Anyone know the charge rate for a standard 120V/30A RV outlet?

I test drove a Model S today and love it, but I have a question they could not answer. I plan to park my Tesla in the same garage where I store my RV. RV's use either 240V/50A or 120V/30A. My RV uses 120V/30A which I already have wired in my garage. The web site shows the charge time for a 240V/24A, but not my 120V/30A. Would the 120V/30A circuit provide a faster charge time than a wall outlet or do I need to call in an electrician?

Upgrade to a 240V/50A and use it for both your Tesla and RV. My guess is you will only get about 10 miles of range per hour of charge on the high side. You are only charging at 3.6KW (120V X 30A) vs 9.6kW (240V X 40A max amperage without HPWC) so you will get about 3 times more range per hour than what you currently have.

On any plug, you normally should charge at 80% of the breaker rating, so a 30a connection should be limited to 24a charging. And that is what Tesla plug adapters do, limit charge rate to 80% of breaker rating. However, Tesla does not provide a TT-30 adapter (which is what a 30A RV plug is), so you would have to make your own adapter. Also the Tesla UMC for some unknown reason restricts any charging at 120v to a maximum of 20 amps. So, with a home made adapter, you would end up with a charge rate of about 6 rated miles per hour of charging.

I would strongly recommend getting an electrician to install a Nema 14-50 240v plug instead.

120V 30A does not sound correct. Are you sure it's not 220V 30A? The formula though is straightforward.

Standard wall outlet 120V 15 amp. About 4 miles per hour
120V 30A = 8 (Double the amps, double the power)
240V 15A = 8 (Double the voltage, double the power)
240V 30A = 16 (Double both, and it's times 4)

The formula is approximately; Charging Time = Volts x Amps

When Volts = 120 and Amps = 15, charging time in hours = 4

"When Volts = 120 and Amps = 15, charging time in hours = 4"

I don't think so. That's about 60mi/hr.

jbunn, he is correct. It is 120V/30amp. It is aTT30 plug for smaller RVs like travel trailers and small motorhomes.

@jbunn - you can only draw 80% of the circuit's current on a continuous load. The formula you want is:

V * A * .86 / 308Wh/mi = rated miles per hour charge rate

Ie, 120V * 20A * .86 / 308Wh/mi = 6.7 rated mi/hr

(as shop points out, the UMC limits 120V charging to 20A)

Having to share an outlet seems pretty painful to me - the convenience of just keeping things plugged in would be worth the small cost of adding an outlet.

Short answer - call in an electrician.

@shop "Also the Tesla UMC for some unknown reason restricts any charging at 120v to a maximum of 20 amps. So, with a home made adapter, you would end up with a charge rate of about 6 rated miles per hour of charging."

If the OP used a NEMA 14-50 adapter, and then a NEMA TT-30P RV Plug to 14-50R Adapter like that found on (, would the UMC still limit the current to 20 amps, or could he dial it to 24 amps?

I agree with you that it is still better to add a 240V outlet.


Just a note, the Model S itself, not the UMC, restricts 120V charging to 20A. Perhaps if they release a TT-30 adapter they will also update the S's software to accept 24A from the TT-30 but for now we are stuck at a max of 20A at 120V regardless what you can provide the car.


@DouglasR, Yes, even in your scenario, you would be restricted to 20A. It kinda sucks, but then again, Tesla isn't supposed to support home made adapters. It would be really nice if Tesla came out with a TT-30 adapter, but considering they never made one for the Roadster (which still has a much large adapter selection), I would guess the importance of a TT-30 adapter is somewhere below that of the styling of the bolt heads holding the battery to the car.

Does anyone have real world experience charging at a 30A RV outlets? I am planning a trip next week, and they only have these available. What can I expect for a charging rate?

No real world experience, but I think the UMC would limit you to 16 amps. AFAIK there are only two 120v adapters for the UMC - one for 15 amp circuits (NEMA 5-15) that comes with the UMC, and one for 20amp circuits (NEMA 5-20) that is available for purchase. The UMC limits to 80% of circuit capacity, os you would be limited to 12 or 16 amps depending on which adapter you have. You would still need an adapter to connect the 5-15 or 5-20 plug on the UMC to the 30amp plug.

I actually bought a TT-30 to NEMA 14-50 adapter from an RV Parts store. The NEMA 14-50 adapter is on the end of your UMC plug, and would plug into the 14-50 to TT-30 adapter. I checked the wiring of this adapter, and they split the single 120 VAC line on the TT-30 plug end of the adapter to both hot wires on the 14-50 "recepticle" end of the adapter. While I have not actually needed to charge with this adapter, I assume that since the Tesla would see 120 VAC on both hot wires of the 14-50 UMC adapter, it would assume it was operating with a full 50-Amp circuit. The TT-30 adapter, however, is only rated for 30-Amps, so you would most likely need to dial down the current manually to 24-Amps (i.e. 12 amps per line, and most likely a setting of 12-Amps on the "Tesla Charging Panel"). This should give you around 6-mi/Hr of charging. Probably well worth a call to the Tesla Customer service guys to have them check with engineering and make sure.

tes-s, lammersc, please, you have both posted incorrect info - read on. And crazybrit, if you truly only have access to a 30A RV connection (hopefully only for overnight charging? You'll get about 5 or 6 hours of rated charge/hour), then I hope you realize you need to buy or build a special TT-30 adapter since Tesla does not make one?

