Wire protection for underground line to detached garage

Question

I’m running a line from my 100amp main panel to a 40amp sub panel in my detached garage.

Can I run 8/3 NMD90 Romex through my the overhead joist system in my basement and out of the house through a hole in the block wall, then connect to individual sheathed 8ga wires in the 90 degree conduit box on the exterior of the block wall?

Pushing Romex through the buried (schedule 40 PVC, 3/4”) conduit underground seems difficult. I’d rather use individual wires inside the conduit all the way to the sub-panel, but individual wires through my basement joist system seems unsafe.

Is the 90 degree PVC conduit box the right place for that connection?

Also, do I need to run the PVC conduit through the block wall or is sheathed wire acceptable?

Answer 1

In Canada:

1. This corrugated flexible plastic conduit cannot be used as protection above or in ground where protection required, it's only allowed in concrete:

There may be variants that are allowed, and there may be other locations where it is allowed, thus you may see the blue variant a.k.a. smurf tube (Smurfs are blue) in basements.

2. Transition to THWN or NMWU can be in box outside against exterior wall. There is some discussion as to whether this is a matter of code or inspector tolerance.

3. Burial depth is 24in for NMWU direct burial or 18in in conduit or hard covered by e.g. 1x4 PT.

I am not an electrician but this is what I know from an electrician in Canada about a similar situation. I might have the subtleties wrong, but since this can be useful and debated in the comments, I am leaving it here as a supplemental answer rather than a comment.

Image from rona.ca

Answer 2

I doubt the USA/Canada differences are huge, here. NMD90 is evidently rated for exposed use dry or concealed used in dry or damp locations, so no wet locations. Exterior conduit is always a wet location.

The conduit should come through the wall, and you should make the transition from NMD cable to THWN wires in a box inside the building, not outside, or else run conduit the whole way and use THWN wires in conduit the whole way. Which might be easier than you imagine, if you can use corrugated flexible plastic conduit (smurf tube) in Canada, which I expect you can. Flexible metal conduit is also an option. If you have straight runs through the joists, you might not need flex, but many folks prefer flex in that sort of situation. If you have rodent exposure, choose metal.

Regarding ENT and the Canadian electrical code - most recent I could find without paying money was 2012, but here's the code language, and it does not appear to require concrete encasement as claimed in a comment.

Electrical non-metallic tubing
12-1500 Use Subject to the provisions of Rules 2-128 and 12-1502 to 12-1514, the installation of electrical non-metallic tubing shall be permitted(a)underground in accordance with Rule 12-012; and (b)in exposed or concealed locations.

12-1502 Restriction on use Electrical non-metallic tubing shall not be used unless provided with mechanical protection where subject to damage either during or after construction.

12-1504 Supports Electrical non-metallic tubing shall be securely fastened in place within 1m of each outlet box, junction box, cabinet, coupling, or fitting, and the spacing between supports shall be not more than 1m.

12-1506 Maximum number of conductors A tube shall not contain more conductors of a given size than are specified in Rule 12-1014.

12-1508 Temperature limitations (see Appendix B) (1)Electrical non-metallic tubing shall not be used where normal conditions are such that any part of the tubing is subjected to a temperature in excess of 75°C.(2)Subrule (1) shall not prevent the use of insulated conductors having temperature ratings in excess of 75°C, but such conductors shall not have ampacities exceeding those of 90°C conductors regardless of their temperature rating.

12-1510 Connections and couplings (1)Where lengths of electrical non-metallic tubing are coupled together or connected to boxes, fittings, or cabinets, fittings designed for the purpose shall be used.(2)Where lengths of electrical non-metallic tubing are coupled together underground, the couplings shall be applied using a solvent cement suitable for the purpose.

12-1512 Support of equipment Electrical non-metallic tubing shall not be used to support electrical equipment.

12-1514 Provision for bonding continuity A separate bonding conductor shall be installed in electrical non-metallic tubing in compliance with Rule 10-404.

2-128 Flame spread requirements for totally enclosed non-metallic raceways (see Appendices B and G) Totally enclosed non-metallic raceways installed in buildings shall meet the flame spread requirements of the National Building Code of Canada

Use duct seal (a grey non-hardening putty made for the purpose) to plug the conduit around the wires at the wall penetration, to reduce interior condensation.

The conduit outside will have to be buried at the code-approved depth (which I'm more familiar with the NEC then CEC version of - it varies with conduit type and protective concrete layers, or lack of same, typically), and may have to be schedule 80 in any locations considered exposed, assuming our codes are more similar than different. In many cases just using schedule 80 the whole way makes the most sense.