NM Within Walls

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renosteinke

Senior Member
Location
NE Arkansas
Recently the question was asked: must all NM be run 1-1/2" back from the face of the wall, or is the requirement only for where it contacts a framing member?

I believe the case was made that the NEC only requires the set-back, or nailplate protection, at the framing members. I took this opportunity to visit one active jobsite, where the wiring illustrates this interpretation rather well.

First, here's a picture of the opened wall:

OpenWallEdit1.jpg


Demolition is in progress. Please note the paneling applied atop the 1/2" drywall. This is 2x4 frame construction, with the stud bays stuffed with mineral wool insulation. Now, let's look closer at the wiring method:

NMCrossingEdit.jpg


The wiring is run atop the insulation, just under the drywall. Looking to the studs, it does appear that they attempted to set their holes back:

NM2Edit.jpg


Also within this wall is the unfused cable from the outside meter pan to the panel on the opposite side of the room. That is, about 20ft. of cable is run up the wall, across the ceiling, and down another wall to the panel. There is NO way to kill power to this cable without calling the PoCo.:

SVC2Edit.jpg


Now, the 'eagle eyed' amongst us might notice that this cable is not quite perfectly parallel to the stud - it's not attached to the stud for support - so one might argue that the 'parallel' requirement would not apply.

Finally, to make sure everyone feels all warm and fuzzy, here's the backside of one piece of paneling:

Panelnailsedit.jpg


Please note that not every nail is lined up with the studs, and that the nails are plenty long enough to hit a wire; just wait until Granny hangs a picture from that service feed.

Personally, I think NM ought to be set back from the wall as much as possible; I recognize that the last inch or so where it enters a box is within the 'set-back' distance; there's not much we can do about that.

What say you of this installation? Allowed, or not? Would you sign off on it? If yes, do you see a need to alter the code?
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
Technically, I think the setback only applies to the hole or a framing member. Where the wire spans the space between studs, it is free to move if poked with a nail. Back in the days of hammering, the nail probably wouldn't penetrate since the wire would just move with the nail. With the nail guns they use today, they zip in so fast that they can penetrate a wire.

I think half the problem is awareness by other trades of the 1.5" code mandated clearance. They should not use nails that will penetrate beyond this, and in fact should use one even shorter since the wire may be closer between the studs or someone could have been a little off drilling the hole. Paying attention to exactly where the studs are helps too, as structural nails missing a stud will be likely to hit a wire.

I had my siding redone and was apalled when I saw the garage (the only place with no inside finish material). I saw nails poking through the sheathing by 1.5" (they were using 2.5" nails for a siding job). It was a miracle the no wires were hit. Just 6 months ago. I removed some drywall to redo wiring where the old service panel had been. One of those wires was punctured by a siding nail. Amazingly, it seems to have missed a conductor (this was old NM cable from the late 60's and the 14-3 was as thick as today's 10-3 and had fat kraft paper "twine" in it).

There are other things that are a pain with 2x4 walls (such as 2" and 3" plumbing). I'd like to see walls become 2x6 for the perimeter and interior walls with
2" and larger plumbing. I'd then still like to see wires run in the center, but they'll be about 2.5" from each stud face in this case. The deep plastic device boxes used today are also a problem on 2x4 walls. You can have wires less than half an inch from the drywall where they enter the back of the box. That's asking for trouble if someone decides to hang anything from the other side and fails to check for a box. So I'd mandate 2x6 walls...
 
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iwire

Moderator
Staff member
Location
Massachusetts
Well the unfused NM in the walls is an issue.

The NM between the insulation and the finish between the studs is not and any inspector failing it would be on shaky ground.
 

jusme123

Senior Member
Location
NY
Occupation
JW
Sec 300.4 clearly defines what is acceptable and what is not. For the most part, sec 300.4 states cable shall
1.25" away from outside edge of stud for protection of cable, whether it is run through or parallel with a stud.

