# How best to wire a 220V Heater



## middle.road (Feb 1, 2022)

In attempt to make sure I do this properly, I'm asking for assistance.
Neighbor gave me a 220V heater out of their MIL Cottage, and I would like to set up with 10-20' "pigtail" so I will be able to position in two different locations on the floor if possible.
_What GA wire would be best to use_?
I have a bunch of SO around, 12GA and 10GA.
There are (2) 220V taps in the shop, one is NEMA 6-15 wired to the panel with 10GA SO for a run of around 2' for my other ceiling heater.
The other tap is by the lathe - is it is an old time smallish 220 twist-loc that is wired with 12GA SO back to the panel for a run of about 20-25'

Thanks, _Dan


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## rabler (Feb 1, 2022)

That label is a bit odd, but if you take 7.5 kW, divided by 240 volts, you get 31.25 amps.  (A heater is going to be straight resistive, so the only reactive power is going to be for the fan motor, another .55 amps)  I'd want to run that on 8 ga, although you might(??) get away with 10ga for a short _cord_ but I wouldn't recommend it.    You don't say what your 220V outlets are using for breaker, but 12ga would typically be a 20amp circuit,  and 10ga might be a 30a circuit, neither which would not handle this thing.    Nema 6-15 is rated for 15 amps.  You'd need a 40A circuit and 8ga wire, and something like an oven/welder outlet (nema 6-50).


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## whitmore (Feb 1, 2022)

Instead of an extension cord, consider a pair of hardwired baseboard heaters; they are
standard construction items, relatively inexpensive
2kW heater wall mount
and you can choose the size for any convenient breaker and wire rating.


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## DavidR8 (Feb 1, 2022)

Isn't the 7.5Kw for 3 phase?


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## rabler (Feb 1, 2022)

DavidR8 said:


> Isn't the 7.5Kw for 3 phase?
> 
> View attachment 394669


That's why I said the label is a bit weird.  My read is that it will generate 5600 watts of heat at 208 volts, and 7500 watts of heat at 240 volts.   Resistive heat doesn't really use 3 phase like a motor, so I'm guessing it is "approved" for some sort of 3 phase wiring but that would imply 3 separate heating elements?   

editted to add:  You could have 3 heating elements, wired together in  parallel for single phase, or separately between legs of 3phase, and you'd get the same KW figure.


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## DavidR8 (Feb 1, 2022)

rabler said:


> That's why I said the label is a bit weird.  My read is that it will generate 5600 watts of heat at 208 volts, and 7500 watts of heat at 240 volts.   Resistive heat doesn't really use 3 phase like a motor, so I'm guessing it is "approved" for some sort of 3 phase wiring but that would imply 3 separate heating elements?


I thought that was odd too. 
But like Mr. Mom says "110, 111, whatever it takes!"


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## rabler (Feb 1, 2022)

Both of values 208 volts, 5600 watts,   and 240 volts, 7500 watts correspond to a resistance of 7.7 ohms.  (P=V^2/R)
So that tells me I'm reading that right.


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## middle.road (Feb 1, 2022)

Yeah, I saw 'Kilowatts' and that was outside of my knowledge level...
So it pulls 'one heck of a load'. figures.
I have only 8GA running from the panel in the basement to the sub-panel in the shop, so this is a no-go, it would appear.


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## rabler (Feb 1, 2022)

P.S.  That thing is going to kick out a good amount of heat.  And your power bill will remind you of that $$.


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## RJSakowski (Feb 1, 2022)

OTOH, If you were to run it on 120 instead of 240, the current draw would be half  @ 16 amps and the power would be 1/4 or around 1900 watts or 6,500 Btu/hr..


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## rabler (Feb 1, 2022)

RJSakowski said:


> OTOH, If you were to run it on 120 instead of 240, the current draw would be half  @ 16 amps and the power would be 1/4 or around 1900 watts or 6,500 Btu/hr..


Or, if it truly has 3 separate elements, just run one element and the fan motor on 220v  for a little over 2kw at roughly 10amps.

or get really creative and run two elements in series, in parallel with the third.   Ballpark 15 amps and 3.5kw heat at 220v

A switch would even let you select between those two..


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## Hawkeye (Feb 1, 2022)

The only problem with the lower voltage would be what the motor would be doing. Swap out to an equivalent power 120 volt motor (less that .1 HP) and you've got a winner.


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## ddickey (Feb 2, 2022)

You need 8 gauge wire for that heater. The way I read that label is you can run single or three phase too.


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## RJSakowski (Feb 2, 2022)

Hawkeye said:


> The only problem with the lower voltage would be what the motor would be doing. Swap out to an equivalent power 120 volt motor (less that .1 HP) and you've got a winner.


Separate out the fan  wiring and run the fan on 240.  Run the heater elements on 120.


