Installing a Nema 14-50 on a 30 Amp Breaker

[garth_angst]

That's the one I put in my panel for my HPWC. Is your panel Square D?

Oh, I have no idea. I thought Square D was just the manufacturer of the thing. I'll ask the electrician on Saturday. I'm sure he'll know what to get.

 

[destructure00]

Square D is the manufacturer of the breaker, but they also make panels. I'm pretty sure Square D breakers don't fit in competitor's panels and vice versa. Either way, there are other brand 60 amp breakers for about the same price that should work in whatever brand panel you have.

 

[eprosenx]

If that install is going in your garage, then the one you listed is fine, as long as you install bigger than 50 amps, which 60 amps is. If you decide to install a 50 amp or smaller then you need a special GFCI breaker.

You do *not* need a GFCI breaker if you are hard wiring into a Wall Connector (regardless of circuit size). NEC is not worried about folks getting shocked from the hard wired side of things. The Wall Connector has built in GFCI capabilities to handle the downstream protection.

You do need GFCI protection on all receptacles intended for EV's that are 50a and less per 2017 NEC Section 625.54.

 

[LCR1]

You do *not* need a GFCI breaker if you are hard wiring into a Wall Connector (regardless of circuit size). NEC is not worried about folks getting shocked from the hard wired side of things. The Wall Connector has built in GFCI capabilities to handle the downstream protection.

You do need GFCI protection on all receptacles intended for EV's that are 50a and less per 2017 NEC Section 625.54.

if he was going 50 or below I assumed it would be for a 14-50 and not a wall charger, no point in getting one unless you’re going 60-100

Edit: Also, the relevant code you’re looking for in that regard is 210.8

 

[eprosenx]

if he was going 50 or below I assumed it would be for a 14-50 and not a wall charger, no point in getting one unless you’re going 60-100

Edit: Also, the relevant code you’re looking for in that regard is 210.8

Yeah makes sense. Though the more I think about the math, if you want to always keep your UMC in the car, a second UMC is $300, then you save about $100 not doing the GFCI breaker (and just doing a regular $10 240v regular old breaker instead), and let's assume you want the $33 Tesla cable end holder, plus say $70 for the nice Hubbell NEMA 14-50r receptacle, and maybe a 3D printed holder to hold the UMC on the wall, then in that case the Wall Connector is actually cheaper by a few bucks. ;-) It also will do 40a on a 50a circuit (compared to the UMC Gen 2 which will only do 32a), and if you want you can put it on up to a 100a circuit and do 80a (though no current model Tesla's can use that much!).

Btw, 210.8 is where most of the GFCI requirements are tucked, but for "Dwelling Units" (aka homes) the 2017 NEC only requires GFCI's for 120v 15a or 20a circuits in 210.8.

625.54 is where they added the GFCI requirement for circuits up to 50 amps (note that our 240v circuits in residences are 120v to ground since it is split phase, so this DOES apply).

 

[RaeW]

Except you never said that you said the car knows what size circuit it's plugged into, when in fact it doesn't.

My 2015 MS knows what plug (socket) it is connected to!

 

[Firemansim]

I have a 240-volt dryer circuit on a 30 amp breaker that I'm not using (I have a gas dryer) I was thinking putting in a Nema 15-40 on this 30 amp breaker to charge a model 3 long range. Here are my questions:

1) Will this work?

2) About how many miles of charge can I get off of this setup with a 30 amp breaker?

Thanks for the help.

I wouldn't change the outlet for reasons others have already covered, but you can create your own pigtail to go from 14-30P to 14-50R, and then manually drop your charge amperage to 24 (max for a 30A circuit). I did this because I had the spare parts and the skill. If you had to buy all from like a Home Depot you'd be close to $35, so it's better to just buy the Tesla adaptor.

 

[LCR1]

My 2015 MS knows what plug (socket) it is connected to!

But it doesn't know what circuit it's hooked up to, which is why that guy kept saying. a 14-50 socket/plug doesn't mean it's hooked to a 50 amp breaker or 50amp rated wiring.

 

[eprosenx]

I wouldn't change the outlet for reasons others have already covered, but you can create your own pigtail to go from 14-30P to 14-50R, and then manually drop your charge amperage to 24 (max for a 30A circuit). I did this because I had the spare parts and the skill. If you had to buy all from like a Home Depot you'd be close to $35, so it's better to just buy the Tesla adaptor.View attachment 393619 View attachment 393619 View attachment 393620 View attachment 393621

Also, not recommending this, but a fun thing to know:

You can just cut the neutral pin off a Tesla 14-50 adapter (it is totally unused) and plug it in. 14-30 and 14-50 are the same other than the neutral pin.

 

[TexasEV]

My 2015 MS knows what plug (socket) it is connected to!

No it doesn’t. It only knows what adapter is attached to the UMC. If you then use an adapter to plug it into a different wall outlet, the car still thinks it’s plugged into the outlet intended for the UMC adapter, not the one it’s really plugged into.

UMC has adapter A. You use an A to B adapter to plug the UMC into outlet B. The car thinks it’s plugged into outlet A, not outlet B.

 

[RaeW]

But it doesn't know what circuit it's hooked up to, which is why that guy kept saying. a 14-50 socket/plug doesn't mean it's hooked to a 50 amp breaker or 50amp rated wiring.

t

No it doesn’t. It only knows what adapter is attached to the UMC. If you then use an adapter to plug it into a different wall outlet, the car still thinks it’s plugged into the outlet intended for the UMC adapter, not the one it’s really plugged into.

