Installing a Nema 14-50 on a 30 Amp Breaker

[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

That's the whole point of making sure everything is consistent. If the socket, which in this case should be 14-30, matches the gauge of the wire and also matches the breaker, everything "just works".
The 14-30 adapter from Tesla will then prevent the car drawing more than 24A continuous.

 

[eprosenx]

Not looking to hijack this thread, but my situation is very similar (in fact I signed up for this forum to ask similar questions here)...

I had an electrician come to install a 14-50 outlet for charging in my garage with the intent to install a 50 amp breaker, however the guy that came to install looked at the 14-50 mobile adapter and there was something written on it that said 30 amp (can't remember the exact print and I'm not at home to look now) and so he insisted to me that a 30 amp breaker needed to be installed (even though I pulled up the installation PDF for him from the Tesla site). What he did was install the 14-50 outlet and the correct gauge wire that can handle a 50 amp breaker, but used a 30 amp breaker in the box (so presumably my dangers are more limited than the OP here but the heat in a 30 amp breaker getting 32 amps through is a concern). I can confirm that my Tesla phone app has said it's pulling the full 32 amps and the breaker never tripped during 2 charging cycles (about 4.5 hours each). It did get hot but not nearly hot enough to start a fire (not exactly something that puts my mind at ease but I wanted to provide that anecdotal information). I was going to change the breaker out myself but I'll be reaching back out to the electrician mostly to ensure that this guy isn't making this mistake on future customers who might not catch the mistake like I did.

Questions I'm hoping someone can answer for me:

• After 2 charging cycles, is there any chance that there's any damage/concern I should have on my battery or anything problematic with my car? I've noticed after the 2nd charge that my regenerative breaking has been limited but the temp has been dropping into the 40's here in Texas so I am hoping that these two issues are unrelated
• If I have the standard range plus model 3, should I be using a 40 or 50 amp breaker? The 14-50 installation guide on the Tesla site says 50 but the onboard charging information page says 40 (see links below)

This shows 40 amp
Onboard Charger

This shows 50 amp
https://www.tesla.com/sites/default.../NEMA_14-50_installation_guide_NA_US_2017.pdf

If everything is as described, there is zero danger here. Your car won’t be damaged. What likely will happen is that breaker will nuisance trip. As others have stated, it is only rated to 24 amps continuous. Turn your charge rate down to 24 amps if you want to charge successfully prior to getting this fixed.

Your electrician made a big mistake... Yes, it says 30a on the UMC (even though it draws 32a - there are other threads on this forum by me about this), but that is continuous load, so it at least requires a 40a breaker.

So I would definitely swap that breaker for a 50a assuming the wire is 6awg.

Welcome to Tesla ownership!

 

[RaeW]

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

True, the car does not know what breaker it is plugged into; however, the car is set for 24 amps and for 3.5 years it has never drawn anything more than 24 amps (this appears on the screen while charging). The car does know what plug is engaged though, so with the 14-50 plug the car shows it is drawing 24/40 amps (40 = 80% of 50). Should the setting fail, the car cannot draw more than 40 amps and the breaker (tested) trips at 28 amps. Based on Community response, I have decided to change the socket to a 14-30 and have ordered the 14-30 adapter. This will create a 24/30 draw on the 30 amp breaker which will still trip at 28 amps. It won't make any difference in performance, but the socket will now be the correct one for the line.

 

[RaeW]

You can use either a 40a or 50a circuit successfully with the mobile connector. 50a is preferred since you have the capacity and the wiring is done correctly for that. For some bizarre reason, Tesla printed "30a" on the 14-50 adapter itself, however the setup draws 32a by design. You need to have that electrician change the breaker to 50a. Have him call Tesla if that's what it takes to convince him. A 30a breaker will not cut it and you shouldn't use the plug until it's fixed (or a least turn the amperage in the car down to 24 until it's changed).

My 14-50 adapter from 2015 shows 50 AMPS, 208-240V.

 

[RaeW]

What if someone moves into your house later on and it burns down because they didn't know about your mis-wired plug? People could DIE.

What part of my post did you not understand?
Based on Community response, I have decided to change the socket to a 14-30 and have ordered the 14-30 adapter.

 

[StellarRat]

What part of my post did you not understand?
Based on Community response, I have decided to change the socket to a 14-30 and have ordered the 14-30 adapter.

I deleted it. Sorry.

 

[davewill]

My 14-50 adapter from 2015 shows 50 AMPS, 208-240V.

