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I am doing a very short run of a 2 inch PVC conduit on an external, west-facing, brick wall. The conduit exits the panel horizontally, travels 28 inches, turns 90 degrees south and travels 36 inches where it terminates into a conduit body which then enters into the crawl space of the house.

The seasonal temperature fluctuations in my region have a range of about 100F. Also, because the conduit will get direct sunlight, add another 30F for a total of 130F. Based on this, I do need expansion couplings.

According to this Carlon EC infosheet, at 130F, you can expect a PVC expansion of 5.3 inches over 100 feet. For my run of ~6ft, this expansion comes out to 0.318 inches.

As per NEC, ECs are required if the expansion is expected to be above 0.25 inches. So I am just barely above this limit. Furthermore, it seems people generally only use ECs if the run is longer than 25ft between two secured points. My run is much shorter than that.

Do I need to use an expansion coupling? The problem is that there is no space for an EC to fit in either of the two short runs (vertical and horizontal). Do I really need to make my run longer just so I could fit in an EC?

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  • How about using flexible conduit ?
    – Traveler
    Jun 10, 2022 at 3:20
  • Are you taking into account UV deterioration of the PVC as well?
    – Reid
    Jun 10, 2022 at 15:34
  • @Reid I am using SCH80 PVC. What else can anyone do other than not using PVC at all.
    – cryptic0
    Jun 10, 2022 at 16:29
  • What is so awful about metal conduit? And, I want to make sure, the corner is a large-radius sweep, right, not a literal elbow? Jun 10, 2022 at 18:57
  • I already crossed that bridge. My entire run is pvc. If it fails in 20 years, the next homeowner can replace it with metal conduit. I don’t feel like throwing away $300 worth of pipe and fittings now.
    – cryptic0
    Jun 10, 2022 at 19:05

3 Answers 3

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Practically speaking, for purposes of expansion, you don't have a 64 inch run. You have a 36 inch run and a 28 inch run, and the 90 degree corner between them means the motion of one will not be adding to the motion of the other. So your actual expansion movement is roughly half what you calculated.

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  • Thanks. I was just about to update my question with something similar. In addition, I have a 90 elbow, a meter offset and a conduit body which will further reduce the length of my run. So I guess that resolves the issue then. I do have a much longer run in the crawlspace where I plan on installing the ECs I purchased earlier.
    – cryptic0
    Jun 10, 2022 at 3:25
  • @cryptic0 when you say "90 elbow", you mean a large-radius sweep, right? Jun 10, 2022 at 19:01
  • Yes, large radius with bell end on one side.
    – cryptic0
    Jun 10, 2022 at 19:03
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My first take on that is "use metal conduit".

I don't quite understand why metal is so disliked. It does a number of things much better:

  • No gluing, so easy to rework if mistakes are made, you risk nothing but pipe.
  • Does not burn or make toxic smoke (a handy property in a thing carrying wires). PVC is literally made of petroleum.
  • carries the grounding path for you, so no ground wire needed
  • a damaged wire will ground to the conduit and trip the breaker successfully
  • let it age a year and it will take paint quite well
  • and, better thermal expansion

The only thing I can think is that some people already have the craft of working with PVC drain pipe so this feels more in their comfort zone. Really, EMT is not that hard, and it's fine since you're not going underground.

If you want to run PVC pipe elsewhere and are worried about a transition, it's easily done at a "threaded" connection. Just use a threaded male connector on the EMT (like you'd use to enter a box, leave off the nut) and a threaded female glue-on connector for the PVC. Or a threaded male and a threaded coupler, sold in either metal or plastic.

Second take: don't glue the sweep

You can't use elbows in conduit, you need to be able to pull the wire through. Because you're not allowed to assemble the conduit around the wires.

Therefore, your "corner" must actually be a broad sweep. That sweep on a 2" (50mm) pipe will be eating up much of your 28" (700mm) and 36" (900mm) run. That's why you don't have room for an expansion joint.

enter image description here

An example of a sweep.

Anyway, my second thought is, PVC pipe joins happen via the end of the pipe being flared out to match the outside diameter of the pipe (as shown). This sleeves over the next pipe. So hey. Free, poor man's expansion joint - just don't glue it.

This would be a Code violation technically, so you'd have to throw yourself at the mercy of the AHJ to get it approved. You're not supposed to use that for an expansion joint because there is 3-ish inches (80-ish mm) of overlap, and on a long straight run, the expansion would tend to happen all at one joint and it would pull apart. But you have maybe 3/16" (5mm) of travel in each dimension, so it shouldn't be a problem. Just make sure to assemble them 3/8" (10mm) shy of bottomed out.

But with those joints floating, there is no structural strength there. So you need to severely anchor the straight pipes to the wall, as those anchors will have to bear ALL force of lawnmower hits and the like.

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  • Thanks for taking the time to elaborate on the topic. As you correctly surmised, my main issue with EMT is how to transition it to PVC. If I were to replace the external piping with EMT, I will need two 90 degree turns. For the first turn, I could use a large sweep elbow (but without threads how to join them?). For the second turn, I must use a conduit body. How can I transition to a PVC conduit body from EMT? Finally, I also need a meter offset, but don't see one listed for EMT.
    – cryptic0
    Jun 10, 2022 at 20:38
  • Where are you looking? EMT uses setscrew or compression couplers. I honestly didn't know PVC offsets existed, I thought they only existed in RMC, that's what you use plus a female-female threaded coupler plus an EMT connector. At the LB conduit body, either use a made-for-EMT conduit body, or a threaded conduit body (RMC or plastic) and EMT connectors. Getting from PVC glued to threaded is super easy, in fact when I do PVC (not often) I use threaded entries into boxes not glued. Jun 11, 2022 at 1:14
  • How would you keep threaded connections you mention above rain tight?
    – cryptic0
    Jun 11, 2022 at 1:36
  • There is no such thing as "rain tight" in conduit. No conduit system is capable of that, not even "raintight", and we must plan accordingly by choosing outdoor rated wires. But some teflon wouldn't hurt. Jun 11, 2022 at 1:54
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They make mini-me expansion joints for this

As it turns out, Carlon makes shorter versions of the normal expansion fittings for space-constrained apps like yours. Your 2" application uses an E955J, to be precise -- it's less than 5" long.

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