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Old 02-21-2015, 06:48 PM   #1
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new wiring for electric hot water heater


I'm trying to figure out if it will be possible to have an electric water heater installed in my house, to replace a gas water heater. I'm trying to compare the electrical requirements of various heaters with the power presently available.

The electric clothes dryer, which I can give up, is connected to a circuit breaker labeled as 30 amps. This is a "double" breaker spanning the entire row. I have a house inspector's report which says the following:
"Main electrical panel . . . . 220 volt circuits"
"Sub-panel . . . . 110 and 220 (120/240) volt circuits"
Does this mean the total wattage for the clothes dryer circuit is 6,600?

The specifications for the AO Smith ProMax EJCT-20 water heater says:
"Element wattage" is 2500 for "standard 240V" and 6000 for "maximum 240V".
What is the meaning of "standard" and "maximum"?
If my electrical system only provides 220 volts, does that mean I can't use this water heater?

Also, how is the length of the wire from the breaker panel to the heater a factor?

And would there need to be a separate circuit for the controls on the water heater? There was no wiring to the old gas water heater.

I am just trying to understand better what my options are before I hire any professionals.

Last edited by eitnum; 02-21-2015 at 06:49 PM. Reason: typo
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Old 02-21-2015, 07:40 PM   #2
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#10 AWG required for a 4500w water heater, supplied by a 30 amp 2 pole breaker.
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Old 02-21-2015, 07:42 PM   #3
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220 and 240 are the same thing for a house. The actual voltage could be anywhere in between those two voltages.
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Old 02-21-2015, 07:47 PM   #4
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Nominal voltages are like the standard voltages that are produced by the utility company.
Such as 120/240, 120/208, 277/480, 347/600.

Lets say the nominal voltage to the building is 120/240. The Actual Voltage may be 115/235 or something like. The different in actual voltage and Nominal voltage can be caused by many things, such as voltage drop or the transformer tap, etc...The actual voltage can even be higher in value than the nominal voltage.
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Old 02-21-2015, 08:19 PM   #5
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stickboy1375,

What does "#10 AWG" mean?
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Old 02-21-2015, 08:50 PM   #6
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It is the wire gauge to use. AWG is just short for "American Wire Gauge".



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Old 02-21-2015, 09:13 PM   #7
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Quote:
Originally Posted by eitnum View Post
I'm trying to figure out if it will be possible to have an electric water heater installed in my house, to replace a gas water heater.
Gas water heaters are cheaper than electric to purchase, cheaper to run, and have a much faster rate of recovery. Why are you changing from gas to electric?
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Old 02-21-2015, 09:19 PM   #8
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Quote:
Originally Posted by eitnum View Post
stickboy1375,

What does "#10 AWG" mean?
Wire gauge is thickness of the copper wire to be used on the circuit. Smaller numbers are bigger wires, so as a general rule, #10 copper wire is good for a 30 amp circuit, #12 AWG is good for a 20 amp circuit, and #14 AWG is good for a 15 amp circuit.

Longer wires mean the resistance of the wire becomes more of a factor, creating a voltage drop if the wires aren't thick enough. I do not know how long a water heater cable has to be before a #10 would no longer be adequate, but it works for most residential installations.

Smaller wires are cheaper and easier to work with. Bigger wires allow for more expansion if the circuit allows it, allows a longer run, and you might save a few pennies in electric costs, because there is less resistance.

If you live someplace with high electric rates and have predictable hot water needs, though, you'll likely save money installing a hot water timer.
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Old 02-21-2015, 10:28 PM   #9
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IslandGuy,

I am also considering gas. I'm considering electric because the water heater may only be needed occasionally, I don't want to waste energy, and I figured electric would be easier to turn on and off.
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Old 02-21-2015, 10:51 PM   #10
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Thanks, Tom738.

Is there copper wire thicker than #10? Since the circuit will be 30 amps, I suppose there could be a problem with a long #10 wire. The wire will have to be about 42 ft. feet long--from sub-panel up to attic floor, along attic wall, across attic, and down to water heater closet floor.

Last edited by eitnum; 02-21-2015 at 10:52 PM. Reason: typo
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Old 02-21-2015, 10:57 PM   #11
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Quote:
Originally Posted by eitnum View Post
Thanks, Tom738.

Is there copper wire thicker than #10? Since the circuit will be 30 amps, I suppose there could be a problem with a long #10 wire. The wire will have to be about 42 ft. feet long--from sub-panel up to attic floor, along attic wall, across attic, and down to water heater closet floor.
You are fine at only 42' with 10/2 or 10/3.



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Old 02-22-2015, 04:06 PM   #12
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Thanks, gregzoll.

What's the longest (approx.) the #10 wire could be to handle 30 amps, 240 volts?

I've discovered my estimated 42 feet won't work, and it will have to be longer--up to 70 ft total. Due to my physical limitations I cannot get up into the attic to figure this out better.
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Old 02-22-2015, 05:14 PM   #13
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Quote:
Originally Posted by eitnum View Post
If my electrical system only provides 220 volts, does that mean I can't use this water heater?

A water heater designed to work off 240v will still work off 220v
it just won't get as hot.
Most people would not notice the difference,
as it's only 10%.

And are you sure your only 220v ?
mostly it's closer to 240v
have you checked with a volt meter ?

Last edited by dmxtothemax; 02-22-2015 at 05:21 PM.
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Old 02-22-2015, 05:17 PM   #14
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Quote:
Originally Posted by eitnum View Post
Thanks, gregzoll.

What's the longest (approx.) the #10 wire could be to handle 30 amps, 240 volts?

I've discovered my estimated 42 feet won't work, and it will have to be longer--up to 70 ft total. Due to my physical limitations I cannot get up into the attic to figure this out better.
You are fine. At this point you are over thinking the whole thing. Yes at 42' #10 wire will work just fine. No need to go with #8 or #6.

You would hardly notice a voltage drop at 42'.



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Old 02-22-2015, 05:53 PM   #15
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Quote:
Originally Posted by dmxtothemax View Post
And are you sure your only 220v ?
mostly it's closer to 240v
have you checked with a volt meter ?
we have a a thing in this country. Depending on your age, the nominal voltage quoted varies. Currently nominal residential voltages are 120/240. Years ago it was 115/230 and before that it was 110/220. I understand there were voltages even lower than that years ago but I'm not old enough to have been there. So, my father calls it 220 while it is actually considered to be 240.

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What's in a name? that which we call a rose
By any other name would smell as sweet;
the OP has 240 nominal and with the federal and state requirements, almost assuredly an actual voltage within 10% of that and likely even closer than that.
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