Conduit questions

[paul32]

Under what conditions, like how long a run and wire size being pulled, do you have to do the following:
1. Use larger than code minimum conduit
2. Need to use a metal elbow in a PVC run
3. Need to use wire lubricant
4. Not pull by hand

A really short run you could push the wires through, at some length fish tape is needed, at a longer length lubricant is needed. I'd like some general rules to follow, or if there is a good reference I should go to that would be great.

I'm planning an underground run of 1/2" PVC sch 80 for a detached garage (3 14AWG THWN conductors). It is about 42 feet between elbows, which both go up to LBs. My gut feeling says this will not need lubricant or metal elbows and can be pulled by hand.

Is anything special needed to protect the conduit from ground movement due to frost, since it is not below the frost line? Expansion fittings on the two vertical parts?

Thanks in advance. I haven't said so before, but this form is great and has been a great help.

 

[bphgravity]

Re: Conduit questions

Questions 1-4 are not within the scope of the code and are "learned" through experience and training. The code has written in rules to help with these issues such as conduit fill restictions and by limiting the number of bends between runs of a raceway. Everything else will have to be a judgment call based on all factors, like how strong the puller is or how hot it is that day. There are too many factors to consider.

A metal elbow is generally not needed for hand pulls. When you use a mechanical puller, the constant "tug" along the elbow can and will cause damage to both the conductors and the fitting.

Section 300.5(J) covers the requirements for ground movement from the settlement of frost.

 

[jimwalker]

Re: Conduit questions

Why shedule 80 ? and do yourself and the next guy a favor and use at least 3/4.That is a very min circuit that someday might not be enough.Metal elbows are not needed or lube

 

[iwire]

Re: Conduit questions

You are asking for opinions so I will offer a couple.

Forget about 1/2" PVC sch 80 conduit, the inside diameter of this is very small, much smaller than 1/2" EMT.

1/2" EMT internal diameter is .62"

1/2" PVC sch 80 internal diameter is 0.526"

That may not sound like much but it makes a difference.

If I was doing this job I would use 3/4" PVC minimum with at least 12 AWG THWN.

Truthfully I can't remember the last time I used less than 1" and 10 AWG underground.

I would fully expect to hand pull this dry and as bphgravity has said you can usually forget the metal elbows unless pulling with a machine.

 

[dave55]

Re: Conduit questions

I'll start out by confessing that I have absolutely no experience with PVC. I just wanted to bring to your attention a note after Article 300.5(B)Grounding (2002 Handbook).

"Rigid nonmetalic conduit elbows installed as part of a long run of conduit are often damaged in the process of pulling the conductors, due to the friction of the bend".

Dave