Installing a NEMO 14-50 outlet advice

[spdn4cr]

Hi all,

I've moved into a new home and am a first time Tesla owner and noticed that in my garage there is a outlet cover that says "EV Charger". When I took off the cover there are wires beneath it as well as a breaker in my electrical panel that says EV Charger and has 40 on it (which I'm assuming is the amps). I have no electrical background but was hoping to do this on my own. It seems like my garage is prewired for the outlet which I can use for my new Tesla. I was assuming I could just go to my local Home Depot to get a NEMO 14-50 outlet and install it on my own. What scared me is that I've been reading on multiple forums that the charger that comes with the Tesla has been melting or overheating in many people's homes because its pulling a constant 40 amps and the breakers/wires of those using a 40 amp breaker was causing many to have issues.

I've then read that recently Tesla lowered the amount of amps on their chargers to 32 amps max (on the 2nd gen) to alleviate this problem. Does anyone know if this is true, and if so, is it just as easy as me buying a NEMO 14-50 outlet, installing it and plugging in my new car and I should be good to go? Thanks for any advice!

 

[spdn4cr]

I mean NEMA 14-50

 

[boaterva]

First, it’s NEMA. . See my sig for Flasher’s FAQ that should answer all your questions.

But on the face of it, you need a 50 Amp breaker for a NEMA 14-50 outlet.

If you read what you said, it was 100% wrong. It needs a 50 Amp breaker and wires sized for that. 40 Amps is the continuous max load that is proper for that.

The UMC was reduced to 32 Amps to be safer since some were generating heat at 40, but that’s nothing to do with the circuit’s safety. If installed correctly, it should be able to run 40 Amps forever.

 

[spdn4cr]

Got it, thanks boatvera. Is there another NEMA type outlet that I could install that would account for this or do I have to have an electrican change out my breaker? I'm also not sure if the wiring has it's limitations too.

 

[spdn4cr]

I'm also going to check out your FAQ...good stuff. Thanks! It conflicts with other sites I've seen so hopefully yours is right. I've posted this question elsewhere and most people have responded that I could use the NEMA 14-50 on the 40A breaker and it would be fine on the 32A charger but now I'm concerned that's not the case. There's definitely a wealth of information written on this now I just need to figure out whose is correct

 

[Swampgator]

OP,

I have been researching this subject today myself in preparation. I am not an electrician but I have worked (in college) for an electrical contractor and have a general understanding of this subject matter.

#1 at the panel you need a 2-pole 50 amp breaker that matches your panel. Mine is Eaton but just look at your breakers and you will see what you need. May be Square D, etc.
#2 Wire: If you have a run of less than 150 Tesla recommends 6/3 wire. I would play it safe and move to 4 awg wire for runs over 100'. Use 6/3 even for short runs.
#3 Get a nema 14-50 box. Options vary depending on your installation. This is what I am using: https://www.amazon.com/gp/product/B00M3H6494/ref=ox_sc_sfl_title_1ie=UTF8&psc=1&smid=ATVPDKIKX0DER

As for your specific situation: If you can determine the wire gauge in your pre-install and it's 6/3 you are golden. Just upgrade the breaker to a 50 amp (after turning off main power) and you are good to go as long as the outlet accepts 14-50 plug.

If the wire is 8awg then I believe you can still set the car to accept less than the 32 amp (model 3) max. But I am not sure of that so you may want to consult your owners manual.

 

[FlatSix911]

Here is a quick installation guide for a NEMA 14-50 and 14-30 outlet... just check your wire and circuit breaker size.

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

https://www.tesla.com/sites/default.../NEMA_14-30_installation_guide_NA_US_2017.pdf

 

[ewoodrick]

I suspect that the easiest solution is to get the Tesla wall connector. It can be set at whatever limit is safe. Even if you hire an electrician, it should be a relatively easy install. Basically all that has to be done is to mount the device and configure it.

 

[SomeJoe7777]

If you have a 40A breaker, I'm going to assume you have 8 gauge wire. If you do not want to replace this wire, you're in kind of a pickle.

The issue is that the previous owner who used this circuit probably had a permanently installed EVSE rated for a 40A circuit (and therefore supplied 32A or less to the car to comply with the 80% continuous draw rule). However, instead of a permanently installed device, you want to put an outlet in. This is where it's a problem, because there is no NEMA 40A outlet. NEMA outlets jump from 30A to 50A.

You cannot put in a 50A outlet because of the wire size -- to carry 50A, the wire must be at least 6 gauge, and I don't think that's what you have.

Thus, you have to step down to a 30A outlet, in this case a 14-30R. You can use the existing wires with this outlet, but you will need to replace the circuit breaker with a 30A breaker.

You'll then need the 14-30 adapter for the Tela UMC, and the car will then automatically charge at 24A (meeting the 80% continuous draw rule).

Another item that you have to check is the number of conductors in that receptacle box. The 14-30R receptacle requires 4 conductors -- 2 hots, a neutral, and a ground. If there are only 3 conductors in there (2 hot + ground), then you're stuck replacing the wire. The NEMA outlet for a 3-wire installation would be a 10-30R, but that's not allowed on new installations, and will not pass inspection.