I should have specified the NEWER mobile connectors that are shipping now deliver 32a max and can run on 40a. The older ones delivered 40a and needed a 50a circuit.

 

[wcorey]

And, you meant NEMA 14-50, not 15-40.

And the answer is still no.

(The reason is -- you cannot put a higher current outlet on a lower current breaker with lower current wiring, and then "try" to use it carefully. It's both illegal and obviously dangerous, unless you don't mind burning your house down.)

I bought a Leviton L2 Charger for my, then, Prius Plugin Adv. The Leviton charger has a J1772 plug and a NEMA 6-50 plug requiring a 30a feed as opposed to the max rated 50a feed. The electrician the builder hired argued with me that (6-50 outlet) required a 50a source,until I showed him the Leviton installation. He put it on a 30a circuit. I wish he had put in a 30a circuit with a 2' stretch of electrical cable capable of taking 50a as then I'd have swapped the outlet to a 14-50 with a 50a breaker. But, at 30a I generally get 22m/hr of charge as that 30a circuit delivers only a continuous 24a to the car. A 50a circuit would deliver a constant 40a to the car, pretty near the car's AC limit of 48a from a 60a circuit. To change that now would require cutting out dry wall to replace that 30a (orange) cable from the breaker to the outlet.

I am not an electrician but your comment makes no sense to me. I have a 30a load on a 50a capable outlet on a 30a circuit with a 30a rated wiring. You said, a higher current outlet on a lower current breaker. I suspect you were thinking running a 50a load through a 30a wire? Yes, that would burn the house down. I use a second J1772 adapter for my M3 just fine. In that way away from home if I need a charge from a J1772 source I have the adapter in my UMC bag. One difference I guess is I still use the Leviton L2 charger with the J1772 -> Tesla adapter on the end. At 22 m/hr an overnight charge would give one approximately 220 mile capacity from a 30a source.

 

[RaeW]

I am not an electrician but your comment makes no sense to me. I have a 30a load on a 50a capable outlet on a 30a circuit with a 30a rated wiring. You said, a higher current outlet on a lower current breaker. I suspect you were thinking running a 50a load through a 30a wire? Yes, that would burn the house down. I use a second J1772 adapter for my M3 just fine.[/QUOTE]

wcorey:
There's a lot of misinformation/misinterpretation here, but the responder's (Alketi) intention was related to the socket. Using a 14-50 socket on a 30A breaker is not technically correct, but is not hazardous if the draw is only 24 A. The car will recognize the 50A socket and automatically set the draw to 80% (i.e. 40A). The car can then be manually set to 24A and everything is fine in that setup (should the manual setting fail, the car will try to draw 40A and the breaker should trip). Technically correct installation is a 14-30 socket which the car will recognize and automatically set the draw at 24A, which is appropriate for the breaker. This "burn the house down" business assumes the 30A breaker does not do its job!

 

[LCR1]

That's the whole point of making sure everything is consistent. If the socket, which in this case should be 14-30, matches the gauge of the wire and also matches the breaker, everything "just works".
The 14-30 adapter from Tesla will then prevent the car drawing more than 24A continuous.

Except that's not what you said. You said the car won't draw more than 24 on a 30, and that's absolutely false. The car will pull however much it want's to regardless of what size circuit it's hooked up to. You can plug the cord into a 14-50 on a 40amp circuit and it will most certainly draw 100% of those 40amps.

The car won't draw more than 24A on a 30A circuit ... because one should never draw more than 80% continuous and the car knows the rules.

So you'll be fine.

Again, you won't be fine because the car will draw however much it was told to draw regardless of the actual size of the circuit.

True, the car does not know what breaker it is plugged into; however, the car is set for 24 amps and for 3.5 years it has never drawn anything more than 24 amps (this appears on the screen while charging). The car does know what plug is engaged though, so with the 14-50 plug the car shows it is drawing 24/40 amps (40 = 80% of 50). Should the setting fail, the car cannot draw more than 40 amps and the breaker (tested) trips at 28 amps. Based on Community response, I have decided to change the socket to a 14-30 and have ordered the 14-30 adapter. This will create a 24/30 draw on the 30 amp breaker which will still trip at 28 amps. It won't make any difference in performance, but the socket will now be the correct one for the line.

The car setting can certainly change on it's own, there have been times where It's gone between 30 and 40 amps without me touching it, doesn't matter with my set up but don't depend on it. And I was quoting someone who said the car seemd to know the difference when it actually doesn't. I've also had people at the service center clueless tell me the car knows the size of the circuit it was hooked up to.

