Installing a Nema 14-50 on a 30 Amp Breaker

[Alketi]

When I decided to get the Tesla and sell the Prius, I was hoping to upgrade the subpanel to 100a rather than 50a, and upgrade that breaker to 60a rather than 30. Then I could put in a NEMA 14-50 and charge at the full 48a.
I believe I asked on here months ago what the supply to the subpanel was based on the wire used. The answer I got back was it looked like blah-blah-blah and could take well over 100a at 240v. I'll attach a picture of the plug from the L2 Levitron charger. It required a mated socket. Based on the orange covering for the 2' piece from the outlet to the breaker I deduced the entire circuit was now limited to 30a. right?

I would have preferred he use a 50a breaker and wire that to the NEMA 6-50 plug and then I could plug in a 30a load... That's the second screw up that electrician made. That and wiring my tower to the service ground.

As far as the L2 charger goes...it was UL approved.

@wcorey best thing would be to put a label on your outlet as "30A max", so anyone coming after you is aware of the situation.

It might be possible to fish #6 wire through your short wall run, rather than break the drywall. But, if your subpanel is only 60A, then it's probably a moot point.

 

[wcorey]

@wcorey Well, he's talking about just the adapter piece that fits in your hand. That's just a pass-through with no smarts. But the point with J1772 is that the station itself that has the J1772 handle on it supplies a carrier signal that announces what the maximum amps are. So whatever type and rating of station it is will send a signal saying if it's 30A available or 24A available, etc. So any cars that plug into it get that pilot signal to tell them how much they are allowed to draw.

Ah! That I did not know so the Levitron L2 charger passes the current information thru it's J1772 handle through the adapter to the car. This is why the initial time I charged the car after arriving from the delivery, the car immediately said, as the screen became active, 32a 22mph charging rate. I thought it was all part of the inverter software. Thanks Rocky.

So next question, what would happen if I bought a 6-50 adapter from Tesla and plugged the UMC into the outlet directly? Let's further stipulate I left the car's charging screen set to auto.

 

[Alketi]

So next question, what would happen if I bought a 6-50 adapter from Tesla and plugged the UMC into the outlet directly? Let's further stipulate I left the car's charging screen set to auto.

The car will attempt to draw 40A (80% of rated capacity).

Your 30A breaker may or may not trip.

If the breaker doesn't trip, the wires will heat up and at some point the car will sense the unusual voltage drop and stop charging with a fault detected.

If both of those fail, you'll have a fire in your wall.

 

[wcorey]

@wcorey best thing would be to put a label on your outlet as "30A max", so anyone coming after you is aware of the situation.

It might be possible to fish #6 wire through your short wall run, rather than break the drywall. But, if your subpanel is only 60A, then it's probably a moot point.

Can you tell by the feed to the subpanel what that run could take? I believe it's only 40' from the main service to the subpanel. If it could, in fact, take say 75a I'd rather change the breakers on the main to that, and drop a 60a circuit to a NEMA 14-50 and put in a Tesla Charger with a 14-50 plug or simply wire a normal charger from it and be able to charge at the full 48a. That's if I had several hundred dollars burning a hole in my wallet. Charging at 22miles/hr of charge is fine. More is better though. The panel is mounted to a stud. The orange wire enters the top left so I believe it has to go through a hole drilled in the stud. It goes down the height of the subpanel and across the width between studs to where the 6-50 outlet is. So that wire may actually traverse two studs. Prudence would let sleeping dogs lie. When I leave this house it'll likely be feet first. It would be easier to shut off the line at the breaker. Or magic marker.
The 75 is for the garage doors and garbage disposal. Without requesting the garage subpanel as they were building the house everything would have been on one 15a line from the main panel.

 

[wcorey]

The car will attempt to draw 40A (80% of rated capacity).

Your 30A breaker may or may not trip.

If the breaker doesn't trip, the wires will heat up and at some point the car will sense the unusual voltage drop and stop charging with a fault detected.

If both of those fail, you'll have a fire in your wall.

Thanks! so again, easiest thing is do nothing and use the existing Levitron L2 charger.

 

[davewill]

... When I leave this house it'll likely be feet first. ...

Which could be tomorrow. There are no guarantees.

 

[wcorey]

Which could be tomorrow. There are no guarantees.

Darn...I put in for an 85 yr warranty. If that were to happen I suspect my wife would sell her Prius, use the Model 3 and life would go on. Yes, I know... If someone were to say given the proximity of the outlet to the subpanel the most expensive part of the cost to swap the #8AWG (orange jacket) is getting the drywall guy to show up at all. I'd do it next week. There were a number of mistakes that electrician made. I'd be surprised if he were still licensed.

 

[Alketi]

Can you tell by the feed to the subpanel what that run could take?

Sorry, I can't tell by looking at just the wires.

