Electrical – Caulking/Sealant for Conduit Pipe on Roof

caulkingelectricalexteriorhvacroof

I had a contractor come by my house recently to do AC maintenance for the unit located on my roof. While up there, he mentioned that the conduit pipes that carry the electrical wires were not rated for exterior use and could create problems at the joints. A solution he proposed was to take some silicone caulking and just cover the joints to help prevent water from getting into the pipe.

Does it matter what type of caulking I get, should I just look for a product that is 100% silicon and call it a day, or is there another type of sealant that I should look for?

I would prefer not to have to replace the conduit piping since there is a lot up there (there are 5 other units in my building) and prefer a DIY solution that will help mitigate any problems until ALL of the conduit on the roof can be replaced.

Here are pictures of the joints I am talking about: http://imgur.com/a/xYhhR

Best Answer

From the Steel Tube Institute (an institute comprised of various steel conduit manufacturers):

Question: Can EMT be used on roof-tops?

Answer: There is no prohibition in the NEC. In some installations, there may be a concern about physical damage or corrosion protection. This is often a judgment call by the authority having jurisdiction. The NEC does not allow EMT to be used where, “during installation or afterward, it will be subject to severe physical damage.” The NEC also requires the EMT to be “securely fastened in place” and provides requirements for supports. The AHJ may determine more supports are necessary. If the AHJ approves the installation with EMT, consideration should be given to compliance with NEC 110.12, 300.6, 300.7(A) & (B), 358.10 and 358.30.

So, if your conduit was installed with fittings designed for a "wet location" (it looks like those are, but confirm) and it is properly supported, and provisions for expansion were provided (if required), then you should be OK. Most importantly, if the Authority Having Jurisdiction (AHJ) approved the installation, then you are fine.

In the end, it would not hurt to apply silicone. Use 100% silicone and clean the area(s) first so it sticks.

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