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#12684 08/14/02 08:31 PM
Joined: Aug 2002
Posts: 5
ant540 Offline OP
Junior Member
I was wondering what the NEC says about installing UF cable exposed, under a deck that is not easily acessible. Any help would greatly be appreciated.

#12685 08/14/02 08:55 PM
Joined: Apr 2002
Posts: 914
If you read article 300.4 I beleive you would be fine with UF under the deck. #1 the UF is rated for exposure and #2 the deck with limited access affords the required protection. Even if the deck was exposed under, as long as the wire is bored through the joist or stapled to the side of the joist, you meet 300.4. This is my opinion and if I'm wrong someone will correct me.

#12686 08/15/02 01:39 AM
Joined: Mar 2002
Posts: 95
We always install underdeck wiring in PVC with THHN, it'll be there if you ever go back.

Lighting the way
#12687 08/17/02 06:16 AM
Joined: Jan 2002
Posts: 1,457
joeh, why would the uf not be there also? I beleive this is perfectly acceptable and MUCH esier than installing pvc.

#12688 08/17/02 07:59 AM
Joined: Jul 2001
Posts: 311
I cannot find a Code restriction prohibiting the use of UF cable in this application.

#12689 08/17/02 08:55 AM
Joined: Oct 2000
Posts: 2,749
The UF cable must be marked as "UF-B cable."

THHN is not allowed in a wet location, and the comment made here indicating that PVC was used with THHN may be considered as a violation, especially when subject to flooding conditions.

If the location was considered as a damp location then, THHN may be OK, see Table 310.13.

Sometimes rodents like to chew on the insulation and that can lead to problems.

If I was doing this job, I would avoid stapleing the cable under the joists and would try to keep it concealed, if possible.

This, as always, is my personal opinion.

Joe Tedesco, NEC Consultant
#12690 08/17/02 10:01 AM
Joined: Nov 2000
Posts: 2,236
Likes: 1
Joe, you're right as usual, however, I'm sure the other joe meant the dual rated THHN THWN, 'cuz I've seen no THHN that isn't rated THWN, and calling it the wrong thing doesn't make it lose its wet rating, correct?

The stuff I use says the following, maybe y'all use different stuff.


Could we just call it THHN and assume we're all talking about the same thing?

BTW, if I ask my supplier for THWN, they usually say "We don't carry that, but we can order it", then I'll say "Oh, just give me THHN instead."

I get exactly what I wanted in the first place!

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#12691 08/17/02 12:29 PM
Joined: Oct 2000
Posts: 2,749

"THHN" is "THHN" and when we use words here, or terms that are read by some who are not as familiar with our trade we should be exact.

Sure, I knew what was meant, but still feel we should all strive to be very accurate, in fact look at what I found here:

I found an installation that used straight THHN in an underground run last year in a brand new installation!

Look here for UL Marking Guide Information:

[This message has been edited by Joe Tedesco (edited 08-17-2002).]

Joe Tedesco, NEC Consultant
#12692 08/17/02 03:14 PM
Joined: Mar 2002
Posts: 95
Yes I should have clarified THHN/THWN. i've always seen it marked together. It would be at the installers discrection to determine damp or wet location and then provide the right materials for the job.
I must say that most deck wiring that I've done lately would be visible from below. A house on a hill with a ground floor entrance and a second floor deck, hence my willingness to use PVC. My thoughts of UF and standard steel staples, that might one day rust out and allow the cable to fall away from the structure was my reason to use PVC, two hole straps and stainless steel screws. Alot of my work comes from referrals and to have a potental customer see a professional job several years down the road, would encourage me to go the extra mile so to speak and bid the job as I have done.
In a ground level deck situation where traffic disturbing the wire may not be an issue, and economy is a concern the UF if attached with the two hole plastic straps and stainless screws should do fine.
Sometimes a code installation may be acheived through several avenues, mine may seem overkill to most but short of RMC I feel comfortable with it.

Lighting the way

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