Does Tesla mobile connector work with 40Amp breaker

[AlanSubie4Life]

I was getting 5 flashes which indicates reduced power. It’s the same alert on the car screen too.

Sorry, there is a lot of cross chatter here which makes it difficult.

1) Confirm status of the ground.
2) Confirm your car was drawing 0A (or 2A???) when 242V was measured at the outlet, and was drawing 8A when 238V was measured at the outlet.
3) In the same situation (car drawing 0A, and car drawing 8A), measure the voltage at output side of the breaker outlet (where you measured before).
4) In the same situation (car drawing 0A, and car drawing 8A), measure the voltage at the INPUT side of the breaker...looks like it might be a little difficult for you since it looks like you have a double row of breakers...normally you could just get the meter probes onto the fins that the breaker clips onto. Failing that, you could probe somewhere else in the box where both phases are available (you could even probe on another adjacent breaker which has both phases, if it's not a circuit that is drawing current). Please be careful. If you're not comfortable with it, don't do it. It's pretty easy to touch a hot.

 

[Kirby64]

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.

You're right, that's a ton of voltage drop for 8A only. Sounds like undersized/overly long wiring.

Also, if ground is missing completely won't the charger throw an error and not let you charge at all? I thought a ground is mandatory.

 

[PatsFan]

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).

Strange thing is this mobile connector works well with no issues 5-15 adapter which is can be hooked to regular 110 volts outlet. I get about 12Amp

 

[PatsFan]

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.

Ground is hooked up correctly see this pic

 

[AlanSubie4Life]

Strange thing is this mobile connector works well with no issues 5-15 adapter which is can be hooked to regular 110 volts outlet. I get about 12Amp

Yes, but the UMC is looking for voltage drop. It may not like seeing 4V of voltage drop when it draws 8A on a 240V circuit. I don't know what the threshold is. Another 120V 15A outlet may not have the same drop, or there may be allowances that say for a 120V circuit it will allow more drop, simply because overall power dissipation will be lower for a lower voltage, lower current circuit (it's I*V or I^2*R). (Again, I don't know what voltage drop is allowed by the UMC and/or the vehicle.)

It could be the adapter - after all, the UMC is saying that there is a problem with the adapter, according to the UMC manual.

Maybe just swap it out with Tesla at this point to see if it fixes the problem. Can always revisit this problem again if you have the same problem.

However, if you want to continue to investigate at home now:

Follow up on those other things listed above. The motivation for that list: As far as I can tell, based on various pictures you've posted:

When drawing 8A, you measure 242V at the breaker outlet.

Your other picture (just posted) shows that at the OUTLET when drawing 8A, you also have 242V.

I'm making a lot of assumptions here. But that's the picture I have in mind with some assumptions.
So that says to me you have negligible voltage drop on the wires between the breaker and the outlet. And you have 4V drop through the wiring (service connection/bus bars/etc.) before the breaker, and/or through the breaker itself, when drawing 8A.

That seems like a lot. If it's the breaker, and it really has 4V drop across it, it's dissipating 32W, and would start to feel warm quite rapidly.

If it's something else, it may be normal and ok, but still seems like a lot to me.

 

[eprosenx]

All of the advice above is solid to me.

I would also check to make sure that the insulation of the wire where it is shoved into the receptacle is stripped back sufficiently far and not shoved into the terminal of the receptacle and caught under the lug. I have seen this twice recently and in one case it nearly burned down a friends house. Make sure the terminals are tight as well (also check the same thing at the breaker end).

Edit: I just realized it is saying "check adapter". And limiting you to 8a. I have never seen a 8a limit before (I have seen 16a limit when the UMC is not properly locked into the car charge port). I have also seen it back down 25% on speed when it sees too much voltage drop. Those I think also generate different error messages.

So this sounds like maybe the UMC to the wall adapter is the issue. I assume you have re-seated that, checked the plug and receptacle end of that on the UMC for debris? It also would be interesting to use the multimeter to measure the resistance of the resistor in it (which indicates to the UMC what adapter is connected). But I don't know which pins you need to measure between and what resistance values you are looking for.... (I supposed I could go home and play around a bit and generate a table of them since I own all eight)

 

[AlanSubie4Life]

@PatsFan Sorry, I went back to this this evening, and realized I got really confused on this one because there are multiple pictures.

I'm going to rephrase what I said in my last post, and to some extent take back my prior post (however, my list of "things to do" stands - and my suggestion to just go ahead and swap out the adapter with Tesla really quickly if that's something you can do). Also check those connections at the socket as @eprosenx says.

