14-50 vs 14-30 Question

[Kirby64]

Code clarification: The breaker has to be sized for the LOWEST rating of any wire or device in the circuit (exception: 15 amp outlets on a 20 amp circuit, since you can't plug in a 20 amp appliance to a 15 amp outlet). So this means that yes, you can put a 14-50 outlet on a circuit that is protected by a 30 amp breaker. Just like you can run 6 gauge wire to a 20 amp outlet it's OK by code, but you have to have no more than a 20 amp breaker protecting the circuit. Also, code says that if you are going to draw continuously for 3 hours or more you have to de-rate by 20%. So even if everything in the circuit is rated for 30 amps, you can't draw more than 24 amps, by code, for more than 3 hours. So set your car to charge at 24 amps at that location. If you want 30 amps and the car will be charged at that rate in less than 3 hours, it's OK to bump the charge rate up to 30 amps. There's nothing stopping you from drawing 30 amps for 10 hours straight since code doesn't make you put in a 24 amp breaker, but you'd still be violating code.

Per code, you are not allowed to put a 30 amp breaker wired up to a NEMA 14-50. Code mandates that the breaker match the outlet, period. The only exceptions to that are the 50 amp outlets (14-50, 6-50, etc), which allows a 40 amp, but NOT a 30A breaker, and also the 15/20A 120V outlets, since those are intended for multi-drop branch circuits. While I agree it will be safe (assuming you don't repeatedly trip the breaker, and only uses 24A max), it isn't up to code and would fail an inspection, regardless of the wire backing it.

 

[Jeffcm3]

I see the OP purchased the adapter. Sounds good.

For these kind of ideas one should call an electrician.

We also know nothing about the age of the house, wiring, etc. which would contribute to the decision on upgrading a circuit.

Btw, if the outlet was replaced with a 14-50, then when the house is sold etc and an inspection is done this will be an issue.

Fwiw I have a 14-30 dryer outlet and simply got the Tesla 14-30 adapter. And the car occasionally trips the breaker, so I turn it down a bit in the car charger UI.

 

[bandwagon]

Already ordered the 14-30. Thanks guys.

That's the 'right' answer. You could get an adapter and manually limit the amperage (24amp, not 28 though) - maybe ok in a pinch, but not worth the risks.

You might check with your local service center to see if they have the adapter in stock - I ordered mine as well, but would be nice if you don't have to wait.

 

[Rocky_H]

Per code, you are not allowed to put a 30 amp breaker wired up to a NEMA 14-50. Code mandates that the breaker match the outlet, period. The only exceptions to that are the 50 amp outlets (14-50, 6-50, etc), which allows a 40 amp, but NOT a 30A breaker, and also the 15/20A 120V outlets, since those are intended for multi-drop branch circuits. While I agree it will be safe (assuming you don't repeatedly trip the breaker, and only uses 24A max), it isn't up to code and would fail an inspection, regardless of the wire backing it.

Not actually true, but that is good practice.

 

[Gray468]

Here are some other data point.
I use my dryer outlet, converted dryer to gas. Before that I was constantly plugging/unplugging. But I had an electrician replace the outlet with an “industrial” version that would be more tolerant of repeated plug/unplug. Was that a waste of time/money?

According to the car (2017 Model S 100D) with upgraded charger) Dryer delivers 24 amps, 235 volts for 17 m/hr.

A local free charger (heavily in use by all sorts of EVs) delivers 233 volts at 69 Amps for 50 mph. It does have a thick wire and I wonder if it can actually deliver more amps than I can consume (I believe my onboard charger is rated for 72 amps).

Closest SC is 35 miles. So whenever I see this 50 mph beauty available, I soak up what I can while I go shopping. Damn convenient.

 

[Kirby64]

Not actually true, but that is good practice.

Huh, well call me corrected. I had to re-read the NEC multiple times, but 210.21(B)(1) explicitly says as long as the outlet is oversized for the branch circuit then it's allowed. That being said, there's multiple bits in there about how the load cannot accidentally pull more than is allowed... so a UMC, even if dialed back, has the potential to pull 32A if the GPS-based current limiting gets reset or something. I think it gets into iffy territory there...

Regardless, 14-30 is the correct answer here. Especially given this is in a dryer area, so if the place ever changes hands... you don't really want to have a 14-50 that is backed by a 30A breaker since folks aren't likely to actually check that thing.

 

[Occhis]

Can you check the wire gauge of your 14-30 outlet? if is 8 AWG you can change the Breaker/Outlet and use the same wire, but if is 10 AWG, then you should buy the 14-30 adapter.

I thought #6 wire is to be used with 50 amp breaker. That’s what the electrician who installed my 14-50 outlet and breaker used.

 

[Rocky_H]

Huh, well call me corrected. I had to re-read the NEC multiple times, but 210.21(B)(1) explicitly says as long as the outlet is oversized for the branch circuit then it's allowed. That being said, there's multiple bits in there about how the load cannot accidentally pull more than is allowed... so a UMC, even if dialed back, has the potential to pull 32A if the GPS-based current limiting gets reset or something. I think it gets into iffy territory there...

