Stripping UF-B for conduit use? [duplicate]

Question

Just a quick question,I've asked around, and have had conflicting answers.

Basically, can you strip UF-B (12/2) into its individual wires and run it through PVC conduit. I was planning on just running the 12/2 through the conduit ( i would be using 3/4 "),, but if it was allowed to strip that UF-B down i would be able to use 1/2 conduit?

The local electrical store assured me that running the 12/2 UF-B through 1/2" conduit is acceptable, but i understood that it had to be a certain size on conjunction to the wire size.

Answer 1

People often toss out the word "conduit" without really saying what they are doing with the conduit.

Conduit being fully run, end-to-end as a wiring method

Then you must follow all the conduit rules. The conduit must begin and end in a junction box. Thermal derate (no more than four 15-20A circuits in a pipe) must be respected. Physical fill rules must be respected, which almost precludes the use of UF cable, as it is very wide for its size, and thus requires a huge conduit (e.g. 2" for #6 conduit).

For a single cable, a shortcut is that the minimum pipe size ID is 138% of the maximum cable width.

The conduit must be fully built, glued, filled and tamped before any wires are PULLED into it. That means the conduit must be built to be pullable - with broad sweeps at inaccessible curves, and "pulling points" where feasible.

Cable in conduit is generally considered a nightmare, and very difficult to pull.

However this is not the same thing as

A stick of random pipe merely as a damage shield in one location

Sometimes when you are running NM, UF or SE cable, you have a short distance where the cable needs an additional bit of protection from physical damage. E.G. because you cannot run inside a wall, must run on the surface of the wall, such as coming down the wall on a poured concrete basement wall.

You can use any bit of random metal for this protection (that is tough enough), including pipe, including pipe that is made to be conduit.

However, at that point you are not using it as "the conduit wiring method", you are using it only as a "random piece of metal" to provide additional damage protection.

In this case, the "conduit as a wiring method" rules do not apply. Pipe fill is not a concern - if it fits, it ships. You can slide the pipe over the cable as you go. The cable can exit the pipe without a junction box. It doesn't need to be electrical conduit types specifically - heck, it doesn't even need to be pipe.

It does need to meet certain standards for physical protection, and cheapo PVC pipe or conduit typically doesn't - it's too easily broken.

Since copper pipe is expensive and some PVC is insufficient, EMT metal tubing is often used.

And if you want to extend the EMT into one junction box and put a receptacle there, that is fine.

Answer 2

You cannot strip cable and use it in conduit, as the individual wires in the cable are not marked.

If someone made cable with the wires marked, you could do that, but nobody does, AFAIK.

One example of 12/2 UF I found claims the major diameter is 0.463 inches. For a single cable in conduit you treat that as a round wire of that diameter, and use the one-wire fill percentage of 53% of the area. The back of my envelope says 1/2" PVC (0.578" ID Schedule 40, smaller for Schedule 80) won't meet that spec. Even 1/2" EMT (0.622" ID) is not quite big enough.

3/4" PVC even at Schedule 80 (which is often needed, because it's required if the conduit is considered "exposed to damage") should work with an ID of 0.698" (which my envelope puts at ~44% fill.)