 

[LCR1]

......Then I could put in a NEMA 14-50 and charge at the full 48a..........

No you couldn't because the 14-50 is still rated at 40amps max continuous load. You'd also need the wall charger to get 48A, the mobile one won't do it. The only way to get 48A is the wall charger directly wired to a 60Amp breaker.

For reference, a continous load is considered a constant load that last more than 2 hours A stove is not considered continuous because the elements cycle on and off once it gets to temp. Really, there aren't many things in your home that are continuous

 

[wcorey]

No you couldn't because the 14-50 is still rated at 40amps max continuous load. You'd also need the wall charger to get 48A, the mobile one won't do it. The only way to get 48A is the wall charger directly wired to a 60Amp breaker.

Thank you!

 

[wcorey]

Sorry, I can't tell by looking at just the wires.

Fair enough, I was hoping the color coding would be relevant.

 

[Rocky_H]

So next question, what would happen if I bought a 6-50 adapter from Tesla and plugged the UMC into the outlet directly? Let's further stipulate I left the car's charging screen set to auto.

The car will attempt to draw 40A (80% of rated capacity).

No, not 40A, because this is a thread about a Model 3. The newer 2nd generation mobile charge cords started shipping with the Model 3 in late 2017, and by the beginning of 2018, all of the Model S and X vehicles were coming with them too. Those new cords can only do a maximum of 32A. But I do have a 2014 S and it does have the older cord that can do 40A maximum.

So @wcorey , where the J1772 stations generate that pilot signal to announce the amp limit, the Tesla charge cord does a cute little work-around to generate that same kind of signal. The different plug adapters that can be attached to the mobile charge cord have different value resistors inside them. When the cord is plugged in, it can read and identify what type of adapter plug is attached to it as a method of identifying the outlet. So if you have the 5-15 adapter on, the cord "knows" 15A outlet and will only allow max 12A draw. If you have the 14-30 plug attached, it will "know" 30A circuit, and only allow 24A max.

This all works fine as long as each step in the chain is being done properly, by using the right matched plug adapter that plugs directly into that same kind of properly installed outlet. It's when things go outside of the box with plugging into other external pigtail adapters to convert to plug into some other type of outlet or an outlet that's on incorrect wiring or breakers that things can be weird and you have to know what you're doing.

The important part, though, is that the official Tesla plug types, though do set the current for the right level of amps for that outlet type, and it is OK if you need to use a pigtail to convert it to a different outlet type of the same number of amps. The car fortunately isn't picky about matching the voltage level of the adapter type. It will detect and use whatever voltage level is there, so it does still work if you need to adapt a 120V type to a 240V type or vice versa.

But this isn't 5 years ago, so there is more support for charging adapters, and you shouldn't need to try to build your own. This site: EVSEAdapters.com sells very professionally built adapters for the Tesla charging cable that do have that internal resistor that sets the current correctly. So if there's some outlet at a place you need to use, and Tesla doesn't sell a plug for it, I would recommend to just buy it from these guys.
Tesla Model S / X / 3 Gen 2 Charging Adapters

 

[Alketi]

@Rocky_H You're right. The mobile charger on the Model 3 will try to draw 32A on (in this case) 30A rated equipment.

Which is even less likely to trip the breaker (I can tell you this from first-hand experience).

And, very likely, since 30A wiring is only rated for 24A continuous, the wires will begin to heat and the car charging will interrupt with a charge fault when the voltage drops below some threshold.

 

[jerry33]

@Rocky_H You're right. The mobile charger on the Model 3 will try to draw 32A on (in this case) 30A rated equipment.

Which is even less likely to trip the breaker (I can tell you this from first-hand experience).

And, very likely, since 30A wiring is only rated for 24A continuous, the wires will begin to heat and the car charging will interrupt with a charge fault when the voltage drops below some threshold.

Very likely, but I wouldn't want to have that as my only safety control. Receptacle, wiring, and breaker all need to match.

 

[wcorey]

No, not 40A, because this is a thread about a Model 3. The newer 2nd generation mobile charge cords started shipping with the Model 3 in late 2017, and by the beginning of 2018, all of the Model S and X vehicles were coming with them too. Those new cords can only do a maximum of 32A. But I do have a 2014 S and it does have the older cord that can do 40A maximum.

So @wcorey , where the J1772 stations generate that pilot signal to announce the amp limit, the Tesla charge cord does a cute little work-around to generate that same kind of signal. The different plug adapters that can be attached to the mobile charge cord have different value resistors inside them. When the cord is plugged in, it can read and identify what type of adapter plug is attached to it as a method of identifying the outlet. So if you have the 5-15 adapter on, the cord "knows" 15A outlet and will only allow max 12A draw. If you have the 14-30 plug attached, it will "know" 30A circuit, and only allow 24A max.