Actual situation/voltages we have seen, from your pictures (I'm not going to bother to link to them all, but they are all in this thread), ALL measured with your voltmeter:
246V -> Open Circuit Voltage, measured at the plug
242V -> At the output side of the breaker (PRESUMABLY when you are drawing 8A - this is unknown to us)
238V -> At the plug, when you are drawing 8A (previously I had stated this was 242V, but it looks like that was a reduced load condition??? - you have another picture showing 242V with the UMC plugged in - that's how I got confused) In any case, the minimum voltage I have seen you picture is 238V at the plug.

Measured by the car:
244V @ 8A -> This is a different measurement device, so it's not clear we can directly compare to above. And we shouldn't. It's just a datapoint. I think we should only compare car measurements to other car measurements at different currents.

So, with assumption that meter measurements are correct relative to one another AND I am making the correct assumptions about the load conditions, you have:
- at least 3.3% (8/246) drop @ 8A, from service inlet to socket. (since open circuit is 246V and 238V is measured under load)
- about half of that drop (1.6% of 246V) is in the wire between breaker & socket. (What is the run length of this 8AWG wire?)

Frankly, it all seems a bit odd to me (generally higher losses than I would expect). It's not what I would expect, though it's possible this is just due to confusion in the posts and incorrect assumptions about the pictures you've posted.

I went to this calculator, and I find that to have a total of 4V drop on the 8AWG wire at 8A, you would need to have a 300ft (one way!) run!!! How long is your run?

electrician2.com voltage drop calculator

So that seems...weird. So as @eprosenx says, voltage can fluctuate from the utility, so you probably have to take all the measurements at the same time to be sure they're consistent. It also would depend on whether you're running a clothes dryer or oven in the house, etc., because that will somewhat alter the line voltages everything in the house sees.

Anyway, something seems odd. Unless that's your run length.

I sure hope it's the adapter at this point. Then we can ignore all the data and hopefully all is well.

 

[PatsFan]

@PatsFan Sorry, I went back to this this evening, and realized I got really confused on this one because there are multiple pictures.

I'm going to rephrase what I said in my last post, and to some extent take back my prior post (however, my list of "things to do" stands - and my suggestion to just go ahead and swap out the adapter with Tesla really quickly if that's something you can do). Also check those connections at the socket as @eprosenx says.

Actual situation/voltages we have seen, from your pictures (I'm not going to bother to link to them all, but they are all in this thread), ALL measured with your voltmeter:
246V -> Open Circuit Voltage, measured at the plug
242V -> At the output side of the breaker (PRESUMABLY when you are drawing 8A - this is unknown to us)
238V -> At the plug, when you are drawing 8A (previously I had stated this was 242V, but it looks like that was a reduced load condition??? - you have another picture showing 242V with the UMC plugged in - that's how I got confused) In any case, the minimum voltage I have seen you picture is 238V at the plug.

Measured by the car:
244V @ 8A -> This is a different measurement device, so it's not clear we can directly compare to above. And we shouldn't. It's just a datapoint. I think we should only compare car measurements to other car measurements at different currents.

So, with assumption that meter measurements are correct relative to one another AND I am making the correct assumptions about the load conditions, you have:
- at least 3.3% (8/246) drop @ 8A, from service inlet to socket. (since open circuit is 246V and 238V is measured under load)
- about half of that drop (1.6% of 246V) is in the wire between breaker & socket. (What is the run length of this 8AWG wire?)

Frankly, it all seems a bit odd to me (generally higher losses than I would expect). It's not what I would expect, though it's possible this is just due to confusion in the posts and incorrect assumptions about the pictures you've posted.

I went to this calculator, and I find that to have a total of 4V drop on the 8AWG wire at 8A, you would need to have a 300ft (one way!) run!!! How long is your run?

electrician2.com voltage drop calculator

So that seems...weird. So as @eprosenx says, voltage can fluctuate from the utility, so you probably have to take all the measurements at the same time to be sure they're consistent. It also would depend on whether you're running a clothes dryer or oven in the house, etc., because that will somewhat alter the line voltages everything in the house sees.

Anyway, something seems odd. Unless that's your run length.

sure hope it's the adapter at this point. Then we can ignore all the data and hopefully all is well.

My run length is about 50ft from basement to garage. But I am not sure if outlet or line is the issue here. If I use a Chargepoint EVSE on this same outlet which requires 40A breaker, that EVSE works fine and car charges at 32Amp. But I really want to ditch this chargepoint EVSE because it’s very pricey $600 and just for delivering 32A which Tesla mobile connector can do as well. I don’t have extra usage through this chargepoint EVSE. Below is the EVSE I have right now which I want to return

https://www.amazon.com/gp/product/B071CV8KVK/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

[AlanSubie4Life]

My run length is about 50ft from basement to garage. But I am not sure if outlet or line is the issue here. If I use a Chargepoint EVSE on this same outlet which requires 40A breaker, that EVSE works fine and car charges at 32Amp. But I really want to ditch this chargepoint EVSE because it’s very pricey $600 and just for delivering 32A which Tesla mobile connector can do as well. I don’t have extra usage through this chargepoint EVSE. Below is the EVSE I have right now which I want to return

https://www.amazon.com/gp/product/B071CV8KVK/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

@PatsFan, well, as an additional experiment, then, for science :

1) Plug in that Chargepoint EVSE, get the car charging at 32A. (Make sure it fully ramps to 32A)

2) Measure the voltage at the socket as you did before, while drawing 32A. (Also take a picture of what the car says/measures!)