 

[Vines]

Just saw a Square D Breaker come off a busbar, the breaker totally failed and never tripped, though one of its legs was shorting out and causing the PV to drop in and out. Rather than trip, this breaker fractured, freezing the trip unit.

When removed, the stab connection stayed on the bus, and the rest of the breaker broke off.

Breakers should never be the only line of defense against overload issues. They may work great 10 times, then fail the 11th. They may fail the first time they are overloaded. This is why its bad to use a plug in receptacle like a 14-50 without the proper wire.

As to the 32A draw on the 14-50 outlet, with properly sized 50A wire, but a 30A breaker. I'd recommend that you change this out to a 50A breaker. In the meantime, set your charge rate in the car to 24A. Its not a good idea to pass more amps through a breaker than its designed to take. At best its a nuisance trip, at worst the higher 32A rate damages the breaker to where its not able to trip. Breakers are thermal devices, so what works now in winter may start tripping as summer comes around and you really don't want to be tripping the breaker a bunch of times unnecessarily.

 

[eprosenx]

My apologies for being a little pedantic here, but I wanted to jump into the discussion about receptacle sizing with some actual relevant code snippets.

My understanding of the code is that technically you can install a larger rated receptacle on a smaller rated circuit as long as the intended load to be connected to it does not exceed the rating of the circuit.

So if you had an EVSE that somehow had a 14-50 (or 6-50) plug on it but that only drew a max of 24a continuous, you could technically put that on a 30a circuit with a 14-50 receptacle (though I don't think UL would allow a device like that to exist? - I am not sure). See 210.21(B)(1) below.

Anyway, I am being pedantic here because while technically 2017 NEC might allow it, I can not think of a situation I would recommend someone do it.

Note that in the situation we are talking about here, a Tesla UMC draws 40a continuous (Gen 1), or 32a continuous (Gen 2) when the 14-50 or 6-50 adapter end is used. Only if you use the 14-30 or 10-30 adapter can you then calculate it as if it is a 24a continuous load.

 

[jerry33]

My apologies for being a little pedantic here, but I wanted to jump into the discussion about receptacle sizing with some actual relevant code snippets.

My understanding of the code is that technically you can install a larger rated receptacle on a smaller rated circuit as long as the intended load to be connected to it does not exceed the rating of the circuit.

So if you had an EVSE that somehow had a 14-50 (or 6-50) plug on it but that only drew a max of 24a continuous, you could technically put that on a 30a circuit with a 14-50 receptacle (though I don't think UL would allow a device like that to exist? - I am not sure). See 210.21(B)

There are two issues with this. First, and most important, is that you have to check the amp setting on the car every single time you charge without exception. The second is that although the code may allow it, the inspector may not. This varies by city.

The only safe thing to do is to use the proper wire for the breaker size, and the receptacle type should match the breaker. The proper wire size can vary depending upon the length of the run.

 

[Alketi]

I bought a Leviton L2 Charger for my, then, Prius Plugin Adv. The Leviton charger has a J1772 plug and a NEMA 6-50 plug requiring a 30a feed as opposed to the max rated 50a feed. The electrician the builder hired argued with me that (6-50 outlet) required a 50a source,until I showed him the Leviton installation. He put it on a 30a circuit. I wish he had put in a 30a circuit with a 2' stretch of electrical cable capable of taking 50a as then I'd have swapped the outlet to a 14-50 with a 50a breaker. But, at 30a I generally get 22m/hr of charge as that 30a circuit delivers only a continuous 24a to the car. A 50a circuit would deliver a constant 40a to the car, pretty near the car's AC limit of 48a from a 60a circuit. To change that now would require cutting out dry wall to replace that 30a (orange) cable from the breaker to the outlet.

I am not an electrician but your comment makes no sense to me. I have a 30a load on a 50a capable outlet on a 30a circuit with a 30a rated wiring. .

@wcorey, I don't see how what you're doing is technically legal.

Yes, for the moment you're safe if you "carefully" use the 50A rated outlet with 30A wiring at only 30A. However, what happens if you're not home and someone else plugs in a 50A device into that outlet? What happens when you sell the house?

What you're doing is the equivalent of using a regular 15A 120V outlet and putting 5A wiring with a 5A breaker behind it and saying you're only going to plug in a lamp so you're fine.

That's the reason this is against code.