This all works fine as long as each step in the chain is being done properly, by using the right matched plug adapter that plugs directly into that same kind of properly installed outlet. It's when things go outside of the box with plugging into other external pigtail adapters to convert to plug into some other type of outlet or an outlet that's on incorrect wiring or breakers that things can be weird and you have to know what you're doing.

The important part, though, is that the official Tesla plug types, though do set the current for the right level of amps for that outlet type, and it is OK if you need to use a pigtail to convert it to a different outlet type of the same number of amps. The car fortunately isn't picky about matching the voltage level of the adapter type. It will detect and use whatever voltage level is there, so it does still work if you need to adapt a 120V type to a 240V type or vice versa.

But this isn't 5 years ago, so there is more support for charging adapters, and you shouldn't need to try to build your own. This site: EVSEAdapters.com sells very professionally built adapters for the Tesla charging cable that do have that internal resistor that sets the current correctly. So if there's some outlet at a place you need to use, and Tesla doesn't sell a plug for it, I would recommend to just buy it from these guys.
Tesla Model S / X / 3 Gen 2 Charging Adapters

Again Rocky, thank you!

 

[miimura]

Ah! That I did not know so the Levitron L2 charger passes the current information thru it's J1772 handle through the adapter to the car. This is why the initial time I charged the car after arriving from the delivery, the car immediately said, as the screen became active, 32a 22mph charging rate. I thought it was all part of the inverter software. Thanks Rocky.

So next question, what would happen if I bought a 6-50 adapter from Tesla and plugged the UMC into the outlet directly? Let's further stipulate I left the car's charging screen set to auto.

The safest thing in your situation is to continue to use the Leviton EVSE with the Tesla J1772 adapter.

If you purchased the 6-50 adapter for the Gen2 Tesla Mobile Connector provided with a Model 3, the car would try to draw 32A just like if you used the 14-50 adapter provided with the car. Those two adapters are coded to 32A even though the outlets would allow 40A continuous draw. A Gen1 Tesla Mobile Connector with 6-50 or 14-50 adapter and a Corded Mobile Connector (fixed 14-50 plug) will allow the car to draw the full 40A. The other safe and proper thing you could do is buy a Tesla Wall Connector and set it to match the breaker and wire already installed in your wall.

 

[wcorey]

The safest thing in your situation is to continue to use the Leviton EVSE with the Tesla J1772 adapter.

If you purchased the 6-50 adapter for the Gen2 Tesla Mobile Connector provided with a Model 3, the car would try to draw 32A just like if you used the 14-50 adapter provided with the car. Those two adapters are coded to 32A even though the outlets would allow 40A continuous draw. A Gen1 Tesla Mobile Connector with 6-50 or 14-50 adapter and a Corded Mobile Connector (fixed 14-50 plug) will allow the car to draw the full 40A. The other safe and proper thing you could do is buy a Tesla Wall Connector and set it to match the breaker and wire already installed in your wall.

I completely agree with that. There is something to be said for facilitating the car to charge at its most rapid pace, but I think to do that would be more expense than I want to make right now.

 

[M3BlueGeorgia]

The car has no way of knowing what size breaker it's plugged into, it most certainly will pull more than 24A if you use a 14-50 plug

Guys, I was proposing (strongly) going to 14-30 instead of 14-50.

 

[garth_angst]

I am a pretty smart guy, but a moron when it comes to electricity. I have been following this thread and my head spins. I didn't know if I should start my own thread because my question is a little different, but I'll try here.

I am having an electrician run a 240v line from my breaker to the garage where I will put in a NEMA 14-50 outlet. I haven't decided on whether I'll get the SR+ or the LR. I can see that I have a 30 and a 20 amp free on my breaker next to each other. Would I be ok with 50 amps if I were going to get the LR model 3 or do I need 60 as recommended by Tesla? Or is that just if I were using their Wall Charger? If I use 50, does that just mean that I will get a slower charge on the LR or is there a chance for all the bad things I read here?

Remember, I'm a moron, I might not understand if you belittle me for not understanding.

 

[M3BlueGeorgia]

I am a pretty smart guy, but a moron when it comes to electricity. I have been following this thread and my head spins. I didn't know if I should start my own thread because my question is a little different, but I'll try here.

I am having an electrician run a 240v line from my breaker to the garage where I will put in a NEMA 14-50 outlet. I haven't decided on whether I'll get the SR+ or the LR. I can see that I have a 30 and a 20 amp free on my breaker next to each other. Would I be ok with 50 amps if I were going to get the LR model 3 or do I need 60 as recommended by Tesla? Or is that just if I were using their Wall Charger? If I use 50, does that just mean that I will get a slower charge on the LR or is there a chance for all the bad things I read here?

Remember, I'm a moron, I might not understand if you belittle me for not understanding.

A 14-50 socket implies that the wire from the breaker to the socket is rated at 240V/50A (or better) and that you have a 240v/50A breaker.