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Does Tesla mobile connector work with 40Amp breaker

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If the picture of the 242(3)V number at the breaker is under load (how much current does the car indicate?), and 246V is an open-circuit measurement (no load), that's also bad, and points to the breaker being bad, or something upstream of the breaker. 4V of drop across a breaker is a problem, especially if you're drawing 32A (you would feel it getting very hot). You can measure (carefully!) on the main bus bars on the panel at the same time you are drawing current to debug, if it gets to that point. But not yet.

In any case, just look at the car's voltage measurement at various current draws. That's step 1.

Ditto to the comments about measuring voltage at the breaker and at the main bus bar while the car is drawing load (and while it is not drawing load is useful too).

I would not be concerned if the voltage is 246v at the breaker with no load, and 242v under load. That could just indicate that the feeder to that panel or any upstream service feeder back to the transformer has some loss to it. Those numbers don't concern me in the slightest and are fully within spec.

But yes, if there was significant voltage drop between the bus bar voltage and the output of the breaker I would be concerned. That would likely indicate a bad breaker or it having bad contact with the bus bar.

(also note that utility voltage fluctuates throughout the day so you should be taking your readings at as close to the same time as possible - and also note your meter may be calibrated differently than the car so you can't necessarily directly compare numbers between the two)
 

Hmm. I don’t know what are the failsafe modes of the adapters. Could be something wrong with the signaling but maybe someone here has seen one fail?

I don’t remember the allowable range of the “set limit” function. Click “set limit”, adjust the current. Try to set it to 4A if possible, and provide the voltage the car indicates. If you can’t adjust the limit lower, adjust the charging limit below current charge %, and current should drop to 2A (at least momentarily) if climate control is off.

If the voltage goes up enough with reduced current, it would mean excessive resistance. My car shows about 4V (243V->239V) drop for an increase in current of 21A (2A -> 23A). (~0.2ohms - I have 6-gauge wire, so I assume a significant portion of that is the UMC cable but have not measured at the outlet concurrently) Hopefully you don’t see a steeper slope.

But overall, it seems like maybe you do have an adapter problem. If there were a big problem I guess I would expect lower voltage even at 8A. It seems like open circuit was 246V (measured by a different device though, making it not comparable). Just one more data point and then hopefully we know. Again, maybe someone has seen an adapter fail?

Any other ideas?
 
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I just ran the math on 48 amps of draw at 240v across a 6 awg wire at 65 feet of length. I get 1.15% of drop which is well below the recommended maximum drop of 3% (technically it is 3% or a total of 5% between the feeder and the branch circuit and no more than 2% for each in either case, but you are well below both - a feeder only applies if you have a subpanel).

So you are vastly within limits at 6 AWG. Also, the voltage drop aspect of NEC is actually only a recommendation and not a code requirement. In the case of a Tesla, it will ONLY draw "X" number of amps regardless of voltage, so it is not like if the voltage drops due to conductor length that it will draw more amps. It still will draw the same number of amps and just charge slower.

The energy that is lost due to that voltage drop is lost over the entire length of the wire and so it can easily dissipate it over such a long distance. Properly sized wires do get slightly warm sometimes, but not HOT.

There is absolutely nothing wrong with upsizing to #4 AWG if you want to, but I would have zero concerns sleeping at night with #6 AWG when used for 48 amps of EV charging (this is literally exactly what I have at my house - also in 3/4in conduit to a Wall Connector).

As to the Kia Nero EV- How would you hook that up? Would you put in a subpanel with a second charger? Or would you do a second Wall Connector and have them load balance?



Absolutely code compliant and not a fire risk as long as your EVSE does not tell the car it can draw anything above 32 amps. Setting it in software in the car I do not believe counts.

I personally recommend against installing new 6-50 receptacles or 14-50 receptacles on anything less than a 50a circuit, but I also don't tell people to go spend money changing it if they already have it installed since it is fully code compliant and as long as they don't use an EVSE that is capable of drawing 40 amps.



