Hi
I have a construction heater rated at 4800W. it will be installed on a 30 amp double pole breaker. I had this installed in my previous house. and over there, it seems it had been installed using 12/2 wire (red, black and ground).
it worked for years but now I doubting if it wasn't done wrong

from what I understand the 30 amp breaker can take up to 7200W (30* 240) so plenty of room for the heater
Now, if using 12/2 wire then that means it can't take more than 20amps correct? and given the same math that would give me exactly 4800W (20 *240)

they had the red and black on either side and the ground on the bottom screw of the plug. but looking online today I saw that they used a 10/3 and brought red and black to either side and the neutral to third screw (bottom) where I had the ground before. I presume the ground wire would just be screwed to the box in this scenario?

see image in link
http://www.do-it-yourself-help.com/i...receptacle.gif

I had ripped out the heater, plug and wires when I left as my ex didn't need or want it.
can it go back with 12/2 or is it necessary to upgrade to 10/3?
if I don't have to install 10/3 that would save me some money as I have the old wiring...

thanks

 

Are you in Canada? In Canada they sell Red Romex, red, black, bare, for 240v. If in the US that isn't available. You use regular 2-conductor + ground NM-b (xx-2) and remark the white another color such as red or black.

A heater is a continuous load so the breaker must be 120% of the full load. A 25 amp breaker would be okay by code but the 30 amp breaker would be the usual. Cable must match or exceed the ampacity of the breaker so you need #10 even if you figure it at the lower 25 amps.

 

hi Ray.

yes, in Canada

so, 10/2 is what I would require. using the ground for the third terminal on the plug?

and that ground should first be screwed to the box then run to the plug correct? that's how I would do a regular plug, I presume this to be no different?

thanks

 

No, use the ground for the third wire on the receptacle, not plug. A plug is a male cord cap with blades.

 

hehe... yes, I often make that mistake... when I spoke of the plug I meant the receptacle

thanks

 

And not really the "third terminal", the ground terminal (green screw).

 

Slight correction, Ray, at least in the US, a heater circuit must be 125% of the load. Still would be a 25 or 30 ampere circuit breaker in this example as well as #10 wiring.

 

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