UF Cable Behind Stone

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
I know the code says UF can't be embedded in poured concrete but what about behind stone? The stone will have a mesh wire backing and mortar behind & between the stones,
 

oldsparky52

Senior Member
I know the code says UF can't be embedded in poured concrete but what about behind stone? The stone will have a mesh wire backing and mortar behind & between the stones,
Where are you wanting to install the cable? You said the stone will have mortar behind & between the stone and you also asked about installing it behind the stone. Would that be behind the stone in the mortar or below the mortar?
 

GoldDigger

Moderator
Staff member
Just for a moment, looking at the phrase "embedded in poured concrete", I wonder if the poured part was really intended to be significant?
If you have precast concrete (like a slab) and the UF is underneath it, you do not have poured concrete but the wire will also certainly not be embedded in it.
On the other hand, you could embed a wire or cable in sprayed concrete, like gunite or shotcrete. Would that really be OK?
 

Beaches EE

Member
Location
NE Florida
Occupation
Electrical Engineer / Facilities Manager
The code says "in poured cement except as permitted in 424.43" and that section deals with non-heating leads of heating cables. Mortar is not poured concrete so embedding the cable in the mortar behind the stone seems to be permitted.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Where are you wanting to install the cable? You said the stone will have mortar behind & between the stone and you also asked about installing it behind the stone. Would that be behind the stone in the mortar or below the mortar?
It would go on an outside wall. There is a mesh screen that goes on to help hold the mortar, then some mortar, then the stone with mortar between the stone. The UF would go over the mesh before any mortar is applied.
 

wwhitney

Senior Member
Location
Berkeley, CA
(2015) 340.12(8) prohibits UF "Embedded in poured cement, concrete, or aggregate". To me that prohibits the proposed installation.

I take the word "poured" there to mean "cast in place", versus running through a chase in a precast member, e.g. a concrete block. And mortar is just concrete without the coarse aggregate, more or less. The proposed installation is definitely embedded in a cast-in-place cementitious material.

Now if you have the thickness to cover the the UF with a barrier before applying the mortar, then I would say it is not embedded, and you'd be fine.

Cheers, Wayne
 

kwired

Electron manager
Location
NE Nebraska
The code says "in poured cement except as permitted in 424.43" and that section deals with non-heating leads of heating cables. Mortar is not poured concrete so embedding the cable in the mortar behind the stone seems to be permitted.
That section applies to heating cables as well as the non heating leads as you mention but not to UF or other general wiring methods.
 

kwired

Electron manager
Location
NE Nebraska
(2015) 340.12(8) prohibits UF "Embedded in poured cement, concrete, or aggregate". To me that prohibits the proposed installation.

I take the word "poured" there to mean "cast in place", versus running through a chase in a precast member, e.g. a concrete block. And mortar is just concrete without the coarse aggregate, more or less. The proposed installation is definitely embedded in a cast-in-place cementitious material.

Now if you have the thickness to cover the the UF with a barrier before applying the mortar, then I would say it is not embedded, and you'd be fine.

Cheers, Wayne
I also agree. Mortar is typically "cast in place". What is allowed is to drill a hole through the concrete, mortar, etc. after it is cured and then install the cable.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I'm not seeing how you can say that installing UF cable in a thin coat of mortar is the same as being "(8) Embedded in poured cement, concrete, or aggregate". Mortar is not poured cement, concrete, aggregate or plaster.
 

tkb

Senior Member
Location
MA
Mortar is applied, not cast in place.
Casting requires a mold, a mold for concrete is the forms that need to be removed after the casting.

There is no mold when applying mortar to masonry units.

Thus, UF in mortar is not a violation.
 

wwhitney

Senior Member
Location
Berkeley, CA
I'm going to continue to disagree, on the basis that the proposed installation is well within the boundaries of obviously prohibited installations. Suppose the wire mesh was stapled to a floor, not a wall, and was going to get covered with a thin layer of self leveling cement and then stone. That's obviously prohibited, but the result is basically identical to the proposed installation, just rotated 90 degrees and with even finer aggregate in the SLC than in mortar..

Seems to me it would be easy to separate the UF from the cementitious material so there would be no question. E.g. if behind the wire mesh is a plywood layer, just groove the plywood layer and put the UF in the groove. Or cable tie the UF to the wire mesh, and then cover it with a 1-1/2" plastic strip fastened tight to the mesh, so there's no embeddedment.

Cheers, Wayne
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I don't see how it matters that an install is similar to a prohibited install as long as it is not the prohibited install. The code does not say you can't do something similar to what is specified as prohibited.
 

wwhitney

Senior Member
Location
Berkeley, CA
Agreed, similar is not enough, you have to draw the line somewhere, and similar could be just over the line.

My statement was that it was within the boundaries (defined by) obviously prohibited installations. If Method A is prohibited, and Method B is prohibited, then Method (A+B)/2 (whatever that means) is prohibited.

As to more specific commentary, what is the point of this section? Is it just to prevent mechanical damage to the UF cable while the "cement, concrete, or aggregate" is placed? (Don't lay your UF down in between lifts of drain rock). Or is also there a concern about the UF cable embedded in a cementitious matrix? E.g. that stresses in the material could be transferred to the cable itself (the cable becomes an inadvertent reinforcing bar).

I've been assuming the latter is at least part of the issue, that the result matters, not just protecting the cable during installation of the other material(s). But if it is just about protection of the cable during construction, then the OP's proposed method should be OK.

Cheers, Wayne
 
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