I have a GFCI receptacle installed on the side of my house in a weatherproof box. It is on a dedicated circuit. I need another receptacle on the other side of the wall in the car port so my wife can charge her Prius. I don't want to run another circuit but I also don't want both receptacles on the same circuit because at some point they will both get used and trip the breaker (or become a fire hazard). So I'd like to install the new one and add a three-way switch on the hot side to switch between the hot feeds on the receptacles. Then only one can be in use at a time. See illustration below. The top is two receptacles in parallel and the bottom is two receptacles switched. The switch and 1st receptacle would be in a double gang weatherproof in the carport and the 2nd would be outside on the side of the house. enter image description here

Does anyone see a problem with doing this? Is there anything in the code which prohibits it? Any advice is appreciated.

  • Hello, and welcome to Stack Exchange. First, amazing diagrams! They show exactly what you're asking for. That said, I'm no expert, but I'd worry about running a Prius charger through a garden-variety three-way switch. – Daniel Griscom Mar 25 '18 at 23:25
  • How many taps are on this circuit already? As long as you arent exceeding the NEC its ok to add your next outlet in the same line. No need to switch it. If you are concerned about the circuit overloading, the breaker is there to cover that job. How likely are you to exceed a 75% with what you currently use the outlet(s) for? – noybman Mar 25 '18 at 23:45
  • Can you move the GFCI protection upstream, to a deadfront device or a GFCI breaker? – ThreePhaseEel Mar 26 '18 at 1:04
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    You can get a 20-A rated 3-way switch, but if you cut the power to a GFCI receptacle I believe it will trip, either when the power is turned off or when it is turned back on. This would be inconvenient and could drastically reducing the service life of the GFCI receptacles. I can understand your desire for frugality, but most people would install a separate 20-A circuit if there was a likelihood of users overloading a single circuit. – Jim Stewart Mar 26 '18 at 11:09
  • This is a user unfriendly concept. Do not do this. Put in a dedicated circuit for the Prius. Are you currently charging through a 20-A 120-V circuit? – Jim Stewart Mar 26 '18 at 11:16

This way of doing it is a little risky, because some GFCIs don't like to have their power interrupted on a regular basis.

A GFCI+receptacle combo device creates a zone of protection in its own sockets and anything downline that is attached to the LOAD terminals. Hot and neutral must feed symmetrically from LOAD. Ground bypasses the GFCI entirely (and that's important for it to work).

I'm not fond of your arrangement because aside from severing power to GFCIs, it violates a few of my "rules":

  • Don't put two GFCI devices on the same circuit
  • Don't put a GFCI device outdoors

So I would recommend installing one GFCI device that is upstream of the switch. Then use the output of the GFCI, via the 3-way, to feed two plain receptacles.

I would also use a 20A-grade 3-way. This won't cost $2.

enter image description here

Here I use brown/gray for hot/neutral in the protected zone, then I switch back to Romex colors just because I didn't want to redraw all that.

  • I like it. But something will have to be done to keep wifey from plugging the Prius into the (unswitched) GFCI outlet. - Is this a good use case for a blank-face GFCI? – A. I. Breveleri Mar 26 '18 at 9:36
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    @A.I.Breveleri -- it's precisely the kind of use-case you'd want a blank-face (dead-front) GFCI for – ThreePhaseEel Mar 26 '18 at 11:40
  • That works. Thanks for the feedback! I forgot to include power consumption numbers in my question. The Prius' built in 120V charger draws 12 amps for 5.5 hours at full power or 8 amps for 8.25 hours at reduced power. I'm probably overthinking this... between the GFCI and the 20 amp breaker, I'm sure its safe. – melodic_agony Mar 26 '18 at 13:14
  • @A.I.Breveleri The very nature of GFCI's is such a source of confusion for most people, that I was afraid if I opened up talking about a blankfront GFCI, I'd lose the reader. – Harper - Reinstate Monica Mar 26 '18 at 16:45

Just avoid the 3-way, breakers are there to avoid overload, just daisy-chain the next outlet and, at worst, circuit breaker will do its job.

Also most 'light' 3 way arn't strong enough to hold big currents so what risks to start a fire is the switch itself.


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