UMC has adapter A. You use an A to B adapter to plug the UMC into outlet B. The car thinks it’s plugged into outlet A, not outlet B.

 

[RaeW]

So it knows the 14-50 adapter is 40 W. When I change it to a 14-30 won't it know that it's 30 W?

 

[juliusa]

I have a 240-volt dryer circuit on a 30 amp breaker that I'm not using (I have a gas dryer) I was thinking putting in a Nema 15-40 on this 30 amp breaker to charge a model 3 long range. Here are my questions:

1) Will this work?

2) About how many miles of charge can I get off of this setup with a 30 amp breaker?

Thanks for the help.

Yes, it will work
Yes, it meets code.
No, you should not do it. Install a 14-30 outlet and get the adapter from Tesla.

 

[eprosenx]

Yes, it will work
Yes, it meets code.
No, you should not do it. Install a 14-30 outlet and get the adapter from Tesla.

You know, I just realized we never qualified what conductors are available in the wall right now. Is the current receptacle a 10-30 or a 14-30? If a 10-30 it is possible there is only hot-hot-neutral, no ground. If there is not a ground available in addition to the neutral then you can't convert it to a 14-30. Regardless though, you can get a 10-30 adapter for the Tesla (less preferred than a 14-30, but will work fine, meet code, and be safe).

To the comment above about this "meeting code" I think that is untrue. The issue is that when using a Model 3 with a UMC Gen 2 your intended load is 32a continuous (so you have to plan the circuit as if it is 40a). That circuit is only 30a. Setting it to a lower charge rate in the car via software is generally not considered sufficient for load calculation reasons. So the only code compliant solution here would be to get a 14-30 or 10-30 adapter from Tesla for the UMC Gen 2.

 

[juliusa]

To the comment above about this "meeting code" I think that is untrue.

Section 210.21(B)(1). If a single receptacle is installed on a branch circuit, it shall have an ampere rating of not less than that of the branch circuit.

 

[eprosenx]

Section 210.21(B)(1). If a single receptacle is installed on a branch circuit, it shall have an ampere rating of not less than that of the branch circuit.

Yes! Indeed, that part is to code (and I frequently am the one pointing that out!)

But- There is also:

210.19 Conductors - Minimum Ampacity and Size.
(A) (1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Conductors shall be sized to carry not less than the larger of 210.19(A)(1)(a) or (b).

So "the load to be served" is 32a continuous when you are using the NEMA 14-50 adapter on the UMC Gen 2. So you have to calculate it as 40a. So the 30a wire and breaker is not sufficient.

If you use a 14-30 adapter on the UMC then it is a 24a continuous load and that fits.

 

[juliusa]

The "load to be served" is 24a, not 32a.

 

[juliusa]

Suppose a 2013 MS owner with a gen1 UMC wants to get the maximum charge rate at their home. An electrician does a load calculation and determines the panel can handle a 40amp breaker and 32a continuous load. The outlet is located 5 feet from the panel. What breaker, wire gauge, and receptacle would meet code and the owner's objectives?

 

[M3BlueGeorgia]

So it knows the 14-50 adapter is 40 W. When I change it to a 14-30 won't it know that it's 30 W?

Absolutely, it'll know it is a 30A rated socket and therefore won't try to draw more than 24A continuous (80% of rated).
Which is about 22mph.

BTW: That's what I use, because when I rewired the house a year before the Model 3 was announced, I only ran 8 gauge wire to the carport. So I use 14-30 for safety.

 

[eprosenx]

The "load to be served" is 24a, not 32a.

The original poster was asking about putting a NEMA 14-50 receptacle on a 30a circuit (even though they transposed the digits and wrote 15-40). So when you plug a UMC Gen 2 into a NEMA 14-50 using the included Tesla adapter it will try to draw up to 32 amps. So "the load to be served" is 32a. If you instead put a 14-30 adapter on the UMC Gen 2 and plugged it into a 14-30 receptacle then "the load to be served" would be 24a.

Suppose a 2013 MS owner with a gen1 UMC wants to get the maximum charge rate at their home. An electrician does a load calculation and determines the panel can handle a 40amp breaker and 32a continuous load. The outlet is located 5 feet from the panel. What breaker, wire gauge, and receptacle would meet code and the owner's objectives?

None. If you connect a UMC Gen 1 using the NEMA 14-50 adapter then "the load to be served" is 40a continuous (requires a 50a circuit). You can't per NEC plug that into a 40a circuit. And if the load calcs won't let you serve a 40a continuous load (50a circuit) from that electrical service / panel / feeder you are stuck.

What you could do is buy the NEMA 14-30 adapter for the UMC Gen 1 and install the corresponding receptacle / wire / circuit and charge at 24a continuous. This is one reason Wall Connectors are nice as they have more granular max amperage choices.

Absolutely, it'll know it is a 30A rated socket and therefore won't try to draw more than 24A continuous (80% of rated).
Which is about 22mph.

BTW: That's what I use, because when I rewired the house a year before the Model 3 was announced, I only ran 8 gauge wire to the carport. So I use 14-30 for safety.

FYI, 8 gauge Romex (NM-B) copper wire is good for 40 amps. You could install a NEMA 14-50 receptacle on that wire on a 40a breaker and use a UMC Gen 2 and charge at 32a. This is perfectly acceptable under the 2017 NEC as long as your load calculations allowed for it.

Using a 14-30 on a 30a circuit is perfectly fine too (and more conservative), but the NEC itself is generally conservative so I would not have any issues doing the 40a circuit as I describe.