Romex outdoors?


Old 01-18-05, 09:13 AM
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Join Date: Jan 2005
Location: United States
Posts: 455
Romex outdoors?

Can I use exposed romex outdoors? Specifically under a deck attached to the joists?

If so, how far above the ground does it have to be?

What is the rule for when it has to be enclosed in NM conduit?
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Old 01-18-05, 09:27 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
There are no codes which prohibit NM "outdoors". And there are no codes about how far off the ground it must be.

However, code does require it to be in a "dry" location. It also requires it to be "protected from physical damage." If the area under the deck is used for living or storage or even walking through, it will likely need more protection than offered by stapling it to the bottom of the joists in a perpendicular run (although stapled to the side of the joist in a parallel run is okay). Also note that NM is not sunlight resistant, so it needs to be protected from exposure to the sun.

If you're not very certain that the area is not subject to excessive moisture or dampness, I suggest you run UF instead. UF is available is sunlight-resistant cable as well.

The code is not very clear about when NM is allowed to be in conduit. It is clearly allowed for short (no definition of "short") runs when used for protection from physical damage (like under a deck). But exactly when it is allowed or disallowed is a subject of much debate.

Note that conduit does provide protection from physical damage, but it doesn't really provide any protection from dampness. The inside of conduit can be a very damp place even if you think you sealed it well.

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