Yes, technically the resistor is in the adapter on the end of the UMC. It tells the UMC how many amps the receptacle it is plugged into is in theory rated for (this of course has nothing to do with what the wire or breaker ACTUALLY are). Then the UMC passes a signal to the car over the J1772 protocol telling it the max charge rate limit it is allowed to draw. It is the CAR that is actually choosing what to draw. It should NEVER go over what the EVSE tells it that it is allowed. The car of course can choose to draw less if it wants (like based on your software setting).



This is incorrect. You absolutely are allowed to have a 40a breaker and wire on a 50a receptacle as long as the thing you intend to plug into it only needs 40a or less (32a continuous). (so no UMC Gen 1's) As stated before, I don't recommend folks install these kinds of circuits new, but sometimes if there is existing wiring in the walls it can be an extremely cost effective (and safe) option. I personally would probably label it clearly if this was the case.

Here is the relevant code sections from the 2017 NEC:
View attachment 358996

Here is (B) referenced from above (A did not apply)
View attachment 358997

And here is just a blurb about what you are allowed to connect in. This becomes vastly more complicated with a lot more rules if you have more than one receptacle on a circuit (which is not allowed by article 625 of the NEC which pertains to EV charging).
View attachment 358998
Thanks for the detailed explanation.

Concerning the Kia Nero EV...I plan on load balancing it the best I can.

Unfortunately the Kia will charge as soon as you plug it in. There is no delayed charging opportunities. So.....with that said...I'm going to schedule my P3D+ to charge somewhere around 1 or 2AM. The Kia will get plugged in around 6PM every day.

That's the preliminary plan - subject to change.
 
There is an exception in the NEC (Nat'l Electrical Code) allowing a 50 amp receptacle on a 40 amp circuit. I'd guess it is there because there are no common NEMA 40 amp receptacles. So you are 'code compliant'.
Yup, you are code compliant but it's now up to you (or the UMC) to make sure you do not draw more than 40A, or 32A continuous, from the 6-50 receptacle. Might want to make a note and tape it next to the receptacle in case someone in the future thinks it's ok to draw 50A from it. If you don't, the breaker will definitely trip... or worst case... FIRE. To mitigate, you may want to use 6AWG wire instead of the recommend 8AWG for 40A.
 
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8 gauge THHN wire in conduit is allowed to be used at its 75c rating which allows for 50a. So it is perfectly legal to use on a 50a circuit.

8 gauge NM cable (romex) is only allowed to be used at the 60c rating which limits you to a 40a circuit.

A 40a circuit is utterly and completely legal on a 6-50 or 14-50 receptacle as long as the intended load is not greater than 40a (32a continuous). So a UMC Gen 2 is totally fine. A UMC Gen 1 is NOT fine.

Sure, 8ga THHN is OK if everything is 75C rated (which a 14-50 outlet isn't guaranteed to be 75C rated). Breaker box is usually going to be OK, since those are typically 60/75C. But, if I'm going to assume what kind of wire is drawn, it's going to be Romex. THHN is just pricier.

Also, sure, if you 'intended' to only ever pull 40A it's fine, but generally speaking that's not a great guarantee. Who knows what happens when you sell the house, or if someone else plugs something into it. I guess adding a very clear marking could help.

My point is: without any other markings on it/explanation, a 40A breaker to a 6-50 shouldn't pass code because it should be assumed you will try to draw max load out of it. I guess you could originally get it to pass inspection if you "intend" to only pull 40A (32A cont) out of it, but what about the next guy that inherits it? It's pretty dangerous to not mark it clearly. If it's marked at 40A max only, then we're all good. Sounds like this was NOT the case for OP since he doesn't mention any of that.
 
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Not sure how to check the voltage during load, but I hooked the Tesla mobile connector to outlet and then checked the reading on outlet , it’s 242 just like at breaker.

With no load the voltage at breaker vs. at the outlet should always be nearly identical unless something is horribly wrong.

