Plans for running new 8/3 NM-B service for oven

Question

I've been doing a lot of reading and planning for a run of 8/3 NM-B that is required for a new oven/micro combo in our kitchen remodel. We currently have 10/2. While I have quite a bit of basic home and other electrical experience, we want to be sure that we add this new run properly since I haven't done that before.

I've already started running the 8/3 and began about 1/3rd of distance by cutting out some ceiling and running one end down through an exposed HVAC return vent in the kitchen wall, through a few studs behind the fridge, and have wired it up to the installed oven next to there.

The other end of the wire is a lot more fun since the house is 2 story without attic access anywhere. From the opened ceiling above a walkway, we intend to bring the 8/3 down into 1" EMT behind some new large cove moulding for about 6 feet, then into the wall and down about 6ft to run through a fireblock and under our stairs (an unfinished and not exposed area that I'm having to cut into from garage to access). From there we'll go back up the insulated exterior garage wall on the opposite side of the stairs. At that point I'll add a surface mount 4x4x1.5 steel box, and then 1" EMT again along the garage ceiling and into the wall above the panel.

I know all about protecting the romex from damage (hence the EMT behind cove moulding and on garage ceiling), as well as stapling in the wall every 4' and securing the EMT to the ceiling, as well as most of the other basics.

My main questions though before we work on the rest of this:

1) Is it ok to have this cable non-continuous? It may be significantly easier to run this cable through some of the EMT bends in the garage by having a splice (with junction box and proper #8 wire nuts of course) in at least one place, but obviously continuous wire (and especially ground) is better. Additionally we bought a 125ft bundle but the total run should only be about 60-70ft, so that's a lot of extra to pull.

2) For the EMT to wall transitions in the garage, is it best to use a junction box? I imagine so because the connection from there to EMT can be very solid, and then the hole at the back of the junction box is centered and provides more distance from the edge of the wall surface to the wire (1.25" distance NEC rule).

3) For the ceiling to EMT (behind cove moulding) to wall transitions, should we use bent EMT pipe through the sheetrock with tightened Romex to EMT adapters on the ends within the ceiling/wall, or could we just use a straight EMT pipe and add nailing plates on the back of the cove moulding at the ends where the cable comes out and goes into the ceiling/wall? The latter seems easier since I don't have a 1" EMT bender (though realize I have to find one for the garage ceiling work).

4) We have to add a new 40A double pole breaker in the panel for this. Is it recommended to try and match the existing brand/model breakers exactly?

5) Should we upgrade this circuit to AFIC? We don't currently have any and I'm not sure of the usefulness only on a 240v to oven/micro combo.

Thank you!

Answer 1

OK here we go.

1) There is no violation to splice the conductors as long as it is "mechanically and electrically sound". Just remember that the splice is where things can go wrong, and they must be done in a junction box and accessible for maintenance.

2) It is alright to use a junction box for a transition. Just remember that when you are bring the romex out of the box with no conduit, the opening must be bushed. You can use a plastic snap in or a connector or a chase nipple with a lock nut.

3) In this case your are really not using the EMT as a conduit per say, but as a chase for the romex and to prevent damage to it. You can also buy pre manufactured 90's if you need to use them rather than expensing out a bender, and fitting them may be easier for the non skilled. See my remarks on bushing in 2). Also see your own remarks on the 1 1/2 in 2) as far as nail plates go. I prefer the overuse of them than take chances.

4) It's always a good idea to match the breaker with the Panel manufacturer although other manufacturers breakers will match up in certain panels.

5) There is no code requirement to use an AFCI with a range circuit.

Hope this helps, good luck.

Answer 2

Have as many splices as you want. If you look at how a wire-nut works, there is lots and lots of contact area between the wires and wires to nut, if you torque it down good-n-plenty. They're not a weak point. I use them all the time. Do your splices inside metal boxes as this gives you 'belt and suspenders' protection. Also, dismantle your first few with each size to make sure they are splicing as expected, and every time, give every wire a firm tug to make sure it isn't coming loose.

Don't use a 4x4x1.5 steel box for 1" conduit, for one thing it is unable to attach 1" conduit - it only has 1/2 and 3/4 holes! Use a 120mm (more commonly described as 4-11/16") deep box, it has 1" knockouts and twice the internal space. You'll thank me later. BTW big-box charges too much for 120mm's, try a proper electrical supply house, I've paid as little as $1.40 for em.

If you ever change ranges, you could find yourself behind the #8-ball because many ranges are 50amp and will require #6. Will 6/3 even fit in 1" EMT? You could find yourself redoing not only the cable but the conduit too. Or worse, just swapping in a 50A breaker and setting the house on fire.

Cable down conduit?

Anytime you're trying to pig-wrestle a multiconductor cable down conduit, you should always ask yourself: should I really be doing this?

When you are using the NM wiring method, you are sometimes required to armor the cable against damage, and there is nothing wrong with using conduit materials as armor. Heck you could run the cable in conduit the whole way if you really want to.

Since you are fitting a large portion of your route as proper conduit, with bends, fittings, boxes and splices, I have to ask -- is it feasible to locate an accessible junction box at a location not too bendy from where you must transition from cable to conduit? If so, it's far more practical to switch to the conduit wiring method at that point.

Then you can use single wires (THHN). With EMT the metal conduit qualifies as a ground, so you can get away with three #8 wires in 1/2" conduit. Through 1" conduit, that would be super easy, and we really like "super easy" when we don't own an electrician's truck full of pulling tools.

So...

1. Have as many splices as you like. Just do them competently, and undo one to make sure it's coming out right.

2. Six of one, half dozen of the other. I would use a junction box because I would want to make a NM to THHN transition there.

3. In that location you would only be using EMT as a shield, so whatever method is legal for the NM wiring method is fine.

4. You are obligated to use a breaker designed for your panel. That ends the discussion. Panel types are incompatible, even within brands. (CH/BR, QO/Homeline, Qline/GE, even Siemens has screw vs clip).

5. New work in conduit would be my lowest priority for AFCI breakers. Other circuits need it more. By the way, AFCI breakers will positively arrest any splice problems, if you're that worried about it.