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## woodchucker (Feb 2, 2022)

RJSakowski said:


> Separate out the fan  wiring and run the fan on 240.  Run the heater elements on 120.


so the heating elements are spec'd for 208/240... I get you can run it on 120, but why, the amps would go up?


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## strantor (Feb 2, 2022)

I am leaning the same direction as others, in suspecting there are separately connectable elements that could be wired in a number of different unorthodox series/parallel ways to suit your needs. But to be certain could you remove the cover and post pictures of the inside? And if you have a multimeter measure the resistance of the coils.


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## WobblyHand (Feb 2, 2022)

woodchucker said:


> so the heating elements are spec'd for 208/240... I get you can run it on 120, but why, the amps would go up?


No, the amps would be reduced.  Ohms Law.  E = I x R.  (E [volts], I[amperes], R[ohms])  The resistance is fixed, at say 7 ohms.  

Solving for I, we have I = E/R = 120V/7ohms = 17A.  Power = E x I, or E^2/R or I^2 x R.  P = 120V x 17A = 2040 watts. (2.04 KW).  So you will get less heat running at 120 volts than 220.  But the current will go down as compared to the 220V case.


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## Bi11Hudson (Feb 2, 2022)

strantor said:


> I am leaning the same direction as others, in suspecting there are separately connectable elements that could be wired in a number of different unorthodox series/parallel ways to suit your needs. But to be certain could you remove the cover and post pictures of the inside? And if you have a multimeter measure the resistance of the coils.


Looking at the nameplate, I concur. Being 1 *or* 3 phase leads me to *believe* there are 3 elements that can be wired in pure Shunt for single phase or in Delta for 3 phase. If the elements were wired 3 phase Wye (Star), only 2 elements would be used for single phase. That would leave one element as a spare. If it is wired Wye already, the heaters will be rated 120 volts each. Connecting only two legs and insulating the third will cut the draw down by 33%.

The bottom line is that  there are several *IFs* floating around. We need to know how it is connected and what the ratings are per element. Industrial elements will have the ratings engraved *somewhere* on the element. The KW ratings for 240 Vs 208 would lead one to believe they are pure resistive, a good thing for non-conventonial wiring.

OTOH, purely resistive is going to be expensive heat. I live down south where it wouldn't take much heat to work. Just a couple KW to keep my feet warm. I wouldn't be able to survive in Alaska. Get us some ratings and homebrew wiring diagrams to work from. We will make this thing usable.

.


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## strantor (Feb 2, 2022)

Bi11Hudson said:


> The bottom line is that  there are several *IFs* floating around.


Exactly. A picture is worth 1000 speculations.


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## middle.road (Feb 2, 2022)

Yeowser, I am so glad I asked.
I'll tear down the unit (once I get a bench cleared off) and get some picts and take some measurements.

Thanks all for responding.


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## rabler (Feb 2, 2022)

middle.road said:


> Yeowser, I am so glad I asked.
> I'll tear down the unit (once I get a bench cleared off) and get some picts and take some measurements.
> 
> Thanks all for responding.


Dan,
Since there are several options, I think the other important question is what do you want to achieve?  Are you trying to replace the existing electrical heat?  Add another heater?  If you're trying to add another heater, what is the breaker size and wire size for the supporting circuit?  Or are you looking to add a circuit?


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## stupoty (Feb 2, 2022)

WobblyHand said:


> No, the amps would be reduced.  Ohms Law.  E = I x R.  (E [volts], I[amperes], R[ohms])  The resistance is fixed, at say 7 ohms.
> 
> Solving for I, we have I = E/R = 120V/7ohms = 17A.  Power = E x I, or E^2/R or I^2 x R.  P = 120V x 17A = 2040 watts. (2.04 KW).  So you will get less heat running at 120 volts than 220.  But the current will go down as compared to the 220V case.



I think he (RJ Sakowski) means the motor amps not the heating element.  Hence running the motor at the high voltage and heating elements at lower.

I believe a simplified explanation would be that it's trying to draw the same power and to do this the amps go up , which can happen due to being an inductive load.

(I feel I may have over simplified or be slightly inaccurate  )

Stu


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## middle.road (Feb 2, 2022)

rabler said:


> Dan,
> Since there are several options, I think the other important question is what do you want to achieve?  Are you trying to replace the existing electrical heat?  Add another heater?  If you're trying to add another heater, what is the breaker size and wire size for the supporting circuit?  Or are you looking to add a circuit?



I was thinking of just having 'space' heating when I'm out in the garage and am not going to try to heat the entire shop.
There's no insulation in the walls. Ceiling yes, walls nada. I've been using a propane heater this season, but with the cost of propane. . .

