EV Charging on a TT-30 30-Amp RV Plug

50-Amp vs. 30-Amp RV Receptacles
Image source: Karl Bloss
Note: This is Tesla-heavy content related to the Universal Mobile Charger (UMC).  However, the discussion of adapters is relevant to other EVs.  

In my recent winter road trip, I visited a friend who informed he had "some kind of RV plug" behind his house from a previous RV owner.

If you prefer a video overview with less detail, jump to this short YouTube video on the topic:  https://youtu.be/m0gfpz_h100

RV Plugs Explained

When we hear about RV power plugs, it's usually just in reference to a "30-amp" and a "50-amp" plug.  Unfortunately, amps don't tell the whole story because what we are really after is power (Watts) rather than flow of electricity (amps).  If the technical details are too much for you, skip down to the Bottom Line adapters section.

Roughly speaking:

Watts (power) = Volts (potential) x Amps (flow)

Watts or Kilowatts (KW) are what give an indication of how quickly we can charge for more range.

What's missing in the RV plug description is that the 50-amp NEMA 14-50 receptacle delivers at 240 volts and the 30-amp TT-30 receptacle delivers 120 volts.  Using the above power calculation, the NEMA 14-50 delivers 3.3 times the power and thus EV charging speed of the TT-30.

Back to my road trip, my friend confirmed he has a 30-amp RV receptacle, not the more prevalent 50-amp.  While I would prefer the NEMA 14-50, compared to a standard 120V household outlet that is typically wired for 15 amps, the TT-30 will deliver twice the power of a standard outletThat's worth getting an adapter.

A generic TT-30 to household 120V adapter
Image source: Karl Bloss

What Kind of Adapter?

The TT-30 outlet lets small Travel Trailers (thus "TT") get 120V power in campgrounds with higher power to run such devices as air conditioners and refrigerators.  For those RVs not equipped with a TT-30 plug, there are adapters available.

TT-30 to NEMA 5-15 Adapters

At first glance, it would seem the way to handle this situation is drop by your local home improvement store and pick up an adapter to a standard 120V outlet (aka NEMA 5-15) like this one from Home Depot.  That would work, but your 120V-capable EVSE (aka charge cable) will only draw 12 amps (80% continuous draw of 15 amps).  So that's no better than using a regular 120V outlet.

Non-EV 50-amp Adapters

While at home Depot, you can also find RV adapters (like this one) that let you adapt a TT-30 male to a NEMA 14-50 female female plug in case your EVSE has a 50 amp plug.  These will not work for EV charging because they are designed for a different purpose, namely RV power.  If you plug one of these adapters into your EVSE, you will likely get a fault and it won't charge your car.

TT-30 to NEMA 14-50 EV Adapter
Image source: EVSEAdapters.com

Bottom Line:  Get an EV-specific Adapter

Generic Adapter

If you want to use your EVSE with an NEMA 14-50 plug on a TT-30 receptacle, equip yourself with something like this adapter from EVSEAdapters.com:  https://www.evseadapters.com/products/tt-30p-to-nema-14-50r-ev-adapter/

Note that you may need to dial down the amps on your EVSE so as not to overload the circuit and trip the circuit breaker or worse, the wiring.  The proper setting for continuous current draw is 80% of the maximum circuit rating so 0.8 x 30 = 24 amps.

TT-30 to Tesla UMC Adapter
Image source: EVSEAdapters.com

Tesla UMC Adapter

Since I have a Tesla Generation 1 Universal Mobile Connector, I chose to get the associated adapter from EVSE Adapters:  https://www.evseadapters.com/products/tt-30-adapter-for-tesla-model-s-and-x-gen-1/  EVSEAdapters.com also carries a similar adapter for the Generation 2 UMC that typically comes with the Telsa Model 3.

The advantage of the UMC adapters is this adapter has an internal circuit that communicates with the car to automatically set the appropriate 24 amp charging current. No need to manually set the current – simply plug it in.  As shown in the YouTube video, I just plugged it in and the car automatically switched the charging amps to 24.

End Result

I plugged in and got about 3 KW of power, which is twice of a household circuit.  That translates into about 6-8 miles of range per hour of charging compared to about 3-4 miles of range per hour on my Model S.  In my video example, this took me from 52% state of charge at arrival in the late afternoon to 90% at around 5 AM the next morning plus I had juice to warm up the cabin in the morning without impacting the battery charge.  Had I stuck with a 120V circuit and the associated 1.6 KW, my departing state of charge would have been closer to 70%.

Zero DSR charging with Tesla UMC and Tesla Tap
Image source: Karl Bloss

Added Bonus: Usage with my Zero DSR

I carry a spare Tesla UMC when I travel with my Zero DSR which is outfitted with a Tesla Tap adapter.  This adapter lets me plug my UMC or any Tesla Destination Charger (although NOT Superchargers) into my Zero's J-1772 Charge Tank.

With the combination of the TT-30 adapter and the above setup, I can also charge my Zero or even Nissan LEAF at a campground with a TT-30 receptacle.  3 KW translates to about a 4-hour charge time on the Zero or a 10-hour charge time on my LEAF.  Again, still much better than a standard outlet.


If you are in the market for a Tesla Model S, Model X, or Model 3, Tesla has reestablished its referral program.  Feel free to use my referral code to get 5,000 miles of free Supercharging (at the time of this publishing) for your Tesla:  http://ts.la/karl5062


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