Cable derate question (holes in studs)

[anythingyoucanimagine]

I have three NM cables. One #10/2 and two #12/2. 16"OC 2x4 exterior wall. I understand NEC states no ratio of the size of hole compared to the size of the wire. I don't know the rule number but it states something like: "as long as you can pull the wire through the hole without damaging it..."


I need to run the two 12/2 wires through five studs (approx 80"-81") and the #10/2 through two studs (less than 600mm/24"). Can I drill one 1" hole in the center of the studs and run all three cables or should I drill three separate holes? One 1" hole in 3.5" actual leaves 2.5" or 1-1/4" on either side of stud so technically no nail plates required but I will use them regardless since this is a garage.


Alternatively, do put the #10/2 NM through a 3/4" hole and give the #10/2 its own hole above/below? Or... should I give each wire their own hole ~1/2" apart (one cable thickness)? Or... if I use a cable spacer in the center of each stud cavity (such as a 3M SI-1 cable stacker) does that provide enough spacing/cooling to break the bundling?


Any advice on bundling rules? Inspector told me to take good pictures and I can insulate & hang drywall. Just don't want to be taking pictures of code violations...

Thanks.

 

[pattenp]

You can use the one 1" hole. The main thing is to meet the 1.25" from nailing surface, but you said you were going to use protection plates. As you said the hole only needs to be large enough to fit the wire through without damaging the jacket. If you've talked to an inspector you should ask them to be on the safe side.

 

[alfredeneuman]

Any advice on bundling rules?

Wires must be bundled for 24" continuously for the derating factors to apply.

It doesn't apply to holes in studs.

 

[MattT]

Inspector told me to take good pictures and I can insulate & hang drywall.

Write the hole heights on the studs before you take the pictures. Then you'll know exactly where the wires are if you have to do anything in the future.

 

[Jim greengo]

Write the hole heights on the studs before you take the pictures. Then you'll know exactly where the wires are if you have to do anything in the future.

If you're that worried about it use nail gaurds.

 

[pattenp]

If you're that worried about it use nail gaurds.

He said he was going to use nail guards.

 

[alfredeneuman]

Photos would map out the complete routing of the cables for any future reference.
Nail plates would not do that.

 

[Jim greengo]

Photos would map out the complete routing of the cables for any future reference.
Nail plates would not do that.

Who in the world takes a picture of routing of wires?

 

[alfredeneuman]

Who in the world takes a picture of routing of wires?

Me!
I was an electrician for 46 years, and when digital cameras came out I embraced the technology. I took photos of everything I could.
It eliminates the guesswork, and takes only a few seconds more.
I'd provide my customers with copies, and they all appreciated them.

The old adage: "A picture's worth a thousand words" applies.

 

[teamextreme]

Who in the world takes a picture of routing of wires?

Me too! And I used nail plates. I just wish I thought of MattT's idea and wrote the heights on the stud for the pictures, then there'd be no guessing at all when I want to hang a cabinet, or whatever.

 

[ddawg16]

Who in the world takes a picture of routing of wires?

And me.....saved my a lot of headaches more than once

 

[Jim greengo]

Me!
I was an electrician for 46 years, and when digital cameras came out I embraced the technology. I took photos of everything I could.
It eliminates the guesswork, and takes only a few seconds more.
I'd provide my customers with copies, and they all appreciated them.

The old adage: "A picture's worth a thousand words" applies.

I've been doing it for a really long time myself,never had the need to take a picture to remember where things are.
1 circuit for each room/outlet boxes at 16" to bottem/switch boxes at 48" to top,and I hold my drill waist high and just work my way around the room.
I'm pretty sure I've done it more than once with my eyes closed,maybe I've just been doing it too long?

 

[alfredeneuman]

I did mostly commercial service and construction work. They were all "one-offs" never to be repeated. Unlike you I couldn't work with my eyes closed.
Production work like that must have proven to be extremely boring.

 

[alfredeneuman]

It saved me time also with later questions of what I did if the customers had photos.
They would be able to use the photos for subsequent trades to avoid the wiring, and also for bidding purposes.

 

[checkthisout]

Wires must be bundled for 24" continuously for the derating factors to apply.

It doesn't apply to holes in studs.

Where does it apply say in a typical residential electrical job?

 

[alfredeneuman]

NM, SER etc. with no air space between the jackets for more than 24"
Conduit used for NM and for protection of multiple runs of cable

 

[Jim greengo]

I did mostly commercial service and construction work. They were all "one-offs" never to be repeated. Unlike you I couldn't work with my eyes closed.
Production work like that must have proven to be extremely boring.

I've done plenty of custom houses,same way
I quit doing big commercial/ industrial stuff long ago when I had a crew to do that stuff.
Too many rods/screws and now arthritis in my body to bend pipe all day,bent miles of emt and rigid when I started out though.

 

[anythingyoucanimagine]

Sorry to post and then go MIA. We were supposed to sneak up to our cabin for a few days and as it turns out I've spent the last few hours holding her hair out of the toilet (she's sick).


I didn't mean "one-inch hole is fine, shove'em through" The nec is very specific about cable spacing and bundling yet at same time (in my mind) extremely vague. If I am running two nm-b (#12/2 with ground) cables through five (5) studs and at same time I want to run a NM-B #10/3 less than 24" (the 10/3 is with ground and neutral is not used but could be conductor in future). I meet the NEC for the run of the two 12/2. The #10/3 is shorter than 24". Does the "shove'em in... as long as the jacket doesn't tear" rule apply and that's it?