The SEC would never pass NEC inspection as installed.
 

iwire

Moderator
Staff member
Location
Massachusetts
The pictures below illustrates how it is done here in my area every day.

Local codes require the strapping before drywall so we run our NMs in the void.

This is NEC compliant as far as being between the insulation and the drywall. These are just pics I found on the internet and appear to be DIY so there may be some issues with other aspects.

strapping2.gif



strapping1.gif


strapping3.gif
 
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renosteinke

Senior Member
Location
NE Arkansas
Then unfused service cable was taking advantage of another liberal interpretation of the NEC, regarding 'nearest the point of entry.' Up, over, and down to the panel on the other side of the room was 'nearest.'

Perhaps the wires can 'move' from a nail. I wouldn't want to rely upon that, and screws are another thing alltogether.

I have not seen strapping as Iwire pictures; I'm not sure what it's supposed to accomplish, but I can also see the temptation to run the wires there. I can't say that I like it. I've always run the wires dead center through the 2x4 studs, or stapled dead center along their sides. "Flying" the cable over the top edges of them is a new practice to my eyes.

Other than the exception of fishing a cable into a closed, insulated cavity, I've had the insulation guy work around the already-placed wires.

My favorite example of 'Murphy's law' was a siding contractor who ran a row of nails through the wall, into the 3/4" EMT that I had so carelessly placed (because of the bends) only 1" behind the face of the stud. Perfect aim: eight nails right into it! He completely missed the stud; Fortunately, I had not yet pulled the wires, let alone powered them up.
 

Strife

Senior Member
Recently the question was asked: must all NM be run 1-1/2" back from the face of the wall, or is the requirement only for where it contacts a framing member?

I believe the case was made that the NEC only requires the set-back, or nailplate protection, at the framing members. I took this opportunity to visit one active jobsite, where the wiring illustrates this interpretation rather well.

I want to quote my favorite:"You'll never be able to make something 100% idiot proof, someone will invent a better idiot". You mentioned grandma hanging some pictures, so what if grandma only has some 5" long nails? Shouldn't we consider that as well? You could drive a tank and still get killed in an accident. The ONLY WAY you won't get killed in an accident is to NEVER BE in a car. And even then you can have an 18 wheeler ram your house. So move 100 miles from ANY road, but even then.....
All we can do is reduce the risk, WE'LL NEVER be able to ELIMINATE IT.
Would you rather your house cost 100million dollars with 99.10% risk free, or would you rather it'd cost 100K with 99% risk free? How much you're willing to pay for that 1 millionth additional risk free?
The biggest problem I have noticed is oversized breakers. So I guess all wiring should be MINIMUM #3 for plug in breaker panels.
I had a few instances where the drywall guys managed to drive their screws through EMT conduit. Wouldn't that be a valid argument to have everything in rigid?
 
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acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
I want to quote my favorite:"You'll never be able to make something 100% idiot proof, someone will invent a better idiot". You mentioned grandma hanging some pictures, so what if grandma only has some 5" long nails? Shouldn't we consider that as well? You could drive a tank and still get killed in an accident. The ONLY WAY you won't get killed in an accident is to NEVER BE in a car. And even then you can have an 18 wheeler ram your house. So move 100 miles from ANY road, but even then.....
All we can do is reduce the risk, WE'LL NEVER be able to ELIMINATE IT.
Would you rather your house cost 100million dollars with 99.10% risk free, or would you rather it'd cost 100K with 99% risk free? How much you're willing to pay for that 1 millionth additional risk free?
The biggest problem I have noticed is oversized breakers. So I guess all wiring should be MINIMUM #3 for plug in breaker panels.
I had a few instances where the drywall guys managed to drive their screws through EMT conduit. Wouldn't that be a valid argument to have everything in rigid?[/QUOTE]

That won't stop the "bigger Idiot" from getting to it. I've seen guys hit a nail plate and grab a drill because something was stopping the screw from going in.
 

hurk27

Senior Member
Here is an image from the 2011 hand book with the rules allowed:
clip_image002.gif


should clear up any cornfusion.

