I have used an EV charger for my car that is "slow" level 1 charging. It's rated for up to 20amps using a NEMA 6-20 plug, however it came with an standard 5-15 adapter (2ft long) that I've been using successfully nightly for 2 years.

I just moved to a new home, and I installed a 50amp circuit breaker, ran (23ft) 6awg wire with conduit from panel in basement to garage, where I then wired and installed a Hubble NEMA 6-50 outlet.

I will eventually buy a 40amp charger, but for now I'm stuck with a NEMA 6-20 charger and a 6-50 outlet.

I see on amazon lots of "adapters" and extensions for 6-20 to 6-50. Are these safe? Is it that simple? Can I leave it plugged in and charge my car in nightly without my house burning down?

I'm assuming my 5-15 adapter provided by manufacturer is safe and have had no problems using it for past 2 years - but can I do the reverse safely?


2 Answers 2


Much safer to have the breaker close to what you need.

Most places now require GFCI protection for garages/outside plug in devices. Most larger EV chargers can be hardwired to bypass this requirement(they have better gfci protection).

Can keep the 6 gauge wire, but replace with a 20 amp breaker for now. Can pigtail 12 or 10 gauge wire to the 6 gauge if the 20 amp breaker does not take 6 gauge in the panel.

50 amp breaker will allow much more power to go though if there is a problem than a 20 amp breaker.

  • 1
    I checked a 20 amp breaker I have in my part box and the largest wire it will accept is 8AWG, so pigtails. Of course changing the breaker should call for changing the outlet, I realize that's implied but I comment to remove any doubt. Perhaps a 30 amp breaker and outlet will take 6AWG wire, that adds safety factor without the added risks of pigtails. A 40 amp breaker is permitted on 50 amp outlets, but that's not a big improvement on safety. The 50 amp breaker would need to be put back once 40 amp charger arrives due to 80% load requirement. Thoughts I'd add to a very good answer.
    – MacGuffin
    Commented Oct 8, 2022 at 22:13
  • I understand everything you are saying, but kinda defeats my purpose of installing the outlet and breaker for a 40amp future device... might as well just swap the breaker and outlet directly for a nema 6-20 and not use an extention - and if i'm doign that, i might as well just keep using the 5-15 adaptor in a regular wall socket...
    – BHJO
    Commented Oct 10, 2022 at 16:21
  • @BHJO A 15 amp 120v circuit has a max of 1800w. A 20 amp 240v circuit has 4800w, which should give faster charging. You can keep the wires in place, and when you get the 40 amp charger, it is only a few minutes to switch the breaker/outlet. Larger wires are allowed on circuits, code just says the smallest allowed, not the biggest.
    – crip659
    Commented Oct 10, 2022 at 16:46
  • @crip659 - this makes sense now - but per a comment above, my 6awg wire is too big for a 20amp breaker - if i get a 30amp breaker is that safe? or still like... pushing it with a 20amp outlet?
    – BHJO
    Commented Oct 10, 2022 at 19:02

NEMA 5-15 through 6-20 plugs

Due to continuous-load rules, EVs charge at 80% of the stated watt rate.

All my advice here assumed you had a full electric. Plug-in hybrids need less.

Let's get de-confused about plug types!

You can't get 120V from a NEMA 6-20 safely or legally (it bootlegs ground)... so if you have been using an adapter, it's cheap junk and not UL listed. See notes below. The common 120V plug will only charge at 1.4 kW, which is not enough.

If you had obtained the factory-provided and correct plug dongle for NEMA 6-20, then your charging would have happened at a strong LEVEL 2 charge rate of 3.8 kW, which is plenty fast for 99% of people 99% of the time.

You must use the factory plug dongles. No unlisted adapters!

And here's why. Those plug dongles have microchips embedded in the plug. They are there because of a UL requirement to sense temperature, and throttle back or shut down if the plug gets hot. However the microchip has a second job: to tell the car the available amps. (which are 80% of the socket rating).

enter image description here

That thing in purple is a microchip. It uses the 4th pin in the socket adapter to communicate with the EVSE and EV. (the 4th pin is not neutral). It is literally saying "You are authorized to 12A" - or if the plug gets hot, "you are authorized to 6A" etc. This happens through the magic of 1990s era microcontroller tech.

As you see from the above diagram, one cannot cut the plug off and change it, because the microchip is in the plug.

But using an "adapter" or cheater extension cord is even worse. Because now, the microchip is wrong about the allowable amps on the circuit.

This is a problem if the EVSE dongle plug is larger than the ultimate outlet. Imagine you had used the NEMA 14-50 dongle plug to connect into that 20A circuit! Because then, the car would hear it was good for 32A on the 20A circuit.