Doing this under load is easy: just start charging the car and do the exact same thing you're doing right now. Once it's loaded up you should see voltage drop compared to what it was unloaded. Even the car shows you as the voltage drops, which doesn't require doing that (which is pretty sketchy...)
 
From your pictures of the opened outlet...

I cannot see the ground wire going into the plastic conduit. It looks like plastic conduit. And it looks like the ground wire does not go into it. I'm not saying it doesn't, I just can't see it in the pictures. All I see is a ground wire from the ungrounded junction box to the receptacle. To me it sort of looks like it lazily loops from the outlet back to the green ground screw without entering the conduit. Hard to tell from two pictures.

As far as I know, there should be a ground wire back to the neutral/ground bus in the main panel! I've never used metallic conduit, perhaps it isn't required in that case (I do not know, but I personally would think a wire would still be required/preferred), but yours appears to be plastic so it isn't relevant anyway.

It may be just that your pictures didn't show the ground wire clearly.

I am fairly sure that there is an attempt by the UMC to detect grounding problems, though I don't know how it is done, since not having a ground is a good way to get electrocuted. Someone who is knowledgeable can comment if this remains relevant (meaning, if you actually have no ground).

@Kirby64 has the right idea for under load measurements. It's important that we know what the car is drawing for every picture you take otherwise it's not much use.
 
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With no load the voltage at breaker vs. at the outlet should always be nearly identical unless something is horribly wrong.

Doing this under load is easy: just start charging the car and do the exact same thing you're doing right now. Once it's loaded up you should see voltage drop compared to what it was unloaded. Even the car shows you as the voltage drops, which doesn't require doing that (which is pretty sketchy...)
Voltage with load i.e. car in charging mode is fluctuating between 239/238.
 
Sure, 8ga THHN is OK if everything is 75C rated (which a 14-50 outlet isn't guaranteed to be 75C rated). Breaker box is usually going to be OK, since those are typically 60/75C. But, if I'm going to assume what kind of wire is drawn, it's going to be Romex. THHN is just pricier.

Also, sure, if you 'intended' to only ever pull 40A it's fine, but generally speaking that's not a great guarantee. Who knows what happens when you sell the house, or if someone else plugs something into it. I guess adding a very clear marking could help.

My point is: without any other markings on it/explanation, a 40A breaker to a 6-50 shouldn't pass code because it should be assumed you will try to draw max load out of it. I guess you could originally get it to pass inspection if you "intend" to only pull 40A (32A cont) out of it, but what about the next guy that inherits it? It's pretty dangerous to not mark it clearly. If it's marked at 40A max only, then we're all good. Sounds like this was NOT the case for OP since he doesn't mention any of that.

I generally agree with you here, but I find nowhere in the National Electrical Code that has any kind of a marking or labeling requirement to identify a 6-50 or 14-50 receptacle that is only on a 40a circuit. While I absolutely would label this myself if I were to install a circuit like this, I just don't see it as a hard code requirement anywhere.

I would absolutely be in favor of a change to the code to add a marking/labeling requirement in this situation. (and you could even convince me that they should change code to not allow this practice for new circuits)
 
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Voltage with load i.e. car in charging mode is fluctuating between 239/238.

That seems ok, 1% or so drop, though presumably with only 8A draw based on prior picture...which to me doesn't actually seem awesome...that would imply you would see about 242V minus ~12V (4*3V) (230V) when drawing 32A - if the UMC would allow it. I guess that is 5% drop at full load (if you could achieve it) which sounds out of spec?

Please confirm status of your ground though. Sorry if we cross paths.
 
Looks normal to me. 4V of drop at 32A seems well within reason. Sounds like a messed up charger to me. Or, alternatively, you could have an intermittently bad problem. Wiring looks normal to me for a 6-50 (hot, hot, ground).

Note the OP has posted pictures showing his charging current is capped at 8A. So this is 4V drop with 8A.

I don't see the ground going into the conduit in the picture. We need more pictures or confirmation that the ground is there.