Electrical question regarding shop heaters

[gnlman]

Hi. I have a 500 square foot shop(detached garage 100 amp service) that is divided into 2 parts. The back part of the shop (150 sf) is where my work benches are,  and the front part is 350 sf. I have a 4 kilowatt heater and I am adding a 1500 watt electric baseboard heater to the the front part of the shop which will stay set to prevent freezing all the time and turned up for comfort when I am working out there.

My question is this:

Presently I have the 4 kilowatt heater installed in the front part of the shop with #10 nmd90 and a double pole 30 amp breaker. The run to this heater is approx. 30 feet. What I'd like to do is feed both heaters from the one 30 amp breaker. The baseboard heater is 1500 watts, and 220 volts as well.
So what I am thinking is a 30 foot run (pull back original feed in attic) to junction box with #10, 2 foot run to 4 kilowatt heater, and run another line from the JB to the baseboard heater in the back shop. I am also wondering if I could use a smaller gauge wire to feed the baseboard heater as it will only be drawing approx 7 amps( 15 foot run)....I only ask as I'll have to go buy another length of # 10 wire if I decide or need to feed the smaller heater. I have lots of #12 and #14 kicking around......
I realize I could do this if it was on it's own breaker with no issues as it's only drawing approx 7 amps.....just not sure what might happen in the JB with the 4 kilowatt heater pulling more amps and having smaller wire in a marrett also pulling to the baseboard heater......

I am more inclined to just get the number 10 wire and feel safer about it all, but need to know firstly if I can feed both heaters from one breaker....
The smaller electric baseboard heater is also rated to 30 amp max.  I don't think I'm overfeeding the smaller heater should something happen the breaker should still kick......
I also realize I am right on the line for what I could be pulling from this breaker with both heaters on. While that may happen on occasion, I only heat the larger part on rare occasions.....but they could both be running at one time, so it needs to be safe.

I do have a bit of knowledge as I worked for a electrical contractor when I was younger, so know the basics and some code, just most of it's 20 year old knowledge.....lol
Thaniks for any and all help.
Greg.

 

[tjbnwi]

You're in Canada so the code may be different.

Without going into a lot of detail the NEC would allow 24 amps on a 30 amp continuous load circuit and 26.25 amps on a non continuous load circuit. From what you describe you have a NCL circuit. Your total draw is 25 amps.

The conductors cannot be smaller than the over current device rating allows. So 10 ga. is required through the entire circuit.

Tom

 

[mastercabman]

Do not hook both heater on the same breaker
Also,never use a smaller wire than what the breaker is made for.If you have a lot of 12g,why not use that for the small heater?(on a seperate 20 amp breaker)

Or you could end up with a 1 time very hot heater!

 

[gnlman]

Thank you for the replies
Not sure what I was thinking (other than the draw of the smaller heater) but yes that is correct......breaker protects the wire, they have to have the same rating.....yeeesh....lol
I believe we have the same 80 per cent rule here as well. Given that I cannot rule out that both heaters may at some time run to full potential (someone buys the place and doesn't know or family members go out and turn things on....) I think it's best to separate the 2 and be safe........

My motivation to try this was simply to save some space in the can as it's only 12 circuits and I want to do some other 20 amp drops for future needs. If I live on the edge and am overheating the breaker too often then my workshop may not have too much of a future.....lol

I will have to rethink my other plans and perhaps look at some mini breakers for space purposes should I need them. I don't have much in the way of stationary tools right now, but was thinking of the future and trying to make do with the box that I have.

As the Electrician I used to work with used to say....."nobody's house ever burned down because of a bad paint job, but if we do poor work it may happen"......words I've always remembered, and given the scarey things I saw in peoples homes, I've always had a great respect for electricity.......

Thanks again for the replies, and while I think it would work, I'll heed some old words from my past and run them separately.

Greg

 

[Rick Christopherson]

For non-continuous loads, you do have 100% breaker capacity on the circuit. This is an often misunderstood topic. It is there to protect the breaker from operating at 100% capacity continuously if the breaker is not rated for 100% capacity. In the event that the breaker is rated for 100%, then the 80% rule is completely removed and you can put 100% continuous load on that circuit. Non-continuous loads are permitted to reach 100% regardless of the breaker rating.

You don't need to worry about any of that because even if these heaters were continuous, you are still below the 80% rating of the circuit.

You can put the second heater on the same circuit, but as you already realized, you must keep everything at #10 wire size.

 

[gnlman]

thanks again for the reply Rick.
Hmmm I was dividing my watts by 220, and coming up with a higher number than 80 percent...I take it you divided by 240 (which is correct) which gets me under the 80 percent despite not needing to worry about the 100 percent potential....Yes very misunderstood (by myself as well) rule on breakers. Did some more reading and you are correct. I will be installing in the next couple of days and will figure out future needs and decide then if I spit them up or not.
Thanks again for all the info.
Greg.