Electrical Wiring Hot Water Heater


All, I recently purchased a 20 Gallon Hot Water Heater (120V) 2000 Total Watts...... The National Wiring Code stated that it needs a 25 Amp/10 Gauge Wire.......
Doing the Math (WATTS = VOLTS * AMPS)
2400 WATTS = 120 VOLTS * 20 AMP (12 Guage Wire)
To my understanding 2400 WATTS is more then the Water Heater can pull
Could someone elaborate on why National Wiring Code would not allow me to use a 12 Guage Wire / 20 Amp Breaker?
Thanks
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In the USA the National Electric Code allows 80 percent of the capacity of the conductor which translates into 12 ga. is good for 16 amps or less

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What do you mean "Much Less Voltage Drop using a #10 opposed to a #12" ?
What would be the side affect for Hooking a #12 Wire pulling 16.7 Amps?
Could someone please explain "Continuous Load" and why a Hot Water Heater falls into this catogory.
Would the Hot Water heater always be pulling the full 2000 Watts or does it only pull 2000 Watts on the highest temp?
I have no problem running #10 Wire but I just ran #12 for a smaller Hot Water Heater and needed to return it because it was too small for its application (Washer/Dryer Room).
Thanks

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2000w is 16.7a. Since the circuit cannot carry more than 80% of maximum capacity, you would need a 21a circuit. Since there is no such thing as a 21a circuit, you need the next larger size. Even if you could get by with #12, why would you want to? #10 will give much less voltage drop and the price isn't all that much different.
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[snip]
Because a water heater is a "continuous load" as defined by the Code, and continuous loads are not permitted to exceed 80% of the rated ampacity of the circuit. For a 20A circuit, that is a maximum continuous load of 16A. Your water heater will pull 2000W / 120V = 16.67A, which is 83.3% of the ampacity of a 20A circuit. Thus you need at minimum 25A and 10ga wire. But don't knock yourself out trying to find a 25A breaker - you can run 30A on 10ga wire, too, and it will be much easier to find a 20A breaker.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Just my opinion and I'm not looking to start a "war", but American train of thought is go big or go home. We always overdo things. A lot of European influence is now invading American industry. Industries are now seeing that it is cheaper to buy foreign because they don't "Over Engineer" things(motors being a prime example). If you need a motor to do a certain amount of work and carry X amount of amps to do it, then that is what you buy. That is what it is rated for and guarenteed to do. American made products tell you this is what it can do, but put in a buffer in case you overdo it. Probably because of our legal system more than anything else. And Yes, if you don't follow the NEC then you will have problems with the insurance companies. It's digusting, but that's what we as Americans have asked for! Can it handle it? YES! Will the insurance companies pay the claim if there is a fire? Depends on how good a lawyer you have. And by the way I still drive a Ford!!! Haven't given in to foreign ......YET!

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The National Electric Code is written by the NFPA. That stands for the NATIONAL FIRE PROTECTION ASSOCIATION. They write other fire related codes as well. Most of the articles in that code were written because someone died. It is the code so someone does not get hurt or killed.
stretch
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The thicker the conductor, the less its resistance to current, and hence the less the voltage will drop due to the resistance of the conductor -- but #12 wire has a resistance of only two ohms per thousand feet to begin with. To state that #10 wire has "much less voltage drop" in your application overstates the case a bit.
In any event, you need a 25A circuit and hence #10 wire at a minimum anyway, so the difference in voltage drop between #12 and #10 is utterly irrelevant.

Possibly a fire. That's why the Code doesn't permit it.

"Continuous load: a load where the maximum current is expected to continue for three hours or more."
Most of the time, the conditions of use of a water heater would *not* fall into this category, but it certainly could.

The heating element is either on or off.

Well, then, run the #10.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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It seems mentally unhealthy to imagine the NEC is based solely on physical reality, vs the interests of wire manufacturers and insurance companies :-) The fusing current for 12 ga wire is 235 amps.
Nick
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wrote:

This statement is only partially correct. The 80% limitation refers to continuous loads, as defined in the NEC. The Code does not prohibit operating non-continuous loads at 100% of the circuit's rated capacity.

The NEC is based on the desire to avoid fire and electrocution hazards.

Which is, of course, totally irrelevant to the amount of current that can safely be handled by 12ga wire without, for example, igniting its insulation.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Well I caved - With a New Born Baby only days away and the reality that Insurance not covering my claim if there was a fire - I splurged the extra money and got 100Ft of 10/2 w Ground Copper Wire.... Strangly enough the Outdoor quality was cheaper then the indoor...... Go Figure
The Wire is run and connected but I have not flipped on the breaker to the Hot Water Heater yet. My plumbing skills have been tested and a small leak has developed on the Treaded Portion of the Hot Water Heater.... Of course I did not let the thread seal cure for 48 Hrs... I am hoping giving it time to seal will do the trick... Anyone have any view on Thread Seal and How long it usually takes to seal the thread?
Thanks you all for the input

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I'm guessing you compared the price of 100' of UF to 250' of NM...

If it's leaking, that means you didn't tighten the joint enough. Doesn't matter how long you wait, it isn't going to seal.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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