Nema 14-50 w/ 40Amp Breaker Still Tripping w/ Car limited to 32Amps?

[BaileyDog12]

Newbie here. My home was built in 2005 so it was prewired with a 40AMP Breaker and wiring in place specifically for a future EV vehicle. I installed the NEMA 14-50 outlet myself since the wires were just tucked away ready for future install of an outlet. It took all of 5 minutes.

So I took delivery of the car last week (yeah!!!) and start charging at 40 AMPs. Of course it trips after 1 hour because I have a 40 AMP Breaker (I learned this after the fact that a 40Amp breaker should be limited to 32Amps). So I read up and learned I should be charging at 32AMPs and adjusted that from the car's max capacity charge.

Things were good for 2 nights and I was getting 23-25 miles per hour charge at 32Amps. Then bam, it trips again last night. I reset the breaker this morning and it charges for 30 minutes and it trips after another hour.

So tonight I cranked max charge down to 25Amps just to be super careful. So far so good and car is now fully charged.

Anyone run a 40Amp breaker on a 14-50 outlet? What max charge are you getting? I'm not sure if I have 6 or 8 gauge wires at the moment, but I figure if I'm limiting it to 32Amp charges it should be within specs regardless.

 

[mblakele]

I would have an electrician check it out. That might cost a few bucks, but it's cheaper than an electrical fire.

 

[cman8]

I run mine with a 40 amp breaker on a 14-50 nema connector. Havent tripped it yet. do you plug it in at night when nothing else is running? I know on my panel, I could handle the 40 amps but its only a 200 amp panel so If I run my range and dryer I would probably trip the breaker. Also wire is a big factor in it too.

 

[BaileyDog12]

I would have an electrician check it out. That might cost a few bucks, but it's cheaper than an electrical fire.

Haha the wife tells me the same thing. My brother in law is an electrical engineer and he has a Benz B class and loves EVs. Might have him come out to take a look before I get the electrician out.

 

[csshih]

It could also be a bad breaker that trips early.

 

[BaileyDog12]

I run mine with a 40 amp breaker on a 14-50 nema connector. Havent tripped it yet. do you plug it in at night when nothing else is running? I know on my panel, I could handle the 40 amps but its only a 200 amp panel so If I run my range and dryer I would probably trip the breaker. Also wire is a big factor in it too.

Yeah i charge at 2am when nothing else is running. The wires are at least 8 gauge as they were really thick. Running 32amps on a 40amp breaker on 8 gauge should not be tripping. My amp panel is 240...

It May be just a bad breaker since it sat unused in the panel for 11 years till now since I never had an EV before this or anything above 30 amps has too much flux for the 40amp breaker.

 

[mudfud]

that's interesting that your tesla "forgot" the charge max at your location. mine did this also about 2 weeks ago after an upgrade.

I have a 30 amp chargepoint in the driveway that I use an extension J1772 adapter to plug the Tesla EVSE into. granted, the plug on the EVSE is the nema 14-50, however, at this location, I have used this setup before and set the max charge to 30 amps.

started a charge and it quit due to the chargepoint being unable to maintain over 32 amps for charging. I found the car set for 40 amps.

i've never charged at 40 amps in this location. odd.

 

[dhrivnak]

Try a net breaker as there are bad ones out there. You should be able to pop one in for $20 or so. If your woes are 8 Gauge you should be done with a 50 amp one to give you more margin. Also chech for heat. If the breaker or outlet get warm you may have a bad connection which will caus e heat and add to the tripping.

 

[ABCCBA]

@BaileyDog12 if you truly have a 14-50, install a 50 Amp breaker and charge at 40A, assuming you sized the conductors for 50 amps. Also, there is an approximate 20% loss for AC to DC conversion. So a 40A circuit only charges at 32A. A 50A circuit charges at 40A.

If you are comfortable, pull the breaker panel cover and confirm your conductor size. See what guage it is to determine its ampacity before changing your breaker. Again, if the conductors are rated for a 50A service, which they should have been using a 14-50 outlet, then up the breaker size to 50A and you should be fine. As always, if you are uncertain, contact an electrician. I have a 14-50 on a 50A breaker and a HPWC on an 80A breaker.

Newbie here. My home was built in 2005 so it was prewired with a 40AMP Breaker and wiring in place specifically for a future EV vehicle. I installed the NEMA 14-50 outlet myself since the wires were just tucked away ready for future install of an outlet. It took all of 5 minutes.

So I took delivery of the car last week (yeah!!!) and start charging at 40 AMPs. Of course it trips after 1 hour because I have a 40 AMP Breaker (I learned this after the fact that a 40Amp breaker should be limited to 32Amps). So I read up and learned I should be charging at 32AMPs and adjusted that from the car's max capacity charge.

Things were good for 2 nights and I was getting 23-25 miles per hour charge at 32Amps. Then bam, it trips again last night. I reset the breaker this morning and it charges for 30 minutes and it trips after another hour.

So tonight I cranked max charge down to 25Amps just to be super careful. So far so good and car is now fully charged.

