Page 1 of 1

Installing 7,500 Watt Heater In Garage

Posted: Tue Oct 23, 2018 6:58 am
by rchesterton
I've run 220 from my box into my garage to power a 5,000 watt heater using a 40 amp breaker as a dedicated circuit for that heater. The process was pretty simple.

Now I am helping my brother run a line from his box to his garage but he had to one-up me and purchase a 7,500 watt/240 V heater. He has 400 amp service to his house and plenty of space in his box for additional breakers.

My question is: What size breaker should I install and what size line should I run? I am thinking a 40 amp double breaker with 10-2 line. Is that sufficient?

Re: Installing 7,500 Watt Heater In Garage

Posted: Tue Oct 23, 2018 8:38 am
by emtnut
You will need to look at the specs in the manual for this.

40A breaker is extremely cutting it close, I'd be interested in what the mfr recommends.

"IF" this unit has '75˚' termination temperature, then #10awg is OK.
There is a good chance it's only rated at 60˚, which then would require #8awg. This should be listed in the specs, and marked on the connections in the heater.

Re: Installing 7,500 Watt Heater In Garage

Posted: Tue Oct 23, 2018 9:26 am
by rchesterton
It looks like they recommend 10 guage minimum with a max fuse size of 45Amps. I will use 8 guage to be safe - is that logical?

Here is the link to the manual: https://www.marleymep.com/system/files/ ... 95-000.pdf

So, if I am using a 45 amp breaker is that just going to fill a single slot in the box? I recall installing my own and using two breakers and 10-3 wire. I had the black going to one breaker and the red going to another, white and ground to the grounding bar. Is this going to be different? One single 45 amp breaker?

Re: Installing 7,500 Watt Heater In Garage

Posted: Tue Oct 23, 2018 6:02 pm
by emtnut
rchesterton wrote:
Tue Oct 23, 2018 9:26 am
It looks like they recommend 10 guage minimum with a max fuse size of 45Amps. I will use 8 guage to be safe - is that logical?

Here is the link to the manual: https://www.marleymep.com/system/files/ ... 95-000.pdf

So, if I am using a 45 amp breaker is that just going to fill a single slot in the box? I recall installing my own and using two breakers and 10-3 wire. I had the black going to one breaker and the red going to another, white and ground to the grounding bar. Is this going to be different? One single 45 amp breaker?
The 45A breaker needs to be a 'double pole'. It will take up 2 spaces, and you wire it as you did for your heater.

I took a look at the manual. The only place they mention #10 wire is in the text. The manual is for a few different heaters, so it doesn't give that warm fuzzy feeling !
If I was doing it at my own place, I would use #8 for sure.

Re: Installing 7,500 Watt Heater In Garage

Posted: Tue Oct 23, 2018 6:15 pm
by emtnut
Here is the same type heater. Take a look at page 2 of the manual under specifications.

45A breaker on #8 wire ;)

EDIT: might be handy if I actually posted the link :)
https://www.northerntool.com/images/dow ... /44740.pdf

Re: Installing 7,500 Watt Heater In Garage

Posted: Sat Oct 27, 2018 6:38 am
by rchesterton
Going to do this install this afternoon but I was only able to find a 40 amp circuit. I can order a 45 amp online but just want to double check before going that route that it is really necessary. The heater will pull a little over 31 amps wide open. If I were to use a 40 amp is it really cutting it that close? Safety is my top priority of course, so I will do whatever it takes to make sure I do this the right way even if it take a little longer. The way I figure it, if I am using #8 wire with a 40 amp breaker the worse thing that can happen is that it trips repeatedly. Then I would just have to increase amperage of breaker later on --- right?

Re: Installing 7,500 Watt Heater In Garage

Posted: Sat Oct 27, 2018 11:43 am
by emtnut
rchesterton wrote:
Sat Oct 27, 2018 6:38 am
Going to do this install this afternoon but I was only able to find a 40 amp circuit. I can order a 45 amp online but just want to double check before going that route that it is really necessary. The heater will pull a little over 31 amps wide open. If I were to use a 40 amp is it really cutting it that close? Safety is my top priority of course, so I will do whatever it takes to make sure I do this the right way even if it take a little longer. The way I figure it, if I am using #8 wire with a 40 amp breaker the worse thing that can happen is that it trips repeatedly. Then I would just have to increase amperage of breaker later on --- right?
I recommend ordering the 45A breaker.
The heater is 31.3A, but there is the blower motor in the unit as well.

Since you're probably there already, I would adjust the jumpers for a lower watt rating for now until the right breaker comes in.

The 40A breaker will probably never trip. What happens thou is that it will run hot. Over time that can damage the breaker, and in the event that something happens to the heater, the breaker may not protect the circuit.

I know, I know, I'm always the bearer of bad news :(

Re: Installing 7,500 Watt Heater In Garage

Posted: Sun Oct 28, 2018 9:33 am
by rchesterton
Thanks for all of the help so far. I followed your advice and will adjust accordingly when the 45 amp breaker comes in.

One more question...I used 8:3 wire. Black and Red to the breaker, white and ground to their respective bars in the box. But then I went to the heater and the manual only provides instructions for :2 wire. White and black.

What I did was used the black for L1 and the red for L2. Then, not pictured in the diagram, there was also a location between L1 and L2 that was the same type of terminal as the others except it was not connected to anything. I used that for white. Then ground screw for ground. See the image - I marked up where the third terminal was. This was just a picture I found online to show you what I mean.

Is that the correct wiring placement? The heater works with no issue. Just want to be sure I have it wired safely.

Re: Installing 7,500 Watt Heater In Garage

Posted: Sun Oct 28, 2018 12:05 pm
by emtnut
rchesterton wrote:
Sun Oct 28, 2018 9:33 am

One more question...I used 8:3 wire. Black and Red to the breaker, white and ground to their respective bars in the box. But then I went to the heater and the manual only provides instructions for :2 wire. White and black.

What I did was used the black for L1 and the red for L2. Then, not pictured in the diagram, there was also a location between L1 and L2 that was the same type of terminal as the others except it was not connected to anything. I used that for white. Then ground screw for ground. See the image - I marked up where the third terminal was. This was just a picture I found online to show you what I mean.

Is that the correct wiring placement? The heater works with no issue. Just want to be sure I have it wired safely.
The heater is 240V (not 120/240) so it only requires the Red,Black,and ground wire. You really only need #8/2.

I don't see on the diagram where you attached the neutral (white) ??
If it was an 'isolated' terminal block that isn't being used, that would be fine. If that connection point is attached to the heater metal casing, then technically that is a code violation and should be just capped off (in the panel and heater) with a small wirenut.

Re: Installing 7,500 Watt Heater In Garage

Posted: Sun Oct 28, 2018 12:35 pm
by rchesterton
The strange thing is that it does not show that third terminal on the diagram. The picture I included may be confusing because I just found it on the Internet. But that black terminal between the L1 and L2 terminals is completely isolated which is where I put the white wire into. If the safest thing to do is just terminated with a cap that’s an easy thing to do. But I believe the terminal was just touching Plastic housing and not a part of the actual heater. I will check that, and then to be on the safe side probably just pull that white out and cap it.