3) Measure the voltage at the breaker, while drawing 32A, as you did before.

If those voltages all look "normal" (I would say less than 5% reduction from line voltage at the plug would make me feel ok - but there's probably an actual spec), then probably it's just the adapter (as the UMC is telling you). Maybe the adapter is just defective and the resistor or the contacts which set the charge level are no good, as @eprosenx suggested - check the contacts on where it plugs into the UMC and make sure there's not some junk in the contacts or something (I haven't ever examined the connection closely so not sure what it looks like). There's a first time for everything.

 

[ChrisH]

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

So eventhough my LR CAN draw 48A I’m still okay because the gen 2 UMC maxes out at 32? I also set it to draw 30 in the charging screen in the car (figured this would be even slightly more safe?)

 

[AltLogic]

Wait a second. That picture shows a bare wire (I’ll call that ground) a black wire (I’ll call that hot) and a white wire (I’ll call that neutral, wait it’s 240 v so it must be hot). I would willing to bet money that the entire run is not the same gauge wire and the Tesla UMC correctly reduces the amperage for safety reasons. The previous EVSE wasn’t so protective.

 

[PatsFan]

Wait a second. That picture shows a bare wire (I’ll call that ground) a black wire (I’ll call that hot) and a white wire (I’ll call that neutral, wait it’s 240 v so it must be hot). I would willing to bet money that the entire run is not the same gauge wire and the Tesla UMC correctly reduces the amperage for safety reasons. The previous EVSE wasn’t so protective.

How much money you wanna bet that it’s not same gauge lol . It’s 8-3 gauge all through

 

[AltLogic]

How much money you wanna bet that it’s not same gauge lol . It’s 8-3 gauge all through

It is tempting to bet a large sum it isn’t 8-3. But I’ll pass.

 

[AlanSubie4Life]

Wait a second. That picture shows a bare wire (I’ll call that ground) a black wire (I’ll call that hot) and a white wire (I’ll call that neutral, wait it’s 240 v so it must be hot).

It is two hots 180 degrees out of phase. Standard stuff. And the ground is not current carrying (except in case of fault), so it does not have to be as large. I think based on all pictures so far (there are pictures at the breaker panel too), all looks good on that front.

 

[AlanSubie4Life]

How much money you wanna bet that it’s not same gauge lol . It’s 8-3 gauge all through

Technically 8-2 unless there is another conductor hidden. But 8 gauge is the relevant issue here. Which it is. You don’t need 8-3.

 

[eprosenx]

Technically 8-2 unless there is another conductor hidden. But 8 gauge is the relevant issue here. Which it is. You don’t need 8-3.

Also, it is presumably THHN in conduit so it is not 8-2 or 8-3. It is just two 8 gauge copper THHN wires in conduit along with like a #10 bare copper. ;-)

 

[AlanSubie4Life]

Also, it is presumably THHN in conduit so it is not 8-2 or 8-3. It is just two 8 gauge copper THHN wires in conduit along with like a #10 bare copper. ;-)

Touché. I am not an electrician!

 

[AlanSubie4Life]

So eventhough my LR CAN draw 48A I’m still okay because the gen 2 UMC maxes out at 32? I also set it to draw 30 in the charging screen in the car (figured this would be even slightly more safe?)

Reply from @eprosenx above:

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.

The Gen2 UMC will not draw more than 32A (it tells the car it can't provide more than that) so you should be fine. Furthermore you have a 40A breaker so that will provide some protection if something goes wrong. And code compliant according to @eprosenx as he has explained.

You don't need to limit the car to 30A, or set any limit in the car, but no harm in doing so, and I guess marginally safer to charge at lower currents, if you don't need the speed. Just slightly more margin to failure if something goes wrong. But no need for a limit.

 

[PatsFan]

I gave up on all experiments and readings, I’m using Chargepoint EVSE for now on same outlet until Tesla sends me a replacement adapter.

 

[eprosenx]

I gave up on all experiments and readings, I’m using Chargepoint EVSE for now on same outlet until Tesla sends me a replacement adapter.

View attachment 359232

Thanks for posting that one last screenshot.

This tells me you for sure do not have a voltage issue. 242 volts under 32 amps of load is perfect.

I am pretty confident you don’t have a wiring issue.