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I'd like to install a switch for the lower element of my water heater. I haven't even looked inside the water heater yet, but I'm a little confused about what the best way to go about doing this would be. When I open it up, I'm assuming that it's going to be easy to understand -- the element is probably just pigtailed off with wire nuts or connected to a bus. Getting the switch to work should be easy: shut off power, run the hot wire through a switch, reconnect power.

The hard part is making the whole thing look respectable. I've only come up with one option in that regard:

  • take apart the 240v receptacle, pigtail the +/- 120v lines
  • run one of the pigtails to a switch directly above/below the receptacle
  • run the two new lines (one being the switched leg) into another 240v receptacle box
  • drill hole in metal plate on top of water heater to accommodate the second cord
  • put the bottom element on the switched cord

That's a lot of work just to make the lower element switched, though, so if anyone can think of a more reasonable alternative, I'm all ears!

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Could I ask why you want this feature? –  staticsan Jan 22 '11 at 9:16

2 Answers 2

I really question the wisdom of switching just the lower heating element. Doing so is going to overwork the upper element. I assume you are trying to conserve electricity, but this tactic is not going to be a great benefit to you. The upper element is used as the "quick recovery" unit that gives the cooling water from the lower part of the tank a boost as cold water is added as the hot water is used. If the water cools too much in the tank and you call for hot water, the upper element will not be able to keep up until the temp of the majority of the water warms up. I would suggest an inline switch or timer controlling both elements to help conserve energy and insulate the tank as much as you can. If you are looking for short, small quantities of hot water , you may consider a 1 or 2 gal point of use electric tank, in line at the specific appliance. There are several models to choose from at the box stores for under $300.00 I might add, if you do try this switch idea, you will need to switch both 120VAC lines with a DPST,(double pole, single throw) 30amp switch wired with 10AWG copper. When you open the thermostat cover, you will find the lines are connected to screw terminals on the thermostat switches.

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The new question about a "ceiling box" made me come up with an idea for the two new boxes that I'll need. Space is cramped in my water heater closet. It was mildly cramped to begin with, and then I put two pumps, a heat exchanger, a controller, a sediment filter, pipes, and a 120V outlet in. Now that I'll most likely have to put a DPST switch and an additional 240V power cord, I was thinking that I could install those boxes on the ceiling.

Are there any special NEC requirements for doing so, especially when insulation is going to be above the box? I figure watertight boxes out to do the trick, no?

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