If you want a higher charge rate, you can get a Tesla HPWC instead of trying to put in an outlet. Then you can use the existing wire (even if it's 3-conductor), and the existing 40A breaker. The Tesla HPWC can be set for a 40A breaker, and will then supply up to 32A to the car, very similar to the previous owner's EVSE.

Please note that all of this is based on the assumption that your existing wiring in that receptacle box is 8 gauge. If it's not, then none of this applies.

 

[FlatSix911]

If you have a 40A breaker, I'm going to assume you have 8 gauge wire. If you do not want to replace this wire, you're in kind of a pickle. You cannot put in a 50A outlet because of the wire size -- to carry 50A, the wire must be at least 6 gauge, and I don't think that's what you have.

Thus, you have to step down to a 30A outlet, in this case a 14-30R. You can use the existing wires with this outlet, but you will need to replace the circuit breaker with a 30A breaker. You'll then need the 14-30 adapter for the Tela UMC, and the car will then automatically charge at 24A (meeting the 80% continuous draw rule).

This is a good solution if you have 8 AWG ... go with the NEMA 14-30R.

 

[iluvmacs]

The issue is that the previous owner who used this circuit probably had a permanently installed EVSE rated for a 40A circuit (and therefore supplied 32A or less to the car to comply with the 80% continuous draw rule). However, instead of a permanently installed device, you want to put an outlet in. This is where it's a problem, because there is no NEMA 40A outlet. NEMA outlets jump from 30A to 50A.

You cannot put in a 50A outlet because of the wire size -- to carry 50A, the wire must be at least 6 gauge, and I don't think that's what you have.

Thus, you have to step down to a 30A outlet, in this case a 14-30R. You can use the existing wires with this outlet, but you will need to replace the circuit breaker with a 30A breaker.

This is inaccurate. The NEC allows you to jump up to the next receptacle rating available, so it is completely legit to put a NEMA 14-50 on a 40A circuit. You just have to be sure that whatever you put on meets the requirements of a 40A circuit -- in this case, not drawing more than 32A continuous. So, if using a v2 UMC, no problem, since it always limits to 32A. If using a v1 UMC, set the car to limit to 32A at this location. It is also suggested to label a 50A outlet that is on a 40A circuit so anyone else using it is aware of the situation.

Another item that you have to check is the number of conductors in that receptacle box. The 14-30R receptacle requires 4 conductors -- 2 hots, a neutral, and a ground. If there are only 3 conductors in there (2 hot + ground), then you're stuck replacing the wire. The NEMA outlet for a 3-wire installation would be a 10-30R, but that's not allowed on new installations, and will not pass inspection.

Also, correction to this, for reference/posterity: 3-wire is perfectly fine, but you would use 6-30 (or L6-30), not 10-30. 10-30 uses neutral instead of ground, and as you say can't be used now. 6-30 is totally acceptable, but Tesla does not make an adapter for it so you have to go custom. Since we know the circuit was an EVSE, it would have been wired for ground and not neutral.

 

[intjester]

First, I am not an electrician. You should consult with one.

However, the second gen UMC (Spring 2016 to present) that comes with the Model 3 conservatively assumes a 40 amp circuit from both 14-50 and 6-50 sockets, thus limiting the max draw to 32 amps / (80% of 40). You can read the charging table on page 5 in the UMC manual and see that this is so. The reason is that out in the world there exist 40 amp circuits which are wired to 14-50 sockets because NEMA does not have a 40 amp-specific socket in the lineup of socket options. https://www.tesla.com/sites/default...bile_connector_owners_manual_32_amp_en_US.pdf

This is an admirable decision on Tesla’s part, because it means any 40 amp circuits wired to 14-50 or 6-50 sockets will work safely because they will only be at 80% draw. If you replace the breaker and wiring to get from a 40 amp to a 50 amp circuit, you’re still only going to charge at 32 amps from that 14-50 socket on a UMC v2. That’s 64% draw. Extra safe, but not really necessary. Same deal with putting a Tesla Wall Charger on a 40 amp circuit. Way overkill for no practical benefit.

For $25, you can hang the end of the cable on a hook:
Model S/X/3 Cable Organizer

 

[spdn4cr]

Got it thanks all for all the info. This was all VERY helpful. This is a brand new house so there was no previous owner. From what I gathered from everyone this is what I have concluded:

I can install a NEMA 14-50 socket even though it is a 40A breaker and use it for the gen 2 UMC since it draws at 32A for my new Model 3. I just have to be careful to label the socket to show it is connected to a 40A breaker to prevent any future use by anyone expecting anything above a 32A connection and from what some have said doing it this way is not to code but would be stable since the gen 2 charger is only 32A now.

I hope I got that all right. Thanks again everyone.

 

[SZNJ]

Do you know what gage wire you have or the distance of the wire?

 

[spdn4cr]

I don’t know what gauge wire but the distance is decent since the outlet and the breakers are on opposite sides of a two car garage.

 

[xyeahtony]

First, it’s NEMA. . See my sig for Flasher’s FAQ that should answer all your questions.