And Bob your right in the first photo toward the back right the NM starts running right next to the furring strip need 1 1/4" not 1 1/2" 300.4(D)

Also remember the allowance of the fished between points rule as some of the OP photos looks like it? 334.30(B)(1)
 
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hurk27

Senior Member
I want to quote my favorite:"You'll never be able to make something 100% idiot proof, someone will invent a better idiot". You mentioned grandma hanging some pictures, so what if grandma only has some 5" long nails? Shouldn't we consider that as well? You could drive a tank and still get killed in an accident. The ONLY WAY you won't get killed in an accident is to NEVER BE in a car. And even then you can have an 18 wheeler ram your house. So move 100 miles from ANY road, but even then.....
All we can do is reduce the risk, WE'LL NEVER be able to ELIMINATE IT.
Would you rather your house cost 100million dollars with 99.10% risk free, or would you rather it'd cost 100K with 99% risk free? How much you're willing to pay for that 1 millionth additional risk free?
The biggest problem I have noticed is oversized breakers. So I guess all wiring should be MINIMUM #3 for plug in breaker panels.
I had a few instances where the drywall guys managed to drive their screws through EMT conduit. Wouldn't that be a valid argument to have everything in rigid?[/QUOTE]

That won't stop the "bigger Idiot" from getting to it. I've seen guys hit a nail plate and grab a drill because something was stopping the screw from going in.

well here we had a big problem with siders using 2.5" roofing nails so much for the 1.25" rule we even had them drive them right through the back of a 200 amp MB panel right through the buss (((KA-BOOM))) well after back charging for a new panel and labor they got the idea that we were not going to put up with there carelessness.
I mean how hard is it to relize that if you are installing siding in the area of the meter you need to check out where the panel is oh d'aaa!!
 
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iwire

Moderator
Staff member
Location
Massachusetts
And Bob your right in the first photo toward the back right the NM starts running right next to the furring strip need 1 1/4" not 1 1/2" 300.4(D)

Yeah I saw that ...

MA amendments

300.4(D). Delete this subsection.

:cool:


MA amendments

334.17. Revise to read as follows:
334.17 Through or Parallel to Framing Members and Furring Strips. Types NM, NMC, or NMS
cable shall comply with 300.4 where installed through studs, joists, rafters, and similar members.
Grommets or bushings shall be used in metal studs as required in 300.4(B)(1), shall remain in
place during the wall finishing process, shall cover the complete opening, and shall be listed for
the purpose of cable protection.
In both exposed and concealed locations, where the cable is installed parallel to framing
members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable shall
be secured so that the nearest outside surface of the cable is not less than 19 mm (? inch) from
the nearest edge of the framing member or furring strip
where nails or screws are likely to
penetrate. Where this distance cannot be maintained, the cable shall be protected from
penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm (1/16 inch)
thick. A listed and marked steel plate less than 1.6 mm (1/16 inch) thick that provides equal or
better protection against nail or screw penetration shall be permitted for this purpose.
Exception: For concealed work in finished buildings, or finished panels for prefabricated
buildings where such supporting is impracticable, it shall be permitted to fish the cable between
access points.
 

hurk27

Senior Member
334.17. Revise to read as follows:
334.17 Through or Parallel to Framing Members and Furring Strips. Types NM, NMC, or NMS
cable shall comply with 300.4 where installed through studs, joists, rafters, and similar members.
Grommets or bushings shall be used in metal studs as required in 300.4(B)(1), shall remain in
place during the wall finishing process, shall cover the complete opening, and shall be listed for
the purpose of cable protection.
In both exposed and concealed locations, where the cable is installed parallel to framing
members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable shall
be secured so that the nearest outside surface of the cable is not less than 19 mm (? inch) from
the nearest edge of the framing member or furring strip where nails or screws are likely to
penetrate. Where this distance cannot be maintained, the cable shall be protected from
penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm (1/16 inch)
thick. A listed and marked steel plate less than 1.6 mm (1/16 inch) thick that provides equal or
better protection against nail or screw penetration shall be permitted for this purpose.
Exception: For concealed work in finished buildings, or finished panels for prefabricated
buildings where such supporting is impracticable, it shall be permitted to fish the cable between
access points.

