Water heater on 120V

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  #1  
Old 03-16-06, 09:35 AM
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Water heater on 120V

When Hurricane Isabelle plowed through our area a couple of years ago, I purchased a 5500 Watt generator which served quite well keeping our refrigerator and freezer up and running, as well as a couple of other "essentials." I do not have it wired into the house, it operates standalone with appropriate size extension cords to reach the appliances.

The one thing we ran out of after a couple of days was hot water. Well, my water heater is somewhat different that most, it only has one element, and it is 5500 Watts instead of the more common 2 X 4500 configuration. It would not make good sense to try to run a 5500 Watt water heater with a 5500 Watt generator. So, after careful consideration, I decided to hook the water heater up to a 120V, circuit. Since the resulting power requirement was only 1375 Watts, it took a bit longer to heat the water, but I had hot water after a couple hours.

My question is whether or not anyone has done this in a more permanent fashion, i.e. using a double pole/double throw switch in an external box, that would meet all code requirements. I would like for my wife to be able to do this, if necessary, if I happened to be on the road.

Thanks for your advice,
 
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Old 03-16-06, 10:00 AM
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> Since the resulting power requirement was only 1375 Watts,

How did you calculate this? You divided by 2 twice instead of once.


> using a double pole/double throw switch in an external box, that would meet all code requirements.

I see Code no problem with this.
 
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Old 03-16-06, 10:05 AM
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bolide,

Thanks for the reply. In effect, yes, I divided by 2 twice. The water heater element is a fixed resistance. Therefore, when you reduce the voltage by half, the current is also reduced by half. P=ExI.

Thanks,
 
  #4  
Old 03-16-06, 10:19 AM
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Randy, We were also affected the last 2 years by hurricanes. I'm running a 3500w element and continue to use 240v to drive it. Also, have a 5500w generator.
running 120v will work, but requires wiring rework to make that happen; not a big deal, but takes away from the yard clean up time
 
  #5  
Old 03-16-06, 11:38 AM
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Hello telecom guy,

When and if I have to buy a new water heater, I would probably end up buying one with the 2 element setup. Not many people even believe me when I describe the one I have. However, it does a very good job with the one 5500 Watt element. If I replaced that one element with a 3500, it would probably have difficulty keeping up during day-to-day use.

Anyway, my firm belief is that the probability of being affected by a natural disaster is inversely proportional to the amount of time and money we spend preparing for it. For example, I haven't had to use my generator once since Isabelle.

That said, I guess I just like to tinker, but I like to do things by-the-book. Plus, I would do almost anything to get out of yard work.

Thanks,
 
  #6  
Old 03-16-06, 12:15 PM
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> Not many people even believe me when I describe the one I have.

They are sold every day in small capacity tanks.

> However, it does a very good job with the one 5500 Watt element.

Better than 4500W.

> If I replaced that one element with a 3500, it would probably have difficulty
> keeping up during day-to-day use.

Correct.
 
  #7  
Old 03-17-06, 11:07 AM
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I have not done a detailed review of the code on this issue.

My gut feeling is that it would be code compliant to do the following:

Set up a suitably rated DP/DT switch, with the common terminals connected to the water heater, one throw connected to the normal supply conductors, and the other throw connected to a 'power inlet'. The power inlet is simply a wall mounted 'receptacle' with male prongs suitable for connection to the female end of an extension cord. Then you could just plug the water heater into a standard extension cord if necessary.

Here is a link for an inlet http://www.levitonproducts.com/catal...65D4D&pid=1208

-Jon
 
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