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#97734 - 03/19/06 01:32 PM Protecting NMD90 (loomex) after construction
montreal Offline
Member

Registered: 03/19/06
Posts: 10
Loc: montreal,quebec,canada
Protector plates are prescribed whenever it is impossible to guarantee a minimum distance (typically 2 inches) between the outer surface of the half inch gypsum wallboard and the loomex wire passing through holes in the studs.

These protector plates appear to be uniquely marketed as a product that protects wiring during the construction phase.

My question is about the obligation to protect wiring during the post-construction phase, during the many decades of time when the wiring is vulnerable to the naivety of the homeowner handy-person.

Specifically, the homeowner may wish to insert screws or nails of significant length into the wall or ceiling in order to attach decorative objects. Where many electrical wires converge enroute to a distribution panel, the risk of puncturing a cable increases whenever the critical length of metal fasteners is exceeded and the hole location is close to the area of concentration.

In a recent installation of recessed lighting, I was obliged to concentrate 14 loomex wires in the ceiling of a family room. Where the wires converge, the distance from the outer surface of the wallboard to the wires is only 1 inch instead of the usual 2 inches.

Because no wallboard screws or nails were needed in the area of the concentrated wiring, I did not use protection plates to compensate for the reduced clearance of 1 inch. There was never a danger of these wires being damaged as the ceiling was being closed up.

However, I am now concerned about the potential danger should a future owner of this home decide to insert fasteners in the ceiling with no regard to the location of the wiring.

I now have the option of opening up part of the ceiling and inserting a 1 foot by 10 ft heavy steel sheet to provide the same degree of protection afforded by a typical commercial protector plate for wood studs.

Or I could simply provide a blueprint that details the position of the wires that have reduced clearance. But over decades, blueprints can be lost or forgotten about.

So I am asking where should one draw the line in deciding how much protection is reasonable in a world where people blindly procede?

Thanks

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#97735 - 03/19/06 04:54 PM Re: Protecting NMD90 (loomex) after construction
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I am not sure about Canada but the US NEC is woefully inadequate in protecting non-metalic cables.
They worry about the drywall guy who knows where the studs are but the homeowner is on his own
_________________________
Greg Fretwell

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#97736 - 03/20/06 07:10 AM Re: Protecting NMD90 (loomex) after construction
montreal Offline
Member

Registered: 03/19/06
Posts: 10
Loc: montreal,quebec,canada
Thanks for your response.

After my initial post, I came across another thread in this forum that deals in part with the same subject:
http://electrical-contractor.net/ubb/Forum2/HTML/000981.html


As you say, the code spells out the minimum that is required to protect the wiring from the 1-5/8" screws of the drywall installer.

Para 300.4(D) also proposes that cable runs parallel to framing members be kept a minimum of 1-1/4 inches away. I believe that this is as much for the benefit of homeowner (attaching a heavy shelf), as it would be for the benefit of a kitchen cabinet installer.

In the case of the homeowner installing a heavy shelf, the homeowner could be expected to use a nail or screw which exceeds the typical length of a 1-5/8 inch drywall screw and seek out a stud to accept it.

The code seems to allow the homeowner a safety zone of 1 1/4 inches on either side of the stud in case he/she accidentially misses the stud.

Another paragraph I came across says:

"Also NOTE - Nonmetallic-Sheathed Cable and Electrical Nonmetallic Tubing. Where nails or screws are likely to penetrate nonmetallic-sheathed cable or electrical nonmetallic tubing, a steel sleeve, steel plate, or steel clip not less than 1.6 mm (1⁄16 in.) in thickness shall be used to protect the cable or tubing. "

This leaves the decision up to the electrician to imagine what folly the future homeowner(s) might create. This suggests that if 1) cable runs converge in walls or ceilings as they approach a distribution box, and if 2) these cables pass through holes in framing members, and even if 3) the holes are set in at least 2 inches from the outer surface of the drywall, and if 4) the electrician believes that a future home homeowner would likely want to install a heavy shelf in such a location, then the electrician has the responsibility to provide aditional protection with 1/16" thick steel plates.

For what its worth, I tried drilling a 1/8 inch diameter hole in such a steel plate and it takes very little extra force compared to drilling through wood and about an extra 10 seconds to pierce the steel plate.

