Electric water heater

I have an electric water heater (40 Gallon) that is hooked to 120V. 240V is run to a shut off switch (fused) just above the heater (3 feet away) but for some reason the installer ran 120 to the heater (black and white wires, the red is disconnected, and yes I can measure voltage). The main fuse panel has 2, 15 amp fuses for the circuit.
I was thinking of changing the water heater to 240v for the purpose of quicker recovery time. Is there a reason the person used only 120V? If I did this what would the fuse size in the panel need to be?
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I'd want a really good look at the water heater serial number plate, and also the elements. Makes me wonder if someone installed 115 volt elements. Were they the lower voltage, then 220 VAC would likely blow the elements.
Wattage equals volts times amps. If you're doubling the voltage, you should need half the amperage. Fuses are measured in amps.
There is no cost saving, you pay by the watt. (actually by the kilowatt hour).
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That's NOT the proper way to measure the voltage. You need to DISCONNECT those wires from the tank...turn off the double breaker first, of course...then turn the breaker back on...THEN check the voltage at the wires.
You might first want to check the wiring in the breaker box...to see if the wiring looks reasonable for the tank hookup.
Have a nice week...
Trent
Dyslexics of the world ... UNTIE !
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Hi Doug, hope you are having a nice day
On 14-Aug-03 At About 21:28:49, Doug Miller wrote to All Subject: Re: Electric water heater
DM> From: snipped-for-privacy@milmac.com (Doug Miller)
<rob@noway wrote DM> > When I say "only one is on at a time" , I mean only one element DM> in an > electric water heater is on at any given time. This I am DM> sure of.
DM> It's been a long time since I've had an electric water heater in a DM> house I've owned, so I could be wrong, but I don't think that's DM> correct.
He is correct here. first the top element heats the top of the tank then switches to the bottom element to heat the lower half of the tank.
-=> HvacTech2 <=-
.. "I bought instant water but I don't know what to add..."- s.w.
___ TagDude 0.92+[DM] +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ spam protection measure, Please remove the 33 to send e-mail
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As was already said...
If the fuses are matched correctly with the wire, you'll need to rewire the circuit.
Have a nice week...
Trent
Dyslexics of the world ... UNTIE !
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Read the other responses to your question as they provide some good insight.
If you have 120 volts powering 240 volt elements, it must take several hours for you to get warm water. There is a lot of resistance in those elements and hot water seems unlikely at 120 volts.

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I did measure across the 2 input wires at the upper limit switch on the water heater (it's a 2 wire system) and did read 120v.
I am pretty sure the wire is 10 guage but I will verify that.
The elements are 3000 watt and read 20 ohms. By my calculation (it's been awhile but i think I remember) 240 volts across 20 ohms is just under 3000 watts (2880) and since only one is on at a time.....the math works out.
On the side of the heater it does state 240v but I believe this to be a maximum applied voltage only.
As I said the water is fine once it is heated up but if I do use it up...it takes much of the day to get it back....estimate 4 to 5 hours. This doesn't happen very often since there are only 2 people living here most of the time.
I am not sure if there would be any reason to hook up 120 vice 240. It works obviously other than the recovery time. Any ideas other than installation error? It was installed 2 years before we moved in, which was 2 years ago.
So to recap, If I do revert to 240v the wire size must be 10 guage and there must be 30 amp fuses?
Thanks for all the help and the quick replies.It's piquing my curiosity more than anything.
Bob

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Yep. But what do you mean "since only one is on at a time" ?

No, that means it's supposed to be connected to a 240V source, not 120V.

It'll heat up a *lot* faster if it's connected to the correct source.

Obviously an installation error -- whoever installed it had no clue what he was doing.

240V across 20 ohms is a current of 12 amps. But you have two elements, hence 24 amps total. Therefore, yes, you need 10ga wire and 30 amp fuses or breakers.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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When I say "only one is on at a time" , I mean only one element in an electric water heater is on at any given time. This I am sure of.
The label states "maximum allowable rating" and states "240V" with 2 "3000 watt elements factory installed"
And I agree..it will heat up alot faster (4 times faster) with 240v vice 120v but is the only reason it would be hooked up to 120v is that the installer didn't have a clue?
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It's been a long time since I've had an electric water heater in a house I've owned, so I could be wrong, but I don't think that's correct.

For the third time, YES. The installer was incompetent. It's *supposed* to be connected to a 240V source. Think about it, man: you said yourself that the recovery time is 4 or 5 hours. That's absurdly long, even for an electric water heater. Doesn't that tell you that something is *wrong* ? What possible reason could there be for doing that deliberately? Why would anyone *want* to wait five hours for the water to warm up again?

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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On Fri, 15 Aug 2003 02:28:49 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

That is so. It heats the one end first (the top IIRC), then the other end when it reaches temperature.

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For this water heater it will draw 12.5A at 240V so you only require a 20A circuit. The smallest element I've ever heard of in a 240V model was 3600W, but even that will fit on a 20A circuit. I have a 5500W model, and that requires a 30A circuit. Water heater circuits must have an ampacity of 125% of the nameplate amp rating. If you have wires for a 30A circuit (i.e. 10ga copper), you can porbably install any replacement residential heater that you want. A 20A circuit will limit you to the ones with smaller elements.
The only reason I can think of someone would have done this was to "save energy". However, you will end up using the same amount of electricity to heat the tank back up. You only save when cold water starts coming out of the shower so you have to get out. Perhaps the previous owner had a person who liked to take forever hot showers and got tired of paying for it. Although a properly wired 20 gallon model would probably cure that too and allow another shower in 15 minutes.
-- Mark Kent, WA
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