In your case, your NEMA 5-15 dongle was telling the car it could draw 12A. If your cheater was dangerously wired to give 120V, you would have been doing level 1 charging at 1.4kW, and your car would be regaining only 30 to 40 miles per night, and you'd notice that, I would think, yes?

Whereas if the cheater adapter was dangerously wired to deliver 240V to the 120V plug (!!!!) Now an EV, unlike most other loads, will accept 240V just fine. So it was hearing "only draw 12 amps" and doing that at 240V, so you were in fact doing (booming voice) level 2 charging albeit at the low end, for 60-80 miles a night.

I wish I could go back in time 2 years and tell you to buy a NEMA 6-20 dongle for your travel EVSE. That would have been safe, and delivered full power level 2 charging for 100-120 miles in a 10 hour charge (more for a full evening of course).

You don't need to buy brand new EVSEs, you can hit up Craigslist or Facebook Marketplace for a used one. Take your car to meet the person and test it at their house.

Proper 240/20A is plenty

First, 240V/20A is probably adequate for your EV charging needs unless you have a commute in excess of 100 miles daily. See 34:43 in this video.

In fact there may be important reasons not to push your house's electrical system so hard. You need to do a New Load Calculation on the house's service anytime you add a large load like an EVSE. Typically builders don't waste money putting in vastly larger services than required, so a 50A EV circuit usually does not fit, and would necessitate a service upgrade or load shed devices. However a 20A is much more likely to fit.

So you may want to consider sticking with 20A, although you may want to consider a wall unit - using the travel EVSE for daily charging gets real old real fast.

A wall mount EVSE is preferably hardwired. This avoids the costly, stupid and redundant GFCI requirement a few states place on 240V sockets. EVSEs already contain a smarter and more capable GFCI.

Do not buy electrical gear - especially plug adapters! - mail order.

Be extremely wary of buying electrical gear on "eBay-like" sites such as Amazon. If you didn't know Amazon is eBay-like, yeah, surprise - that's the Amazon Marketplace, which is dominated by cheap, dangerous shovelcrud straight off Alibaba, and those results are blended with real Amazon results.

Mail order is only safe when dealing with specialty stores like Home Depot (who are simply selling their store stock on the website) or McMaster-Carr or GALCO who sell to industry who won't accept unlisted things. Grainger is mostly OK, Fastenal is pretty slimy on their electrical gear. However beware websites like Sears or Walmart which blend in Amazon or EBay results.

Reliable equipment is indicated by a UL Listing mark featuring the familiar UL-in-circle logo typically with C or C/US and a 6-8 digit file number. The CSA circular mark, or the ETL mark is acceptable. These are approved competitors to UL.

UL is very aggressive about enforcing its mark in China, so UL marks on the device are usually correct. However UL can't do anything about claims in the product listing or "certified to UL specifications" claims which is not the same as a UL Listing.

UL-listed 50A to 20A adapters exist. UL will approve them if they include internal 20A fuses or circuit breakers. The fuses may not be replaceable, but that shouldn't be a problem for an EVSE with a 20A plug dongle, which is telling the car to draw no more than 16A.

  • few thoughts, 1. I have 200amp service and a 22kw standby generator - I've called about loadshedding devices for local electrians but no call backs for some reason?? 2. how do I do a load calculation? 3. I'm planning on buying another EV that is more than just a hybrid first 20mi are electric like the car i have now so i wanted to upgrade. 4. I used a bryant UL 50amp outlet, and a 50amp circut breaker (eaton to match my panel), and the wire i used was branded as ROMEX. Do you have a specific brand or type of adaptor suggestion i can buy? for the 50 to 20 downgrade?
    – BHJO
    Commented Oct 10, 2022 at 16:16
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    @BHJO let me get back to you on those. You only need load sheds for the generator if it's on an automatic transfer switch. If you use a $70 manual interlock, no need. I was assuming you had a full-on straight electric, and 20A/240V is still adequate for 99% of those. Commented Oct 10, 2022 at 20:39
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    @BHJO -- have you considered having your generator transfer switch be set up feeding a subpanel, instead of having as a "whole-house" generator set? Commented Oct 11, 2022 at 0:13
  • @threephaseeel - YES! this is exactly what i want, a subpanel that my 22kw backup generator provides specific (heat, ac, fridge, sump pump, washer/dryer, microwave, and home office etc.) and if the lights/other outlets and car charger go out - no big deal - but for some reason No electrian near me is calling me back or they are all just so busy with bigger jobs???
    – BHJO
    Commented Oct 14, 2022 at 13:43
  • 1
    @BHJO -- yeah, start reading up, and ask another question with details about your situation if you want help with the generator thing Commented Oct 15, 2022 at 0:14

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