, create a post with a title like this "would someone please come to my garage and charge for free". I'll bet your problem will be solved. :)

@panoz:

Talk with any prospective electricians. I had my NEMA 14-50 installed in late June. My electrician's default warranty was 30 days. Since my car won't arrive until the coming weeks and I don't have the means to check the circuit, he extended the warranty until the end of the year. No additional cost, and I got it in writing.

I agree with roseland67. It is the breaker. Change the box if you must. Get away from GE.

I have found that GE breakers, even brand new ones, seem to fail much more frequently than other brands. Depending on the model of breaker, you may be able to find another brand which is an exact replacement for your GE. I have not tried that, but have been tempted to.


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