Using ent conduit “smurf tube” for 4 4awg wires

Question

I’m currently running power to my garage. I have to special order 1.5” flexible metal conduit. So I was going to just use some one inch stuff. I didn’t want to buy 25ft. So I found smurf tube. Can I use that for my flexible conduit from the outside of my house to my box inside my house? I’ve tried to find any code on it. I don’t go over the fill limit. But I got told that that’s not conduit that it’s only for data and low voltage. I’m using 29” of it from where it comes through my wall to my box. Any info would be great

Answer 1

ENT is A-OK for residential mains wiring

Actual UL listed ENT ("smurf tube") is a perfectly fine mains wiring method in 99% of the work we see around here, allowed basically everywhere NM can be used. This is spelled out in NEC 362.10, with point 1 applying to us:

(1) In any building not exceeding three floors above grade as follows:

a. For exposed work, where not prohibited by 362.12

b. Concealed within walls, floors, and ceilings

Note that ENT uses PVC fittings and conduit bodies, by and large, although special "snap lock" fittings can be used for ENT if cementing is undesirable for some reason. This also makes it easy to transition to PVC for the outdoor section of the run, as well.

Fill wise: you're good to go, but not by much

Your 4 4AWG THWN wires take up 212.64mm² of fill, while your 1" ENT has 215mm² of usable space, making your proposed pull quite a tight fit. I would downsize the ground wire to 8AWG if I were in your shoes; that's the minimum size required by the NEC for all circuits up to 100A, and will save you 29.55mm² of fill.

Garage panel selection and grounding

Since this is a feeder to a detached building, we know we will need to put a subpanel in at the garage. Furthermore, this subpanel will need to be a main breaker type, as that's the cheapest way to provide a local shutoff means at the garage, and have separate ground bars fitted so that neutral and ground are separated properly at the subpanel. Finally, we'll want it to be of ample size so that you don't need to go back and replace it later because it filled up: a 24- or 30-space, 100A or 125A panel will do the trick here, and isn't much costlier than a smaller panel would be. Don't forget to ensure the bonding screw or strap is pulled when the panel is installed!

Since this is a detached building, we also need to make sure that the garage has a proper grounding electrode system fitted. At its simplest, we can use two 8' deep ground rods, driven 8' apart, and connected to each other and to the garage subpanel's ground bar with 8AWG copper wire to handle that in this case.

TORQUE ALL LUGS TO SPEC

When fitting the new wires and panel, you will need to use an inch-pound torque screwdriver or torque wrench to torque all breaker and panel lugs to the torques printed on the labeling. This is required by 110.14(D) in the 2017 NEC, and also a good idea even if your AHJ doesn't require it, lest your electrical system lose you the race!