The TT-30 to NEMA 14-50 adapters you find in RV and camping stores WILL NOT work for Tesla charging without modification. As you correctly pointed out, lammersc, they wire the single 120V hot from the TT-30 to both NEMA 14-50 hots. This results in the Tesla seeing 0V across the hots and thus won't charge.

To use a TT-30 adapter, you must rewire it so that it connects the 120V TT-30 hot to only one of the NEMA 14-50 hots, and then neutral to the other hot. It matters which hot gets the 120V (the UMC cares about that). This is documented in this document:

Or you can buy a ready made, properly rewired TT-30 adapter from here:

When using such an adapter, you start with the Tesla supplied NEMA 14-50 UMC adapter. So the Tesla thinks it can charge at 40A, and thus you must dial down your amperage to 24A. Tesla has a built in limitation, however, that it only allows charging at a maximum of 20A when you have a 120V connection.

And yes, I've used a TT-30 in the past. As I said, a slow but steady 5-6 miles per hour of charge...

I am making my own adapter from these instructions I understand the off-the-shelf adapters don't work. However I am looking for folks who have real world experience with the charging rate. There is a lot of speculation on this thread, and I have searched the forum and can't find anything.

Put in a 50 amp RV. You will be much happier.

Roamer, I think you are responding to the OP. I need to know the answer for a road trip

+1 @ Shop. I tried the adapter from an RV store and it did not work.

I have the adapter from evseadapters and it does work. If you only have the single charger it can only charge at half the 40A because you are only supplying power to one side of the charger.

@shop I sthe expert here and I defer to him. However, I have experience plugging in to several standard 120V wall outlet and to a 30ARV outlet at a marina. Charging rates in our experience for 120 range from 4-6 mph, none higher. A 240V 1450 is cheap and quick. Even an HPWC is fairly cheap given what we pay for these cars, and gives the advantage of always being at the ready (no coiling and uncoiling the UMC).

Thanks Shop. You answered my question. Our postings crossed in the ether.

Thanks for the info shop - you can buy a third party adapter to plug the 240v 14-50 Tesla plug into a 30amp 120v outlet.

I've bought the TT-30 adapter from and it works fine.

I did not experienced any limitation to 20 amps as sometime reported. Maybe it was the case with previous software versions (I am using 5.9). Set to 24 amps, I get a solid 14 km/h charge (8,75 miles/hour).

Hmmm. _thierrY, what version of 5.9 are you on? I'm on 5.9 (1.51.94) and I just tried it and I only got 20A, even though I had set my max amps to 24A. Maybe there are different car charger versions as well. Where are you located, what country?

thierr & shop.. If you don't have dual chargers the max you can get is 20A on 120V. Half the capacity of a single charger.

I have dual charger and I'm in Canada. I own my car since 3 weeks... so I guess I have the most recent software and hardware.

I've been using my RV TT-30 plug many time since and it always worked fine at 24 Amps. Yesterday, I plugged at 16h45 and it charged fine until this morning at 7h30. I got 200 rated-km charged.

OMG, maybe the difference is dual chargers versus single chargers. I honestly never thought that would be the case. I do only have a single charger.

Now why would a car charger only charge at 20A with 120V? Each charger has got to handle 40A since that's what I push through it with my single charger - 40A at 240V.

Can anyone else with dual chargers charge at 24A on 120V? This is the first time I've seen it confirmed anywhere on these forums.

The way I look at it is half as much in = half as much out of each charger.

Wow, this would be one of the oldest solved mysteries I've seen on this forum if this turns out to be the answer.

I've emailed ownership about this, we'll see if we get back anything interesting.

Here's my theory. There is a software limit per charger of 20A at 120V (simply due to an over protective programmer, ie. the limit isn't needed). In dual charger cars, the current gets split between the two chargers - which actually makes sense, it would be hard to do otherwise. So in dual charger cars, the software sees each charger getting 12A at 120V and all is fine.

Anyways, it seems that we've found yet another use case for dual chargers - it give you an extra 4A of charging at 120V. And if you are charging at 120V, every little bit extra helps!

I think MS limits charge current to 20A on TT-30, even though it supports 30A
It's still faster than 15-20A from some 120V TM adapters, but still, veeeery slow
You'd be lucky to get anything above 7mph