water heater wiring?

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Old 08-24-09, 08:46 AM
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water heater wiring?

I have an a-o smith water heater that is 80gal that has 2 3500/4500 elements in it. I moved in to this house about 10
years ago and this week I took the elements out to clean them and each 1 says 208/3500 and you turn it and it says 240/4500. I need to know if the wiring is correct they have a
double pole 20amp breaker with 12gauge wire, is this wiring correct, also are they running as 3500 or 4500 watts. The tank
has been running fine no breaker tripping or nothing I was just flushing the tank doing maintance.
 
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Old 08-24-09, 09:25 AM
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Originally Posted by drotti2004 View Post
they have a double pole 20amp breaker with 12gauge wire, is this wiring correct
No. It should be a 30A breaker with #10 wire.

also are they running as 3500 or 4500 watts.
If you're in a typical residential house 4500W. The dual marking means that the element will be 3500W if used on a 208V system such as those found in a commercial buildings or apartment buildings; or 4500W if used on a 240V system in a typical house.
 
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Old 08-24-09, 11:01 AM
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water heater breaker

I looked at the water heater itself the thermostat has its own circiut breaker of 40 amp so does that mean the double 20 amp in the electrical box is ok.
 
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Old 08-24-09, 11:19 AM
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No. The circuit is too small for the water heater.
 
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Old 08-24-09, 12:09 PM
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wiring

If it is incorrect its been like this for over ten years now so what will or could happen if I leave it this way , are the elements not putting out the full 4500 or are they operating under the alt 3500 watts. The wiring looks great no melting or burnt marks.
 
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Old 08-24-09, 12:17 PM
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It is incorrectly wired..period. Only one element at a time is energized, but each element draws 18.75 amps when on. That means the circuit is very near the max and is innappropriate for this usage. It may indeed operate this way..but it is incorrect.

You asked the question..sorry if the answers aren't to your liking.
 
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Old 08-24-09, 12:26 PM
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80 gal is large for an old house. The wiring may have been for a smaller water heater and not upgraded when a new, larger WH was installed. You need #10 wire on a 30a breaker.
 
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Old 08-24-09, 12:29 PM
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Wiring

There is a wiring diagram I found that shows different ways to wire it at the thermostat and to me it looks like its wired fo simitanously on but I will check it again. If it were simitanously on it would probably trip the breaker the way its wired now right?
 
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Old 08-24-09, 12:38 PM
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There is a wiring diagram I found that shows different ways to wire it at the thermostat and to me it looks like its wired fo simitanously on but I will check it again. If it were simitanously on it would probably trip the breaker the way its wired now right? also my heater runs on a timer in the morning hour for cheaper rates so mabey it is set for both elements to come on at the same time.
 
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Old 08-24-09, 12:39 PM
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Well true...I should have said "normally" only one at a time. And yes..if both came on, they should trip the breaker.
 
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Old 08-24-09, 12:52 PM
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wiring

well from what you said before about the 18.75 amps its the same idea because I have a double pole 20 amp breaker so that shoud be 18.75 per each side correct? no thats not right
look at my next message.
 
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Old 08-24-09, 01:04 PM
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wiring

from my calculations if you run both 4500 watt elements at the same time thats 9000 watts which would need a double 40 amp breaker right?
 
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Old 08-24-09, 01:35 PM
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I beleive if you take a look at 422.13 in the NEC it states water heaters are continuous loads and the branch circuit rating should not be less than 125% of it's nameplate. Most new water heaters are dual and only one element will run at a time. At 4500 watts 18.75 x 125% so you need a 30 amp circuit which should have #10 wire to it. If for some reason both run at the same time you would have 9000 watts 37.5 amps x 125% which you would put a 50 amp breaker with number # 8 or 6 wire. Depends on what type of wire you run. Good luck.

Jim
 
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Old 08-24-09, 02:34 PM
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Residential circuits and breakers are only rated at 80% for continuous use, meaning that a 20A circuit should only be used for 16A continuous. Yours is operating at ~19A.

Granted as far as code and safety violations go this is a pretty minor one, but ultimately the result is that the circuit is operating at a higher temperature than is appropriate. This can lead to premature failure of the breaker, wire insulation or splices.

It's not something I think should be repaired ASAP, but I would certainly put it on the to do list, especially if you're planning on servicing or replacing the water heater anyway.
 
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