# What Size Wire For 220/4000 watt Heater



## stickboy1375 (Apr 28, 2012)

BigJim said:


> Question for one of you guys, I am installing a 220 wall heater and need to know if 12/2 wg shielded will be in code. It will be only about 25-28 feet of wire. If it is border line I will go with 10/2, don't want to burn the house down. This is one of the old fashion 3 tower wall heaters, I don't like them but that is all I can get right now.


Whats the wattage? You need to stay within 80% because it is considered a continuous load.


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## BigJim (Sep 2, 2008)

stickboy1375 said:


> Whats the wattage? You need to stay within 80% because it is considered a continuous load.


Sorry, it is a 4000 watt heater.


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## stickboy1375 (Apr 28, 2012)

BigJim said:


> Sorry, it is a 4000 watt heater.


#10 AWG is required.


20 amps x240 volts= 4800 watts x .8 (80% multiplier) = 3840 watts (too small) 

30 amps x240 volts= 7200 watts x .8 (80% multiplier) = 5760 watts (just right) 


{edited} To correct .8 multiplier, was originally .08


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## BigJim (Sep 2, 2008)

stickboy1375 said:


> #10 is required.
> 
> 
> 20 amps x240 volts= 4800 watts x .08 (80% multiplier) = 3840 watts (too small)
> ...


Wow, that was fast, you must have had your finger on the trigger.  There is a breaker already in place from the old heater so I will be good there. I like to have fell out when I took the old heater out, the ground wire just ran under the house and just laying on the ground not connected to anything.

I really do appreciate your help, 10 it is, thanks again.


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## brric (Mar 5, 2010)

BigJim said:


> Wow, that was fast, you must have had your finger on the trigger.  There is a breaker already in place from the old heater so I will be good there. I like to have fell out when I took the old heater out, the ground wire just ran under the house and just laying on the ground not connected to anything.
> 
> I really do appreciate your help, 10 it is, thanks again.


It's 4000/240 = 16.7 amps. I'd still use #10.
I think you may want to check your math. A .08 multiplier is not 80%.


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## stickboy1375 (Apr 28, 2012)

brric said:


> It's 4000/240 = 16.7 amps. I'd still use #10.
> I think you may want to check your math. A .08 multiplier is not 80%.


Typo on the .08, should have been .8 or 0.8 not .08 but regardless, the math I posted is the same, I just posted the wrong multiplier.

And he has no choice but to use #10, as #12 would be a code violation, and that is what the OP asked for.


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## Know A Little (Sep 29, 2013)

brric said:


> It's 4000/240 = 16.7 amps. I'd still use #10.
> I think you may want to check your math. A .08 multiplier is not 80%.



Haven't looked int eh NEC but when I did residential

Electric heater must be calculated at 1.25% or 

4000/240=16.7 x 1.25=20.875 amps


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## stickboy1375 (Apr 28, 2012)

Know A Little said:


> Haven't looked int eh NEC but when I did residential
> 
> Electric heater must be calculated at 1.25% or
> 
> 4000/240=16.7 x 1.25=20.875 amps


dude, 80% is the reciprocal of 125%....


125% = 1 \ 1.25 =0.8 or 80%


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## BigJim (Sep 2, 2008)

There is a whole lot more to electrical work than most folks know there is. I always subbed it out so I didn't learn much about the tech end of it. You guys are talking way over my head. 

I started to pull the wire this evening and my back went south so hopefully tomorrow. I was going under the house but it is too muddy so looks like i will go through the overhead.


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## stickboy1375 (Apr 28, 2012)

BigJim said:


> There is a whole lot more to electrical work than most folks know there is. I always subbed it out so I didn't learn much about the tech end of it. You guys are talking way over my head.
> 
> I started to pull the wire this evening and my back went south so hopefully tomorrow. I was going under the house but it is too muddy so looks like i will go through the overhead.


Just run the #10 and you are good, sorry about the back issues...


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## ctcarlisle (Sep 27, 2013)

stickboy1375 said:


> dude, 80% is the reciprocal of 125%....
> 
> 
> 125% = 1 \ 1.25 =0.8 or 80%


 

Stickboy: _What_?

No wonder Big Jim is confused; I am too. To say something about 'reciprocals' and then to say:

125% = 80% 

is weird, man.


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## k_buz (Mar 22, 2012)

It is...

80% = 4/5

5/4 = 1 1/4 = 125%


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## stickboy1375 (Apr 28, 2012)

ctcarlisle said:


> Stickboy: _What_?
> 
> No wonder Big Jim is confused; I am too. To say something about 'reciprocals' and then to say:
> 
> ...



Why is it weird? To find a reciprocal of a number, you divide that number into 1, if your number is a percentage, you must first convert that percentage into a decimal...

125% = 1 / 1.25 = 0.8 or 80%


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## Jim Port (Sep 21, 2007)

Stick is correct. You can take .8 of the breaker rating or 125% of the load. It does not matter.


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## Know A Little (Sep 29, 2013)

stickboy1375 said:


> dude, 80% is the reciprocal of 125%....
> 
> 
> 125% = 1 \ 1.25 =0.8 or 80%


No crap, WOW magic of math.:wink:


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## stickboy1375 (Apr 28, 2012)

Know A Little said:


> No crap, WOW magic of math.:wink:


It's very magical....


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## ccarlisle (Jul 2, 2008)

stickboy1375 said:


> Why is it weird? To find a reciprocal of a number, you divide that number into 1, if your number is a percentage, you must first convert that percentage into a decimal...
> 
> 125% = 1 / 1.25 = 0.8 or 80%


 
I know what reciprocals are, thanks. But nowhere does it say that 125% i.e, a number increased by one quarter is equal to that same number decreased by a fifth i.e. 80%. 

That's what that equation you wrote actually says; the second part is right that 1/1.25 = 4/5 = 80% - but 125% is not equal to 1/1.25...it's 1 x 1.25.

So:
1 x 1.25 = 125%
1 / 1.25 = 80%

What you're thinking of is 1 / 8 = 0.125 that's a reciprocal. But in fact, I don't think reciprosity has even anything to do with what we have here.


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## brric (Mar 5, 2010)

ccarlisle said:


> I know what reciprocals are, thanks. But nowhere does it say that 125% i.e, a number increased by one quarter is equal to that same number decreased by a fifth i.e. 80%.
> 
> That's what that equation you wrote actually says; the second part is right that 1/1.25 = 4/5 = 80% - but 125% is not equal to 1/1.25...it's 1 x 1.25.
> 
> ...


The reciprocal of 1/8 is 8. .125 is the decimal equivalent of 1/8, also the reciprocal of 8.


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## stickboy1375 (Apr 28, 2012)

ccarlisle said:


> I know what reciprocals are, thanks. But nowhere does it say that 125% i.e, a number increased by one quarter is equal to that same number decreased by a fifth i.e. 80%.
> 
> That's what that equation you wrote actually says; the second part is right that 1/1.25 = 4/5 = 80% - but 125% is not equal to 1/1.25...it's 1 x 1.25.
> 
> ...


Suite yourself....


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