Garage Heater Wiring Plan
My new-to-me Cadet #BH752 electric garage heater needs a new wall thermostat and 220v connection. The unit is 17-1/2" high x 16-1/2" wide x 12" deep and has a heavy gauge steel swivel/tilt mounting bracket. It will hang from the ceiling in one corner of the new shop. The unit draws 240v and 31 amps for 7.5 KW. The fan motor is a Dayton 1/50 hp. I bought it off Craigslist for $75 from a guy in Wasilla. Manufactured in 1983, it looks pretty much unused since 1985, the year it was disconnected. When I opened it up, I was struck by how much wiring it had. It took awhile, but I was able to figure out how best to wire it in.
Parts Used
- Double-pole, 220v, 4-wire, non-programmable thermostat w/ OFF setting (Honeywell Home CT410B, $18)
- #6 aluminum (SE wire), I'll only use 3 of the 4 wires; 35' feet needed ($25)
- 40A breaker
- Knock out connectors
- J-box w/ cover
- Single gang box for thermostat
- Flex conduit w/ connectors (~4 feet) w/ connectors
- Wire nuts
- Ground screw (?)
- Electrical tape
- Long wire staples
-NoAlOx shmoo
![](https://static.wixstatic.com/media/13658e_dc2d30b7b27f476e8205fb403fcf298f~mv2.jpg/v1/fill/w_147,h_81,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_dc2d30b7b27f476e8205fb403fcf298f~mv2.jpg)
I think this is how it should go, but change the wire gauge to #6 and breaker size to 40A based on the answers to these two questions...
![](https://static.wixstatic.com/media/13658e_1d47a127ea2647a1b641523101ef7404~mv2.jpg/v1/fill/w_147,h_69,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_1d47a127ea2647a1b641523101ef7404~mv2.jpg)
Question #1: Line power comes in at left into terminals 1 and 5. But I have two dangling wires (for a single pole thermostat that has been removed) which I don't know what to do with. In my plan, I'm bringing power from the panel through the thermostat (line voltage) to the heater. How to deal with these "extra" lines?
Answer: Connect the two wires for "Single Pole Thermostat" together w/ a wire nut.
Question #2: The heater draws 31 amps. Will a 30A breaker work or do I need a 50A breaker?
Answer: #10 gauge wire handles 30 amps, while #8 wire handles 40 amps. This unit pulls 31 amps, so I'll go with a 40A breaker and slightly oversized wire - #6 aluminum SE 4-strand cable in gray jacket. The take home lesson for me is that #8 gauge wire is kind of no man's land. #10 and #6 wire are very common and widely available, but #8 doesn't come in Romex (at least it doesn't near me) and is pretty much irrelevant. And while I can probably run separate #8 THHN stranded copper wire inside EMT conduit, that's a pain and a clunky solution. The #6 SE cable behaves like Romex (several wires in one jacket), is cheap, and is available everywhere.
![](https://static.wixstatic.com/media/13658e_5531c7226b40480ba7a96fb8144c206e~mv2.jpg/v1/fill/w_147,h_114,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_5531c7226b40480ba7a96fb8144c206e~mv2.jpg)
I used --> "4 CDR AWG 6 COMPACT AL. - AlumaFlex AA8176 Type SE Cable Style SER Type THHN 600V"
![](https://static.wixstatic.com/media/13658e_6f464debdb1b4b3cb41df139dfb1b1a2~mv2.jpg/v1/fill/w_147,h_95,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_6f464debdb1b4b3cb41df139dfb1b1a2~mv2.jpg)
Here's those two loose wires that I will wire nut together.
![](https://static.wixstatic.com/media/13658e_d2f707b5c7bd4c0694e9970f20fce8ae~mv2.jpg/v1/fill/w_147,h_122,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_d2f707b5c7bd4c0694e9970f20fce8ae~mv2.jpg)
Here's what the wiring actually looks like inside the heater with the cover off.
![](https://static.wixstatic.com/media/13658e_95653c30d3a249b3a140e2ee7b7e7ab1~mv2.jpg/v1/fill/w_147,h_113,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_95653c30d3a249b3a140e2ee7b7e7ab1~mv2.jpg)
Original wiring diagram from 1983. This sheet was inside the heater housing when I opened it up.
![](https://static.wixstatic.com/media/13658e_849b1afb8f44478091fcb73577da0e02~mv2.jpg/v1/fill/w_147,h_184,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_849b1afb8f44478091fcb73577da0e02~mv2.jpg)
![](https://static.wixstatic.com/media/13658e_63262649af814c6bb1f4a05764e37ef6~mv2.jpg/v1/fill/w_147,h_132,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_63262649af814c6bb1f4a05764e37ef6~mv2.jpg)
Here are the single-phase (black text) and 3-phase (red text) options. I'm following the single phase plan. Line numbers correspond to the terminals.
![](https://static.wixstatic.com/media/13658e_7de3e9104e8b4399a76ac840e64b71c0~mv2.jpg/v1/fill/w_147,h_120,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/13658e_7de3e9104e8b4399a76ac840e64b71c0~mv2.jpg)
Perspective sketch from the back of heater.