Anyone run a 40Amp breaker on a 14-50 outlet? What max charge are you getting? I'm not sure if I have 6 or 8 gauge wires at the moment, but I figure if I'm limiting it to 32Amp charges it should be within specs regardless.

 

[Chickenlittle]

Newbie here. My home was built in 2005 so it was prewired with a 40AMP Breaker and wiring in place specifically for a future EV vehicle. I installed the NEMA 14-50 outlet myself since the wires were just tucked away ready for future install of an outlet. It took all of 5 minutes.

So I took delivery of the car last week (yeah!!!) and start charging at 40 AMPs. Of course it trips after 1 hour because I have a 40 AMP Breaker (I learned this after the fact that a 40Amp breaker should be limited to 32Amps). So I read up and learned I should be charging at 32AMPs and adjusted that from the car's max capacity charge.

Things were good for 2 nights and I was getting 23-25 miles per hour charge at 32Amps. Then bam, it trips again last night. I reset the breaker this morning and it charges for 30 minutes and it trips after another hour.

So tonight I cranked max charge down to 25Amps just to be super careful. So far so good and car is now fully charged.

Anyone run a 40Amp breaker on a 14-50 outlet? What max charge are you getting? I'm not sure if I have 6 or 8 gauge wires at the moment, but I figure if I'm limiting it to 32Amp charges it should be within specs regardless.

Careful. May not be as simple as changing breaker. You need to look at size of wire used to run to the outlet. Need 6-3 wire. If your not sure what that is than get help

 

[Mango]

Sounds like a bad breaker. OR wire is to small for the load. Wire heating up tripping the breaker.

Check the wire size. If you do not know what you are doing, hire a someone. Electrical fire and Tesla do not go well together.

Let us know what it was.

 

[FlasherZ]

If you are comfortable, pull the breaker panel cover and confirm your conductor size. See what guage it is to determine its ampacity before changing your breaker. Again, if the conductors are rated for a 50A service, which they should have been using a 14-50 outlet, then up the breaker size to 50A and you should be fine. As always, if you are uncertain, contact an electrician. I have a 14-50 on a 50A breaker and a HPWC on an 80A breaker.

Minor correction: it is perfectly legal to have a 50A receptacle on a 40A circuit, *if* the only load to be attached is nameplate rated for a 40A circuit. This is common for electric ranges and ovens in homes. What makes its use illegal is when you violate the nameplate by attaching a larger load to it - i.e., the Tesla UMC. So when you say "which they should have been using a 14-50 outlet", that isn't necessarily correct.

Technically, the only legal way to use the Tesla UMC on a NEMA 14-50R receptacle is to attach it to a circuit rated for 50A, protected by a 50A fuse or breaker. In the US, it requires #6 if NM cable / Romex or #8 if wire-in-conduit.

The cars are known to occasionally "forget" their charging current - either due to software upgrade, wrong detected location, etc. This is why you can't rely upon user-configured current (and the code doesn't recognize user-configurable current on the nameplate).

To the OP: breakers are occasionally bad out of the box and can trip earlier than expected. I would consider replacing the breaker if there is no other sign of trouble or other problems (e.g., a breaker shared by two loads).

 

[gaswalla]

So, I used to believe my home wiring was less than perfect... It turned out to be the UMC. I realize you have a new UMC, but I would get it checked out by the service center. You could try charging in another nema 14-50 and see what happens.

 

[TexasEV]

@BaileyDog12 if you truly have a 14-50, install a 50 Amp breaker and charge at 40A, assuming you sized the conductors for 50 amps. Also, there is an approximate 20% loss for AC to DC conversion. So a 40A circuit only charges at 32A. A 50A circuit charges at 40A.

It has nothing to do with AC to DC conversion. It has to do with continuous load. A circuit has to be 125% of what a continuous load will be. Your numbers are right but the explanation is wrong.

 

[Solarwind]

Just replace the defective breaker and all will be well.

 

[BaileyDog12]

Thanks to everyone for their replies. Great community and I closely read all the feedback. Totally helpful and I'll update when I've resolved the problem.

 

[L-P-G]

There is one very important thing i haven't seen mentioned, before you remove the cover and the breaker, turn off you main feed to the panel. You don't even get a single chance with 240 before you die.

 

[FlasherZ]

There is one very important thing i haven't seen mentioned, before you remove the cover and the breaker, turn off you main feed to the panel. You don't even get a single chance with 240 before you die.

When you take the cover off a service panel (main home panel, not a subpanel), there are still bits that will still be live in it anyway - especially the lugs at the top.

 

[L-P-G]

It depends on your house, my house has a main panel outside where the meter is, attached to it there is a 200A breaker. I turned that one off when i installed my receptacle.

 

[FlasherZ]

It depends on your house, my house has a main panel outside where the meter is, attached to it there is a 200A breaker. I turned that one off when i installed my receptacle.

While some do, many don't. In your case, the panel inside is a subpanel and you can indeed turn it off. But in most homes outside of hurricane or earthquake areas, you'll find that the conductors enter from the meter to the service panel inside and will be live with the cover off.