50 amp circuit for future-proofing

Discussion in 'Prime Plug-in Charging' started by Billy sharpstick, Nov 25, 2019.

  1. Billy sharpstick

    Billy sharpstick New Member

    Jul 12, 2019
    Micanopy FL USA
    2019 Prius Prime
    Prime Premium
    I am planning to install a 240V circuit for a level 2 charger. I only need a 20a circuit for my Prime, but want to put in a 50a circuit for future value when we sell the house(in a couple years or so).
    I can put in a 20a breaker, #6 wire and a 20a GFCI outlet for now, and make it fairly easy to upgrade the breaker and outlet later.
    Or I can put in a(expensive) 50a GFCI breaker and 50a range outlet now. This would require an adapter to go from the 50a to 20a. Logically, for safety, this would leave the 20a wiring unprotected except by the 50a breaker.
    Can level 2 chargers plug in to 50 or 30 amp circuits safely? Worse case, the 12(?) ga wire just downstream of the plug shorts out and causes a fire because it has a 50a breaker feeding it!
    What is the best, accepted and safe way to do this? (I know how to make it work, and/or safe and/or legal. I am a retired electrician and haven't forgotten all of that stuff yet.)
  2. fuzzy1

    fuzzy1 Senior Member

    Feb 26, 2009
    Western Washington
    2012 Prius
    Not being an electrician myself, merely an electrical engineer (which doesn't cover a lot of electrician material), I took the first route when building my home solar PV system in stages (3 so far, 4th will wait until a plugin car is acquired). Sized the wire from main panel through production meter to subpanel for 50A, the largest system that might ever reasonably be installed. But put in a breaker fitting the size of what was actually installed at the time. 10A for the starter system, upsized to 20A with 2nd stage expansion, then to 40A with 3rd stage.

    This produced some minor rework at each stage, but no wiring replacement. The inspector had no problem with it, not the he would have noticed much.

    The choice might depend on how able-bodied or capable of the work you might expect to be when the upgrade might be needed. Already retired, I've done some advance wiring and other work now while I still can, so it won't (or shouldn't) be needed when I'm less able-bodied, weaker and more fragile. We never upsized our home, so don't intend to downsize until it's time for an assisted living facility. (That doesn't preclude packing up to move to a more retirement-friendly location.)
  3. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Apr 14, 2009
    Greenwood MS USA
    2012 Prius v wagon
    Step one, find the 'family' of your breaker box (service) and look at GFCI breakers for that family. If they don't have the size you are thinking of, you choices are simpler. My 'load center' is a QO by Square D, now Schneider Electric. That limits my choices.
    Since it is a 100 Amp service, running a two story, 5 bedroom house, 20 Amps is all I had to spare for my car.

    Your service will define what breakers you can employ, as well.

    I like the idea of 50 or 60 Amp wire and a 20 Amp breaker, if you Service can support that. For 50 Amps use Copper No. 6 wire, for 60 Amp use Copper No. 4 wire.

    Very common receptacles are NEMA 6-20R and NEMA 14-50R, many others exist. Anything over 60 Amps will need to be hard wired. You can safely use a 50 Amp receptacle on a 20 Amp breaker, just know you can't get 50 Amps out of it until you swap to the 50 breaker.

    @Rob43 Can wire adapters from what you have to what you need. Many people, including me, use his 240 volt adapter to the stock Toyota cable that cut charge time by two hours.
  4. john1701a

    john1701a Prius Guru

    Jan 6, 2004
    2017 Prius Prime
    Prime Advanced
    Yup, no big deal. We have our JuiceBoxes each on their own 40-amp line. They're capable of connecting to 50-amp (for 10 kW charging), but didn't see the need. Realistically, a sustained draw of 7.2 kW (that's 7.7 kW) from the 40 is plenty future-proofing. That will give you 200 miles in 8 hours.