Regardless, 14-30 is the correct answer here. Especially given this is in a dryer area, so if the place ever changes hands... you don't really want to have a 14-50 that is backed by a 30A breaker since folks aren't likely to actually check that thing.

It is kind of a strange thing in the code. There is a section that is about if you have multiple outlets on the branch, and then it has a table showing exactly what types of outlets have to match the circuit rating, but if it's one dedicated outlet, then it can have a very undersized circuit breaker. You're right that the UMC wouldn't be a good example, because it really is supposed to have at least a 40A circuit, and turning it down in the car doesn't count to make it lower, but there are other brands of EVSE that are for 20A or 30A circuits, but still have a 6-50 or 14-50 plug, and that's where this weird case would apply.

I thought #6 wire is to be used with 50 amp breaker. That’s what the electrician who installed my 14-50 outlet and breaker used.

That is dependent on what type of wire. Check this ampacity table:
Ampacity Charts - Cerrowire
See the first column where it's 60 degrees C for NM-B? That is Romex cable. So where does it meet the requirement for a 50A circuit? It's 6 gauge.
But if you look at the second or third columns, those types like THWN or THHN are individual wires run through conduit. So look what size covers a 50A circuit. It's 8 gauge.

So someone could do 8 gauge in conduit, but it's always OK to upsize the wire a little, though, so for the K.I.S.S. principle, it's safe to always recommend 6 gauge for 50A circuits all the time, no matter what kind of wire is being used.

 

[G78M3]

Already ordered the 14-30. Thanks guys.

By the way, you will be more than OK with the 14-30. That’s what I have and I have never ever needed more speed, not even for road trips. Some even argue that every day charging at 24A is healthier for the battery than 32A.

A big plus: now you have an adapter that will come in handy when road tripping and visiting friends, most houses have a drier in the garage where you can charge, but certainly not everyone has a 14-50 outlet.

 

[Watts_Up]

By the way, you will be more than OK with the 14-30.
That’s what I have and I have never ever needed more speed, not even for road trips.
Some even argue that every day charging at 24A is healthier for the battery than 32A.

A big plus: now you have an adapter that will come in handy when road tripping and visiting friends,
most houses have a drier in the garage where you can charge, but certainly not everyone has a 14-50 outlet.

You should also request to your local electrical power company to switch to a Time of Use (ToU) plan,
so you might get something like 50% discount at night for 8 hours in general.

So 8 hours at 22 miles / hour will give you 176 miles. Most users have a 50 miles commute, so should be sufficient.

I would also recommend installing a Watt meter to have a good idea of your consumption See below "energy".
This type of device can fit inside a regular socket outlet box.

 

[TexasEV]

Some even argue that every day charging at 24A is healthier for the battery than 32A.

That’s a ridiculous argument by people who have no clue. It’s 5.7 kW vs. 7.6 kW, in a battery that routinely charges at an order of magnitude higher power at superchargers. Even using home AC charging by Wall Connector, 72A was standard for years with no suggestion that it would have any ill effect on the battery.

 

[Rocky_H]

You should also request to your local electrical power company to switch to a Time of Use (ToU) plan,
so you might get something like 50% discount at night for 8 hours in general.

No, people should not just request to switch to time of use without checking their numbers to see if it makes sense for them. I've seen plenty of people on this forum who have run the numbers for their situations, and it turned out to be much more expensive on time of use. If you don't drive a lot of miles, the overnight use for the car might not be very much compared to the overall use of the house, and time of use plans are creating a tradeoff of cheap overnight rates for ridiculous, extortionate, sky-high rates during the daytime. So it may cost you more if you have a lot of daytime use that you can't shift away to other times.

 

[Rojer Lockless]

I pay 9.5c kwh 24/7 in Texas, I'll be fine.

 

[davewill]

No, people should not just request to switch to time of use without checking their numbers to see if it makes sense for them. I've seen plenty of people on this forum who have run the numbers for their situations, and it turned out to be much more expensive on time of use. If you don't drive a lot of miles, the overnight use for the car might not be very much compared to the overall use of the house, and time of use plans are creating a tradeoff of cheap overnight rates for ridiculous, extortionate, sky-high rates during the daytime. So it may cost you more if you have a lot of daytime use that you can't shift away to other times.

I can second that, although solar usually helps with that quite a bit. I was happy that my utility added a feature to their website that runs the numbers for all of their rate plans of your last 12 months of usage to see what you would have paid. It turned out that their regular EV-TOU and non-TOU were very close for me after they shifted the peak times into the evening, negating much of my solar advantage over non-TOU. However, they had a new EV-TOU that included a $16 monthly fee that buys down the rates some which cut things in half for me.

 

[cbaaz]

FYI - our power provider (SRP) will switch you to TOU and if it does not result in savings compared to standard plan over 90 days, they will refund the difference and switch you back. Those TOU daytime rates are *much* higher, for sure. At first glance, I don’t think TOU would save me anything.

Maybe other POCOs offer a similar trial <?>