Electrical Conduit Question

Guys,

I'm helping a family member completely rewire a 100 year old house, getting rid of all the old knob & tube, service upgrade, etc. - bringing the entire house up to current code. Permits have been pulled for everything. My question - I'm venturing into a situation I've never had to deal with before & would appreciate your guidance. Here's the situation:

In the basement, the first 2 main floor joist spaces across the entire front of the house are an HVAC cold air return. We pulled out all of the old k&t that was run into & through the cold air duct & up into that wall space feeding the main floor receptacles and switches on that front wall. We replaced those runs with armored cable (MC) between a metal junction box located prior to the cold air return in the basement, through the return & to the receptacles.

My last challenge is that he has some 120v landscaping lights running along the front porch steps that are hardwired in and totally against code as-is. There's a cold room located under the porch that I can run the new circuit through to get the new circuit & plug where it needs to go, but in order to get into the cold room, I need to also run through the same cold air return mentioned above. What I would like to do is run some 3/4" EMT from a metal box in the basement, cross horizontally through the cold air return, pop through the exterior wall under the porch to the cold room where I would put a PVC LB and then transition to 3/4" PVC (above grade) for the rest of the run along the cold room's walls, under the porch, and eventually pop out with a weatherproof, surface mounted receptacle box. Then he can pickup some low voltage lighting to replace the lights. Was planning to pull 14ga THWN for the entire run, GFCI for the exterior plug.

Question: 1) How do I transition from metal EMT to PVC at the PVC LB? Is there a connector of some sort that does that transition? Never had to deal with this situation before. 2) Is this how you would do this, or would you just run EMT for the entire run? I was concerned with the metal conduit, being outside, rusting, waterproof, etc. (granted, it's under a porch) 3) Other option I was thinking about is running 14-2 UF in EMT through the cold air return, and then just running the bare UF cable under the porch through protected areas, just like you would romex/NM.

 

If the majority of the run would be metal EMT, I see no reason to transition to PVC conduit at all. If you do want to transition to PVC conduit, install a EMT compression connector on the EMT and thread a PVC female threaded adapter onto the threads of the EMT connector and continue on with PVC conduit. You'll have to pull a ground wire and properly ground each metal box and each device for the entire conduit run. Or.....you could install a metal junction box at the end of the EMT run and continue from there with PVC conduit. You'll need to pull a ground wire either way.

 

Looking at your location, you weather is about the same as ours. EMT will eventually rust, but it will take 20+ years.

 

I'm not sure what installing MC gained you. Is there a reason you didn't just hold all wiring below the joists and the return air duct?

 

I'd need the EMT to go about 4' horizontally through the cold air return and penetrate the outer front wall plate (which gets me into the cold room, under the porch). From that penetration point, it would be another ~15' to where he wants the plug.

Yea, I stopped by HD tonight after posting above and that's basically the solution i came up with. Only difference is that I was going to use a 3/4" PVC LB once I penetrate out under the porch to do the EMT-to-PVC transition, since I need to do a 90* turn anyways. And, yes, I was planning on pulling 3 conductors the entire length - THWN 14ga.

Yes, SE MI. That's why I'd prefer the PVC, even though this conduit probably will never be directly exposed to the elements.

We did that in the other areas of the basement - staying out of the cold air returns entirely, and building a small, shallow "bulkhead" or "raceway" to protect the NM cables that we ran underneath the joist space. The problem here is that the home's main floor front wall is directly above a double joist space cold air return in the basement. They literally popped holes vertically through the floor into the front wall, all of which is contained in the cold air return. There's no way to get into the front wall from the basement w/o entering that cold air return space, and running up that wall. My understanding of code is that while it's ok to cut across a cold air return with NM, though preferred to go below with the bulkhead/raceway, you cannot run vertically within a cold air return with NM. Has to be conduit or MC.

I don't know - maybe the front wall penetration holes wouldn't officially be considered cold air space going vertically (I'll fire stop calk all of them), even though they're all within that return space.

 

I think you made a good choice with both the MC and the firestop.

 

Electrical folks, what's your experience with this:

With plumbing tapered-thread fittings, it is often recommended to convert to a metal coupling so you can use a male-threaded plastic fitting. The reason for this is that the male-threaded metal pipe would otherwise push out on the female-threaded plastic fitting, eventually cracking it.

I am guessing this is not as much of a concern with electrical since you're not using pipe dope or even trying to tighten it enough to waterproof it, but the tendency would be to make it snug, and maybe snug enough that the fitting would eventually crack.

 

I don't think there will be any issues. The OP could also use a female threaded LB.

 

There is an alternative to use a PVC male threaded adapter with a heavywall galvanized coupling between the PVC adapter and the EMT connector, but that creates another problem. Heavywall couplings are U.L. Listed to join lengths of heavywall conduit together and not for being used as an adapter between EMT and PVC conduit. Regardless, I would run all EMT and forget transitioning to PVC.

 

Interesting. It sounds like you're saying that the front exterior wall is framed with its bottom plate resting on flooring material, and not on the front rim joist. Is that right?

Also, is the basement finished or unfinished? Could the return air flow travel in ducts hung below the floor joists? So that wiring, piping and insulation could occupy the space between the joists?

 

Thanks for the help everyone.

Mmmm - I would say that the main floor wall is framed over the rim joist in the basement, but the only way to get up into that wall from the basement is a diagonal hole drilled up from the first main floor joist space (adjacet to the rim joist) up into the exterior wall. I'll be over there tomorrow - I'll take a picture.

Partially finished, but the ceiling is open. That would be an option, but I don't think he wants to get into the additional cost of moving HVAC runs. Also, since the house is older, it's only ~7' ceilings in the basement to begin with... I'm only 6' and I have to walk around hunched over most of time to avoid the main structural beam and other HVAC runs that drop down.

 

Understood. I'm wondering whether, in Michigan, the savings in heating costs would offset the costs of relocating the return air ducting and installing an appropriate level of insulation below the first floor.

Hmmm - I'm wondering whether one of these might help:Klein Tools 9/16 in. x 54 in. Screw Point Flex Drill Bit.

Looking forward to seeing the pictures.