In article , "Bob" wrote:
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.

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


On the side of the heater it does state 240v but I believe this to be a
maximum applied voltage only.

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


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.

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

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.

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

So to recap, If I do revert to 240v the wire size must be 10 guage and there
must be 30 amp fuses?

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)