These steel plates work perfectly in preventing a drywall screw from contacting the wire, but it would take a stainless steel plate to adequately discourage a naive homeowner in his or her attempt to drill into a dangerous wiring zone.


Thanks again for posting.

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#97737 - 03/20/06 09:44 AM Re: Protecting NMD90 (loomex) after construction
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
The real issue here is in an exterior masonry wall that is only furred out 3/4". Florida used to require that these cables were in EMT where they are trapped against the block. Now if they run 1.25" laterally from the furring strip they are OK. Horizontal runs do not require any protection once they are 1.25" from the furring. If you have a homeowner hanging pictures it is very easy to see them piercing a wire with nothing but an angled pin picture hook.
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#97738 - 03/20/06 12:34 PM Re: Protecting NMD90 (loomex) after construction
montreal Offline
Member

Registered: 03/19/06
Posts: 10
Loc: montreal,quebec,canada
Protection plates are 1/16" by code and are easy to drill through. If you felt it necessary to include your own custom designed protection plates in order to protect vulnerable cables from a homeowner's 1/8" diameter drill bit, what thickness of steel plate would you choose in order to slow down the drilling enough to discourage the homeowner from continuing?

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#97739 - 03/20/06 04:50 PM Re: Protecting NMD90 (loomex) after construction
hbiss Offline
Member

Registered: 12/16/03
Posts: 893
Loc: Hawthorne, NY USA
I made that same argument. The code requires 1-1/4" from the face of the stud or a nail plate. Nothing is required in the middle of the bay and the cable can contact the back of the sheetrock.

a 1 foot by 10 ft heavy steel sheet...

Funny you should say that. I did exactly that once for two bays in a finished ceiling where I had run many home runs back to the panels. I didn't like the way some would rest on the sheetrock.

I had a friend who worked for the railroad as an electrician. He had access to stainless steel sheet that they used to repair the skin on the cars. You ain't gonna put a screw through that stuff!

-Hal
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#97740 - 03/20/06 07:47 PM Re: Protecting NMD90 (loomex) after construction
montreal Offline
Member

Registered: 03/19/06
Posts: 10
Loc: montreal,quebec,canada
Today, I visited my city inspector who has worked with metal as a hobby and we debated the advantages of using stainless steel instead of rolled steel.

We both agreed that a drill bit can go through stainless but we disagreed about the difficulty of doing so in each of the two types of steel.

In the end, he encouraged me to choose rolled steel of at least 1/8" thick (twice code) instead of 1/16" of the much more expensive stainless.

My last question to him was - what does it take to convince a foolish person to abandon drilling?

My inspector suggested that I should concentrate on providing a level of security that any insurance company would consider adequate (retrofitting a large metal plate) rather than worry about the imprudent homeowner who would have just as many chances of drilling through any of the dozens of other cables buried in studs scattered all over the house.

Hal, thanks for suggesting the stainless steel and do you remember how thin your friend's sheet really was?

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#97741 - 03/20/06 08:41 PM Re: Protecting NMD90 (loomex) after construction
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Blue spring steel would stop them. That stuff is harder than a hacksaw blade. There are different grades of stainless. Some are not that hard.
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Greg Fretwell

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#97742 - 03/21/06 06:15 AM Re: Protecting NMD90 (loomex) after construction
montreal Offline
Member

Registered: 03/19/06
Posts: 10
Loc: montreal,quebec,canada
If blue spring steel is harder to drill through than stainless, in order to discourage a homeowner while drilling, what is the thinnest stock that would be adequate and can a typical sheet metal shop cut the sheets with their shears or do they need to use a torch to cut it?

We are talking about covering an area of about 1 foot by 15 feet.

Thanks

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#97743 - 03/21/06 09:09 AM Re: Protecting NMD90 (loomex) after construction
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I think you are at the mercy of the code (1/16") and I doubt they even make spring steel that thick but I tried to fab up a replacement for a wierd size recess can ring retainer spring and destroyed a couple DeWalt drills getting a mounting hole in the spring stock I had in my junk box. I think they must cut and drill this stuff before they harden it.
I agree the mild steel in kickplates would be a minor inconvenience to a determnined homeowner. I know you can shoot a fine thread drywall screw through it too if you had a little patience. The rockers know what it is supposed to feel like so they should not be doing that but my favorite builder had a flood because a rock screw went through a plumbers kickplate and a pipe. It took a while to start leaking and longer to find.
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Greg Fretwell

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