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Joined: Nov 2007
Posts: 763
KJay Offline OP
I was just wondering about something I noticed while looking over 225 of the '08 NEC.

225.21 Multiconductor Cables on Exterior Surfaces of Buildings.
Supports for multiconductor cables on exterior surfaces of buildings shall be as provided in 230.51.

230.51 references,
[A] Service Cables...
[B] Other Cables... not approved for mounting in direct contact with a building...
[C] Individual Open Conductors ... shall be installed in accordance with Table 230.51[C]...

What does this mean if for some reason you need to install 14/3 UF branch circuit wiring on the exterior of a building?
Is it required to be supported as SE cable? Meaning within 12-inches from a raceway or enclosure and then at interval of not more than 30-inches.

Art. 340 doesn't seem to reference support of UF cables other than by cable tray or unless it is being installed as NM cable.
Would using UF outside a building qualify as installing it as NM cable? Since NM wouldn’t be allowed outside.

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Joined: Jul 2004
Posts: 9,696
Likes: 11
I would say the 08 code says this was a cable installed on the outside surface of a building and it should be supported 12" from the box and 30" along the run. Wind load alone would make this a minimum requirement IMHO.
If anything the 14-2 UF would be more at risk of flapping around than SE.

Greg Fretwell
Joined: Nov 2007
Posts: 763
KJay Offline OP
That's what it sounds like to me as well. I have to admit though, I've never really given 225.21 and using UF cable much thought together, since normally the only cables I attach to outside of buildings are usually SE/SER, coax and/or telephone, but it's good to know anyway, should the need ever arise.

This also gets me wondering if standard steel #12 or #15 staples like we use for NM cables in dry locations are actually listed or otherwise designed for use outside to secure UF cables to buildings. I've seen them used for this, but they always seem to be rusting quite badly.
I know that my local supply house now carries stainless steel #15 staples, which I assume would be designed for indoor/outdoor use, but not sure about this.

Joined: Jul 2004
Posts: 9,696
Likes: 11
Strapping outside is always a problem. The white nylon straps with 2 nails won't hold up to the sun, regular steel will be bleeding rust in a month around here, galvanized will buy you a few years but it will still be showing pinhole rust after a while. PVC is corrosion resistant but the UV protection of the straps seems to be weak to non-existent. I actually had a Carlon rep tell me the listing standard did not require U/V protection on straps and covers so they didn't do it. That may have changed since then (6 - 8 years ago).
I always had a lot of tolerance for improvisation in the strapping methods if they seemed secure and more weather tolerant than the products we have in the marketplace.

Greg Fretwell
Joined: Apr 2002
Posts: 7,299
Likes: 6
I seem to remember there was/is 'straps' for flat cable (UF/NMC) that were around years back. Possibly cad plated.

The rust situation was something that was not considered by the installer back then. And, UV degradation was a term that was non-existant.


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