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"ime-share" a water heater circuit?

3739 Views 9 Replies 8 Participants Last post by  llninja
(1st post in these forums)
Just bought an off lease 2014 Volt, and have been pondering 240V EVSE options.

Whilst looking at my 30 year old breaker box and considering options, I was reminded of a long simmering project to put a timer on my electric water heater. And it occurred to me that most of the times when I would want the heater turned off would be good times to charge the car.

Which led me to doing some more detailed research into 240V DPDT timers.
Which led me to a couple quick hits on possible candidate timers.
- the GE 15207 ($25 on amazon)
- the Intermatic GM40AV ($60 on amazon)

Hmmm... No digging into the breaker box, just install the timer near the water heater and wire from the unused half of the timer's DPDT relays to the EVSE.

The part that has me scratching my head is the spec'd ratings of the timer relays.
I'll illustrate with part of the GE unit's specs:

Normally Open Contacts
40A Resistive, 120-277Vac.
30A General Purpose, 120-277Vac.
20A Ballast, 120-277Vac.
5.4A Tungsten, 208-277Vac.
720VA, Pilot Duty, 240-277Vac.
Normally Closed Contacts
30A Resistive, 120-277Vac
15A General Purpose, 120-277Vac
20A Ballast, 120-277Vac
360VA, Pilot, 208-240Vac.
NOTE: If loads are connected to both NC and NO contacts,
both contacts are derated to 67% of the above values.
Now obviously the water heater is a resistive load (in my case 4500W on a 30A circuit).
What "kind" of load does the EVSE+Volt charger electronics present?
And that 67% derating is a bit concerning...

Comments? Interesting idea? Total insanity?
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I contend that you don’t save anything by putting a timer on a water heater. Letting it get cold while it’s off only means you have to spend more energy to get the water warm again when the timer is on. Then there’s the convenience of having hot water any time you want it day or night and being able to charge you car anytime you want. The volt only needs a 16A EVSE on a 20 A circuit, but some people buy higher capacity EVSEs to future proof a bit. I have a 30A one just in case I buy something else that can use it. Alas, the stupid electrician that Bosch sent me put it on a 30A circuit, so I had to configure dip switches to max out at 24A so I don’t melt anything. Lesson learned. I’ll wire up my own 40A circuit if and when I buy a Tesla or anything else that can use more juice then reconfigure to use the full 30A.
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It doesn’t matter how old the panel is as long as it is safe. The question to answer is: does it have capacity to pull a 20-amp circuit to charge the car?

Messing around with Rube Goldberg switching is asking for fire to come visit. Use the thermostat circuit (the built-in switch) to modulate water heater use.

BTW. 20-amps is future-proof enough. All that is needed is ability to charge the average daily use. About 40 miles in the US.
Electricians in my neck of the woods use tandem breakers which are half-height so two separate circuits can be put it in the same slot in the breaker box.

I agree with the above statements that as long as the wiring is safe in the house, better to run dedicated circuits. If you're really in a pinch, you can go with one of the 'Quick 220' type options where you plug into two separate 110v outlets to make a 220v one but that is unwieldy and not a permanent solution.

Finally - if you were going to time-share anything, I'd probably look at either an electric dryer or an electric oven as they would probably get significantly less use than the water heater.
If you have the time and money and time to set up this relay and new EVSE outlet couldn't you just run a new dedicated wire from half-height CB's to this new EVSE outlet?
You don't have to Big Deal it and run the wires in the wall, do you? You can legally run wires outside the wall, correct?
I'd probably look at either an electric dryer

This was what I did with a 240V DTDP switch. When the switch is set to Voltec, the current goes to a new panel in the garage with a 20A breaker that feeds the EVSE. When the dryer is needed, switch gets set to Dryer and it gets the power instead. The EVSE has no power when the dryer is being used, but that's very workable in our house since the car is usually changed at night and dryer used during the day. It's worked great for over 6 years.

It was not the first though:
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There are automatic circuit sharing devices for this purpose
I vote for half-height breakers.
Space for breakers isn't an issue. I just like to explore all options before I choose one...

I also kind of like the idea of extending use of existing circuit(s) - that Leviton 30A DPDT switch had also caught my eye, though I hadn't considered applying it to the drier circuit (hmmm) - rather than adding circuits to my 150A service.

And FWIW - I live in a condo, so a certain amount of stealth and/or aesthetics is a consideration. Nothing insurmountable (I happen to be president of the association's board) but some approaches may be simpler than others.

As it so happens, I *have* an outside 110V outlet near my front door within the reach of the Volt's supplied EVSE (cord runs beside my sidewalk from front door to parking spot). Unfortunately it is a shared 15A circuit (the outlet itself is downstream from 1st floor half-bath GFCI receptacle) so I am stuck at 8A charging.

I have also considered personally adding a dedicated 240V 20A circuit - GFCI circuit breaker in box, and a Leviton 5842 DUAL-VOLTAGE outlet (single gang 5-20 and 6-20 combo) replacing the outlet in the existing box (i.e. stealthy approach). This would allow 120V 12A charging with supplied EVSE, and with something like the AV TurboCord later...

ANOTHER side of me, however, thinks I should push for adding a 30A hardwired (grumble NEC 625) EVSE (probably ClipperCreek) circuit, professionally installed on the wall near the front door, in order to establish a precedent for the association - costly in both time and money...

--ANYWAY-- getting back to original question...
There are automatic circuit sharing devices for this purpose
More I think about timer (i.e. relay) switched circuit sharing, the less appealing it seems. However I am curious what other 'automatic circuit sharing devices' are out there...

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There are automatic circuit sharing devices for this purpose
I know a guy who built his own custom box to allow 2 ev cars to share a single EVSE plug. You plug the j1772 into his box, it has 2 j1772s coming out, when both cars are charging it splits the amperage from the charging station, then when one car is charged, if\t gives all it can to the other. Not quite what the OP is looking for, but if this can be built maybe another similar contraption could be built for the water heater and EVSE. Alas, if it starts an electrical fire, good luck with the insurance company on the claim.

OP, the best solution is a dedicated circuit.
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