Wow do your drywallers use very short nails/screws lol
 

renosteinke

Senior Member
Location
NE Arkansas
First, a clarification: the wires in the pictures at the start of the thread were definitely not fished. It's a bit hard to see, but in one picture you can see the cable exiting a stud, making a sharp turn toward the wall, then turning again to follow the face of the insulation.

(If you're really sharp. you can also spot all manner of insulation details that would not pass muster today).

Now ... to stir the pot a wee bit ....

Handbook illustrations aside - there have been several instances where the handbook artwork flatly contradicted the text of the code - let's look at that 334.17 language again:

As I read it, it requires wires ruthrough or perpendicular to framing members or firring strips to be either set back or protected by steel.


I hate to say this, but both Iwire's pic and the handbook art sure look like they're showing wires parallel to the firring strips. Where's the set-back or protection?

Is this another instance of the plain meaning of the text being quite different from what they meant to say? Were they really trying to say 'cables penetrating or attached to the framework that will be concealed must be either set back or protected?' Well, that's not what the code says.

As for the 'better idiot' theorum, I see the point. I'm a lot more concerned about that unfused service cable, near a stud and at picture height, than I am about the knee-level convenience circuits. At least I can sleep easy, knowing the convenience circuits are protected by quality FPE breakers- and I hardly ever hang pictures that low.
 

iwire

Moderator
Staff member
Location
Massachusetts
I hate to say this, but both Iwire's pic and the handbook art sure look like they're showing wires parallel to the firring strips. Where's the set-back or protection?

There is no 'set back' requirement.

The requirement is that where NM runs parallel to framing members they have to be 1.25" away from those framing members.

The code is written fine, you are misinterpreting it due to your personal feelings. You are trying to read what you want it to say.
 

Strife

Senior Member
Look at the ADA code. It became a bonanza for lawyers.
Heaven forbid the pitch is 1/128 less than what's supposed to be on a ramp.
Look at the tests doctors put you through to get an aspirin.
It's because "usefull idiots" that think "it can always be better, what about that 1 in a hundred trillionth chance that will happen? We have to MAKE SURE IT DOESN'T Happen"(there, I said it).
The NEC is heading fast toward the same things as above because of "usefull idiots".
20 years from now we'll be spending more times in court rooms than doing electrical work.
And it'll be all thanks to "usefull idiots"(THERE, I said it 3 times)
 

renosteinke

Senior Member
Location
NE Arkansas
Misinterpreting according to my personal feelings? Misread the code? Well ...

You're right, I did misread things a bit. With that qualification of 'where nails are likely to penetrate,' it certainly does look like the practice of running the wires right over the insulation is allowed.

The code is fine? Well, that's the question asked by this thread. I've provided evidence of nails placed away from the studs, in the hanging of paneling- hardly an unusual thing for someone to do. Or, carry it to the other side - place the wires behind the insulation ... where there's a far greater risk, since siding nails will pierce the sheathing everywhere, and not just over studs.

Whether the code is 'fine' is the matter for discussion.

Maybe it is; after all, we don't see that many problems from errant nails. The only one I have dealt with was in a Pre-HUD mobile home, where the NM was run through a notch (rather than a hole) and a screw holding replacement tub molding hit the cable.

It's been my practice - more from laziness than by deliberate choice - to run the cables direct from hole to hole, in the middle of the cavities. Only in rare situations (such as roof trusses or fishing through an existing wall) have I run the cables at the 'face' of a cavity. The picture of the firring strips has certainly made me think.
 
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