(Cutting the drywall isn't that big of a deal. And with how short the wire is, it might not cost you much to upgrade to 50A)

 

[wcorey]

I, honestly, am not trying to hijack the conversation.
At the end of the day if you are drawing more current than the house wiring can pass you run the risk of a house fire, independent of what outlet you use, right?
This is an excellent opportunity for those of you with EE degrees or PEs to shine.

Can we all back up a bit? I believe people are referring to outlets (sockets) as plugs and visa versa.
I consider a socket == receptacle == outlet to be the female side of the connection and a plug to be the male mate. Right?
A plug is inserted into the car charging outlet. Unless you have a Tesla charger you use an adapter to convert from one source to a compatible plug for the car.

So the issue then is how does the car know what the charging current is? I thought it was software determined. Let's say you do have a Tesla High Speed Wall Charger. There is no NEMA anything. How does the car know, if not via software? The same charger plug can charge a 48a Model 3 or a 72a Model S...correct?

Using the J1772 adapter my M3 tends to charge at 24a from a 30a charge source. I've also seen the car charge at a much lower rate than 24a. Not 100% on that but have seen it charge at 22mph, 11mph and 3mph.
So there is the charging port on the car. How does it have a clue what outlet type is on your garage wall or what amperage that socket is being fed? Again, consider a Tesla Wall Charger.

 

[wcorey]

@wcorey, I don't see how what you're doing is technically legal.

The most direct answer I can give is I don't know. I have more questions now than answers. The larger answer is, I didn't do it, a licensed electrician did it and, presumably, the electrical inspector approved it. This was done during construction of the house before occupancy permit and building/electrical inspector handoff. And before we took occupancy.

 

[LCR1]

I, honestly, am not trying to hijack the conversation.
At the end of the day if you are drawing more current than the house wiring can pass you run the risk of a house fire, independent of what outlet you use, right?
This is an excellent opportunity for those of you with EE degrees or PEs to shine.

Can we all back up a bit? I believe people are referring to outlets (sockets) as plugs and visa versa.
I consider a socket == receptacle == outlet to be the female side of the connection and a plug to be the male mate. Right?
A plug is inserted into the car charging outlet. Unless you have a Tesla charger you use an adapter to convert from one source to a compatible plug for the car.

So the issue then is how does the car know what the charging current is? I thought it was software determined. Let's say you do have a Tesla High Speed Wall Charger. There is no NEMA anything. How does the car know, if not via software? The same charger plug can charge a 48a Model 3 or a 72a Model S...correct?

Using the J1772 adapter my M3 tends to charge at 24a from a 30a charge source. I've also seen the car charge at a much lower rate than 24a. Not 100% on that but have seen it charge at 22mph, 11mph and 3mph.
So there is the charging port on the car. How does it have a clue what outlet type is on your garage wall or what amperage that socket is being fed? Again, consider a Tesla Wall Charger.

The car knows based on the plug installed on the EVSE. If you have the 40amp plug from a gen1 EVSE the car will charge at 40amps, it doesn't matter if that wiring or breaker is only rated for 15 amps, you have a 40amp plug end on that EVSE the tesla will assume it can pull 40amps.

The J1772 adapter isn't limited, at least not on the older cars, they allow a full 80 amps.

If you have a wall charger the current is limited but the setting a human manually puts in the box, again, you can manually set it to 80 amps and hook it up to a 15amp breaker and wiring and the car will still try and pull 80 amps.

 

[Rocky_H]

I can confirm that my Tesla phone app has said it's pulling the full 32 amps and the breaker never tripped during 2 charging cycles (about 4.5 hours each). It did get hot but not nearly hot enough to start a fire (not exactly something that puts my mind at ease but I wanted to provide that anecdotal information).

WHYYY? When you knew that it had the wrong 30A breaker, why did you still go ahead and allow it to charge at the full 32A, when you knew that was overloading the circuit? Twice! Why didn't you turn down the amps from the screen in the car?

 

[wcorey]

Yes, for the moment you're safe if you "carefully" use the 50A rated outlet with 30A wiring at only 30A. However, what happens if you're not home and someone else plugs in a 50A device into that outlet? What happens when you sell the house?

What you're doing is the equivalent of using a regular 15A 120V outlet and putting 5A wiring with a 5A breaker behind it and saying you're only going to plug in a lamp so you're fine.

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.

 

[Rocky_H]

The J1772 adapter isn't limited, at least not on the older cars, they allow a full 80 amps.

@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.