DIY Home Improvement, Remodeling & Repair Forum

DIY Home Improvement, Remodeling & Repair Forum (
-   Electrical and Wiring (
-   -   5000 Watt Heater In Garage? (

Maladaahn 01-19-2009 09:59 AM

5000 Watt Heater In Garage?
Hello All!

I am installing a 5000 Watt 240 Volt Single Phase Heater in my garage. I currently have 110 in the garage running from my house through 1" PVC undergorund. I want to remove that, run 50 amps to a sub panel in the garage, and run the heater from that, as well as the 110 outlets, lights and garage door opener.

I have a 50 amp double pole breaker in my house panel for this run. The existing conduit in the wall for the old 110 run is 3/4" from the panel to a 4 x 4 box about 15' away. It then drops to 1/2" conduit from that box, runs about 3' down the wall, and feeds an outside box on the outside wall of the house. From the outside box, the 1" pvc runs underground to the garage, about 35' away.

The 3/4" conduit run above has 4 12ga wires in it now, 2 hots and 2 neutrals. 1 set feeds a couple of outlets and the other set continues on through the 1/2" conduit mentioned above to feed my shed.

My first problem is, if I use UF for the outside run, 6/3 will not fit into 1" PVC. However, 8/3 fits comfortably. Secondly of course is the 3/4" and 1/2" conduit capacity.

So, can I use 8/3 for this entire run? That would be standard 8/3 copper from the 50 amp breaker in my house panel, through the 3/4" conduit with the 4 other 12ga wires, through the 1/2" conduit with the 2 other 12ga wires, tie into 8/3 UF in the box on the outside wall of the house, and run through the 1" PVC to the garage. In the garage, the 8/3 UF would tie into standard 8/3 copper in a 4 x 4 box and run from there to the subpanel. From the subpanel, the heater would run from a 25 amp breaker and the 110 would run from a 20 amp single pole breaker.

I understand it would be better to run 6ga the whole way and lay new PVC, as well as run additional conduit in the house. But since that is not an option right now, it's 8ga as described above, and through the exisitng conduit in the house, or nothing at all. So I'm wondering if this will work, or is it completely out of the question. What about using a 45 amp or 40 amp breaker in the house panel instead?

Thank you in advance for your help!

glennjanie 01-19-2009 11:12 AM

Welcome Maladaahn:
You would be better off with the choice of nothing for now. The rig you have discussed is like playing with fire. The only trouble is fire is not play; life and serious injury are at stake here. Please hold off until you can run new conduit and proper wire.

triple D 01-20-2009 11:49 PM

get propane....ha...ha...
I have done some careful calculations. And I can tell you that you can leave the 3/4" pipe in place. But you must upsize your 1/2". The 4#12's are still o.k. with the two powers on 20 amp breakers. And you can fit 4 #8's thhn (copper) in there with them. You should have two blacks, one white, and a green. The only thing is you can only put the 8's on a 40 amp max. breaker. They may only run at 80% capacity in your sitituation. You should run thhn from panel to panel without junction in wire if at all possible. Good luck, hope I have been of help.:)

Maladaahn 01-30-2009 03:45 PM

Thank You!!!
Thank you both very much for your replies! I understand safety is always first. It sounds like the best compromise for now, aside from waiting, is to change the 1/2" conduit to 3/4" conduit and follow triple d's suggestions.

Thank you both again. I appreciate the quick response and sharing your expertise!


All times are GMT -6. The time now is 12:16 AM.