Radiant Heat Boiler Wiring

[G-ManBart]

Okay, so I have an electric radiant heat panel on the way for my shop and want a sanity check.

The boiler is an electric unit rated at 12KW (240V). The literature lists a maximum 50A draw. They specify a 70 amp double-pole breaker and 4 gauge copper wire.

My problem/question is with the 4 gauge wire and what options I have. I have 2" conduit running out the top of my service panel into the attic over the shop. The wire will exit the conduit, cross the attic, then drop down through an interior wall into the closet/bathroom where the radiant heat panel will be mounted. The total run going up, across and down will be approximately 50ft.

As best I can tell my options are finding 4/2 NM-B (unlikely it seems), SE/SEU 4-4-6 copper, SE/SEU 2-2-6 AL, or go with #4 x 2 and #6 x 1 (ground) THHN in conduit across the attic, and down through the wall.

I looked briefly and haven't seen 4/2 NM-B. I really don't feel like running that much conduit for THHN and I'd like to save as much space in the conduit as possible, so aluminum is out. That pretty much leaves me with SE/SEU 4-4-6 which seems hard to find.

Am I missing anything obvious? Thx,

 

[pattenp]

If the SER cable is not buried/run within insulation you can use 6-6-6-6 at 65A at 75 deg. C. and are allowed to use the next standard size breaker which is 70A. If using NM you are stuck at 60 deg.C, so that means #4. If the SER is in insulation then it is also to be sized at 60 deg.C which will be #4.

Here's a place that carries both sizes of SEU by the foot.... https://shop.kendallelectric.com/ca...RE-and-CABLE/Copper-se-cable-seu/dept-1K0?a=1

 

[matt_i]

PVC conduit is pretty easy to run....you can install a rope when you assemble it and not even have to break out the fish tape, unless you are using LBs, etc.

 

[G-ManBart]

If the SER cable is not buried/run within insulation you can use 6-6-6-6 at 65A at 75 deg. C. and are allowed to use the next standard size breaker which is 70A. If using NM you are stuck at 60 deg.C, so that means #4. If the SER is in insulation then it is also to be sized at 60 deg.C which will be #4.

Here's a place that carries both sizes of SEU by the foot.... https://shop.kendallelectric.com/ca...RE-and-CABLE/Copper-se-cable-seu/dept-1K0?a=1

It's going to be above the current insulation, but I may eventually add blown in on top, so I think I'm going to stick with 4 gauge.

I can get 6-6-6 SER locally for $2.10 per foot, and it looks like online 4-4-6 will run me about $2.75 per foot. That's only about $50 more and I won't have to worry if I add insulation later...probably the smart way to go.