Shop sub-panel is a kluge. I should have re-wired the entire garage and insulated it when we were moving in, however there were pressing issues with the house itself that I had to remedy.
It's a detached garage, that was supplied by an underground 10ga Romex to a (8) slot sub-panel, until we dug up the septic several years ago.
The Romex was running out of the basement, under a concrete patio then 10' to the garage.
When that got messed up, I replaced it with a run of 8ga SO under the attached covered porch deck to the garage.
30A at the main panel in the basement out to the sub panel's 30A cut-off breaker, and from there I run 15A or 20A breakers.
The lathe and the ceiling heater are on the same 20A circuit, so I make sure never to run both at the same time.
(7) circuits total currently, (2) 220V, (5) 110V. 24' x 24' garage.

This is the ceiling heater I have up currently:



It's not really a good source since it's mounted up on the 8' ceiling, doesn't get down to 'knee' level.


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## rabler (Feb 2, 2022)

Any reason you don't just put the other heater on the floor?

That heater is drawing just a bit over 20A, so it is actually quite a bit more load than you should technically be running on a 20A circuit.  Breakers aren't always exact, but I'm surprise you haven't tripped your 20A breaker running that.  It really should have a 30A circuit.  Anyhow, you're not going to be able to get MORE electrical heat than that (without rewiring), so all that is left is getting it where you want it.


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## middle.road (Feb 2, 2022)

rabler said:


> Any reason you don't just put the other heater on the floor?
> 
> That heater is drawing just a bit over 20A, so it is actually quite a bit more load than you should technically be running on a 20A circuit.  Breakers aren't always exact, but I'm surprise you haven't tripped your 20A breaker running that.  It really should have a 30A circuit.  Anyhow, you're not going to be able to get MORE electrical heat than that (without rewiring), so all that is left is getting it where you want it.


No not really. I put in the NEMA 6-15 receptacle above the sub-panel with leftover 8ga close to the ceiling and then mounted the TPI to a rafter.
I was keeping it short, thinking along the lines of a clothes dryer
I really had not thought about taking it down and putting a longer pigtail on it until yesterday when the neighbor gave me the other.
I just ran out to the shop and checked the circuit. The heater is on two 30A breakers. That can't be good. 30-30-30?
I do believe that I need to re-work the sub-panel.


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## rabler (Feb 2, 2022)

middle.road said:


> The heater is on two 30A breakers. That can't be good. 30-30-30?


Not ideal and may not be to code, but I’d be more worried that I don’t think SO cable is intended to be used as a feeder for a sub-panel.


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## RJSakowski (Feb 2, 2022)

To clarify, if the resistance is 7.7 ohms, it would draw 31.2 amps at 240 volts.  Running on 120 volts, the current draw would be 15.6 amps.  The resultant power would be 120 volts  x 15.6 amps = 1870 watts.  The fan motor would have to be run on 240 volts.

This calculation is made with no knowledge of the internal configuration.  If it is indeed wired for either single or three phase operation, in all likelihood, there are three separate heating elements and one or two of them could be disconnected to reduce the current draw with a corresponding decrease in heat output.

One consideration is that there is a significant increase in resistance as the heating element heats up so the current draw at 120 volts will be more the half that at 240 volts. The actual draw will be dependent on thermal properties of the heater and the actual alloy used for the heating elements.  Nichrome is a commonly used alloy for heating elements.


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## middle.road (Feb 3, 2022)

rabler said:


> Not ideal and may not be to code, but I’d be more worried that I don’t think SO cable is intended to be used as a feeder for a sub-panel.


No probably not. I believe it is to only be used for temporary feeds. This hunk came off a construction site where it provided power to the site.
It ran from the mains to a temporary outdoor panel, and also fed the trailer, which had 220V HVAC.
It came down to a matter of cost at the time. I had this on hand. 8ga at the BigBox retailer would have ran ~$260. It wasn't in the budget and I needed power in the shop to run the equipment to repair the house - Catch22. I didn't want to run a bunch of extension cords out of the house into the garage.



RJSakowski said:


> To clarify, if the resistance is 7.7 ohms, it would draw 31.2 amps at 240 volts.  Running on 120 volts, the current draw would be 15.6 amps.  The resultant power would be 120 volts  x 15.6 amps = 1870 watts.  The fan motor would have to be run on 240 volts.
> 
> This calculation is made with no knowledge of the internal configuration.  If it is indeed wired for either single or three phase operation, in all likelihood, there are three separate heating elements and one or two of them could be disconnected to reduce the current draw with a corresponding decrease in heat output.
> 
> One consideration is that there is a significant increase in resistance as the heating element heats up so the current draw at 120 volts will be more the half that at 240 volts. The actual draw will be dependent on thermal properties of the heater and the actual alloy used for the heating elements.  Nichrome is a commonly used alloy for heating elements.


I need to get this puppy opened up and see what's inside.


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