I am installing an ev car charger in my attached garage and running pvc conduit from my main panel in the basement through the wall into the garage. What is the recommendation for using duct seal inside the conduit where it enters the car charger, conduit body, or main electrical panel since none of the conduit is located on the exterior of the house, but is in an attached garage?

Also, is there a concern when applying duct seal inside conduit that by surrounding/touching the thhn and blocking the conduit lumen it can affect conduit fill or result in increased heat build up?

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    I've never heard of putting duct seal inside a conduit, just around the outside to keep stuff out if the conduit is in a large hole in the wall. Why would you need it inside conduit? Nov 21, 2023 at 18:51

1 Answer 1


There are a number of situations in which sealing of electrical and communications conduits may be required. These are usually focused on preventing liquids or gases from transiting through the conduit. An infographic from manufacturer Polywater details some of these.

It seems to me that conduit seal is likely not required in your circumstance, but it may still be somewhat beneficial. If nothing else it'll help prevent insects and cold air from entering the house.

No, duct seal doesn't factor in to conduit fill or heating. Conduit sizing and fill normally do not consider convective cooling (air circulation through the conduit) so blocking the air flow is not a problem.

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