But on the face of it, you need a 50 Amp breaker for a NEMA 14-50 outlet.

If you read what you said, it was 100% wrong. It needs a 50 Amp breaker and wires sized for that. 40 Amps is the continuous max load that is proper for that.

The UMC was reduced to 32 Amps to be safer since some were generating heat at 40, but that’s nothing to do with the circuit’s safety. If installed correctly, it should be able to run 40 Amps forever.

Technically speaking, installing a NEMA 14-50 on a 40amp circuit is perfectly within code. A lot of houses with electric ranges wire their NEMA 14-50s to 40 amp outlets. The reason being that there is no outlet rated for 40A, so the NEMA 14-50 is the closest match. If they put a NEMA 14-30 on a 40 amp outlet, the outlet would melt because the breaker would not trip between 30-40 amps. a 40amp breaker still protects the outlet at 40amps.

I suspect so many NEMA 14-50s are wired to 40amp outlets is why Tesla shipped the Gen2 UMC to max out at 32A vs the Gen1 UMC. Also in Canada, they can only draw 32amps max from their NEMA 14-50s continually due to what I suspect is the same reason.

 

[SomeJoe7777]

This is inaccurate. The NEC allows you to jump up to the next receptacle rating available, so it is completely legit to put a NEMA 14-50 on a 40A circuit. You just have to be sure that whatever you put on meets the requirements of a 40A circuit -- in this case, not drawing more than 32A continuous. So, if using a v2 UMC, no problem, since it always limits to 32A. If using a v1 UMC, set the car to limit to 32A at this location. It is also suggested to label a 50A outlet that is on a 40A circuit so anyone else using it is aware of the situation.

While allowed by code (40A circuit with a 50A receptacle), that is not a good installation for an EV outlet in my opinion. In most homes, the only place a 40A circuit + 50A receptacle is used is for the range/oven, which is a fixed-in-place appliance, and the outlet cannot be reached or utilized by the homeowner without removing the range/oven.

In a garage where EVSE devices will be plugged into the outlet, it is very easy to plug in an EVSE that would violate the 80% draw rule. If someone with a Model S visits his house and plugs in their Gen1 UMC into the 50A outlet, it will draw 40A, which will be 100% of the circuit rating in violation of the NEC.

The 40A circuit + 50A receptacle places the burden of NEC compliance on the user and the device selection. IMO, no installation should result in that situation.

Also, correction to this, for reference/posterity: 3-wire is perfectly fine, but you would use 6-30 (or L6-30), not 10-30. 10-30 uses neutral instead of ground, and as you say can't be used now. 6-30 is totally acceptable, but Tesla does not make an adapter for it so you have to go custom. Since we know the circuit was an EVSE, it would have been wired for ground and not neutral.

6-30R is not an option for the UMC since no Tesla adapter is made for that outlet. The only 3-wire outlet that could be installed that would work with the Tesla UMC would be the 10-30R. You would have to rewire the breaker box side of the conductors to 2 hot + neutral vice 2 hot + ground. But as has been covered, this is not a legal installation for new circuits anyway.

 

[JonathanD]

I have no electrical background but was hoping to do this on my own.

I don't want to say something like "it could burn down your house and kill you and everyone else in it" but I guess I just did.

Sorry for the hyperbole, but when it comes to stuff like this, I strongly suggest people get a professional to do it. A few hundred bucks is a cheap insurance policy.

 

[boaterva]

Technically speaking, installing a NEMA 14-50 on a 40amp circuit is perfectly within code. A lot of houses with electric ranges wire their NEMA 14-50s to 40 amp outlets. The reason being that there is no outlet rated for 40A, so the NEMA 14-50 is the closest match. If they put a NEMA 14-30 on a 40 amp outlet, the outlet would melt because the breaker would not trip between 30-40 amps. a 40amp breaker still protects the outlet at 40amps.

I suspect so many NEMA 14-50s are wired to 40amp outlets is why Tesla shipped the Gen2 UMC to max out at 32A vs the Gen1 UMC. Also in Canada, they can only draw 32amps max from their NEMA 14-50s continually due to what I suspect is the same reason.

This was my theory for the reduction also. I’ve had an offline detailed conversation with OP in more detail but the length of distance to the outlet may also have been a factor for the original owners.

 

[iluvmacs]

Got it thanks all for all the info. This was all VERY helpful. This is a brand new house so there was no previous owner. From what I gathered from everyone this is what I have concluded:

I can install a NEMA 14-50 socket even though it is a 40A breaker and use it for the gen 2 UMC since it draws at 32A for my new Model 3. I just have to be careful to label the socket to show it is connected to a 40A breaker to prevent any future use by anyone expecting anything above a 32A connection and from what some have said doing it this way is not to code but would be stable since the gen 2 charger is only 32A now.

I hope I got that all right. Thanks again everyone.

Just a reminder that if there's no neutral wire, you can't put in a 14-50. It will depend on how the original hardwired installation was done. EVSEs don't use a neutral, but sometimes the wire is there, capped off. If there's no neutral, either you have to add one, or you have to use a 6-50 receptacle instead (and Tesla does have a UMC adapter for that available).