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Electrical Wiring

Electric Water Heater Time Clock

15 years ago

I have purchased a small home (built in 1970)with a 52" crawl space (concrete floor). The previous owner who lived alone had a small (40 gallon) electric water heater on a dedicated 30 amp (10/2) circuit controlled through a time clock to take advantage of a low power company electric rate during the night hours. I have replaced the existing water heater with another 40 gallon unit (I'm limited on height....40 gallon was as large as I could fit in). I have added another 40 gallon electric water heater on a seperate 30 amp (10/2) circuit to provide for a larger family.

My question is whether I can wire both electric heater circuits through the same time clock? The time clock is a Dayton Model 2E351B 24 Hour Dial Time Switch (SPST.) Can I simply connect both water heater units to the time clock in and out terminals, or will the combined amperage overload the clock switch or cause one of the panel circuits to provide power to both water heaters and trip the circuit breaker?

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Comments (3)

terribletom
15 years ago
NO! By putting two feeds from separate 30-amp circuits into the same switch, you'll do one of two things: (1) if the wires happen to be on opposite poles, you'll create a monumental short-circuit or (2) you'll be effectively running half of a 60-amp circuit in parallel on two #10 wires (disallowed in residential wiring).

And that assumes that the switch can handle 60 amps, which I doubt it is designed to do.

Definitely not a good idea.
terribletom
15 years ago
If you want to control two hot water heaters with the one timer in order to avoid having to keep two clocks in synch, you might be able to use a relay ("definite purpose contactor"), such as a Cutler-Hammer C25BNB230B.

You'd connect the load feeds of the timer to one hot water heater as well as to the control input terminals of the relay. The second circuit (for the second hot water heater) would get switched simultaneously with the first. Make sure that the relay is designed to accept 240V control input.

Done on a DIY basis, the parts-and-materials cost should be something in the neighborhood of $40, which makes it roughly comparable to adding a second timer. (You'll also need a box--say "6"x"6"x"6"--for the device.) One disadvantage is that the relay will draw a slight amount of current whenever the timer switch is on.
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stonehouse24
Original Author
15 years ago
terribletom...
thanks for the advice. As a solution, I purchased another separate time clock ...it is a TORK Model 7102 SPST 240V 40 amp switch with a 240V timer clock. The wiring had me baffled for a little while until I realized that I had to make up pigtails off my panel box line(10/2) to feed the timer switch circuit and the switch clock. Everything works, but I notice that when the timer switch closes and feeds power to my hot water heater, there is a low humming noise that seems to be coming from the 30 amp circuit breaker in my main panel box. . The humming stops when the TORK timer switch opens and breaks the feed to the HW heater. Is that normal or does that mean that I've wired something wrong?

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