Thanks.


edit: is an inspector going to bust my balls over this?

 

[TRWham]

Who in the world takes a picture of routing of wires?

For us it's not the wires- it's the boxes. Every job the drywallers cover something up and having the photos saves headaches looking for them and drywall repair as the sparkies make holes looking.

 

[Jim greengo]

I usually try to keep boxes an equal distance as far as spacing goes,and centered on a wall as close as possible on the wall.

If my 12' doesnt land center,I usually a box and make them same distance from end of wall.
Again it makes it easier to tell where a box is supposed to be and since I always use same elevation for certain boxes that helps also.

 

[Innovate1]

I take lots of pictures too. Saved me with more than wiring. And made a number of jobs later much easier. The people who poured the basement floor in my house got enough fines in the traps to plug the floor drains solid. You know you are in trouble when someone on the crew says they are a man short because someone had to see their parole officer! Glad I had some pictures of where the heating tubing was when they had to cut out a small section of the floor to replace the trap. managed to avoid cutting the tubing.

 

[anythingyoucanimagine]

I wish someone would please be able to help me with my question.

At this point it is a moot point --I drove the (hour round trip), used extra nail plates, drilled a 3/4" hole (each 3/4" apart) for each NM-B wire and that's that. I also took LOTS of pictures. If an inspector ever tried to make me open up that wall I'd let him (or her) cut me off from PoCo and take it to court before I touch that drywall.


I'm still curious though: 80" of 12/2 passing through studs, that's 4 conductors and under derate requirements. One additional short (less than 24") length of 10/2 --that makes 6 conductors but for less than 24".


What would (should) one do to be compliant? (nec2017)

thanks.

 

[TRWham]

I wish someone would please be able to help me with my question
... If an inspector ever tried to make me open up that wall I'd let him (or her) cut me off from PoCo and take it to court before I touch that drywall.
...
What would (should) one do to be compliant? (nec2017)

thanks.

You should get your rough electrical inspection prior to closing the wall and there will be no issue of opening anything later. Nothing gets closed until first all the mechanical rough inspections and then the framing inspection are complete. Then you can hang your drywall.

 

[PCustoms]

You should get your rough electrical inspection prior to closing the wall and there will be no issue of opening anything later. Nothing gets closed until first all the mechanical rough inspections and then the framing inspection are complete. Then you can hang your drywall.

This. Are tough subject to inspection?

Also your original questions was answered, you are compliant. For (your) piece of mind and just to make the pull easier, why not offset the hole for the 10/2 6" and drill 2 more?

 

[mm08822]

I wish someone would please be able to help me with my question.

At this point it is a moot point --I drove the (hour round trip), used extra nail plates, drilled a 3/4" hole (each 3/4" apart) for each NM-B wire and that's that. I also took LOTS of pictures. If an inspector ever tried to make me open up that wall I'd let him (or her) cut me off from PoCo and take it to court before I touch that drywall.


I'm still curious though: 80" of 12/2 passing through studs, that's 4 conductors and under derate requirements. One additional short (less than 24") length of 10/2 --that makes 6 conductors but for less than 24".


What would (should) one do to be compliant? (nec2017)

thanks.

The first two replies to your post answered your concern about de-rating. Done!

Just a note for future reference - You put yourself in a vulnerable situation closing up the walls and then providing pics to be later scrutinized – electrical or otherwise. Your sheetrock and insulation are at risk following this practice.

As for all the sidebar discussions about pics needed/suggested, etc.……welcome to GJ! Now you understand how thread size grows by a factor of 10.

Back to the derating topic………..you started with two 12-2 and one 10-2 NM-B cables passing thru a hole.
If derating were applicable here:
There are 6 current carrying conductors overall in the NM-B cables (90C THHN Cu).
4-6 conductors get derated to 80% of their 90C value.
Ampacity of #12 THHN @90C = 30a and #10 THHN@ 90C = 40a. However 12’s can’t be ocp’d above 20a and 10’s can’t be above 30a.
12’s – 30a x .8 = 24a, but 20a ocp max, so 20a cb = ok.
10’s – 40a x .8 = 32a, but 30a ocp max, so 30 a cb = ok.

 

[Jim greengo]

This. Are tough subject to inspection?

Also your original questions was answered, you are compliant. For (your) piece of mind and just to make the pull easier, why not offset the hole for the 10/2 6" and drill 2 more?

 

[Jim greengo]

The first two replies to your post answered your concern about de-rating. Done!

Just a note for future reference - You put yourself in a vulnerable situation closing up the walls and then providing pics to be later scrutinized – electrical or otherwise. Your sheetrock and insulation are at risk following this practice.

As for all the sidebar discussions about pics needed/suggested, etc.……welcome to GJ! Now you understand how thread size grows by a factor of 10.

Back to the derating topic………..you started with two 12-2 and one 10-2 NM-B cables passing thru a hole.
If derating were applicable here:
There are 6 current carrying conductors overall in the NM-B cables (90C THHN Cu).
4-6 conductors get derated to 80% of their 90C value.
Ampacity of #12 THHN @90C = 30a and #10 THHN@ 90C = 40a. However 12’s can’t be ocp’d above 20a and 10’s can’t be above 30a.
12’s – 30a x .8 = 24a, but 20a ocp max, so 20a cb = ok.
10’s – 40a x .8 = 32a, but 30a ocp max, so 30 a cb = ok.

 

[checkthisout]

I wish someone would please be able to help me with my question.

At this point it is a moot point --I drove the (hour round trip), used extra nail plates, drilled a 3/4" hole (each 3/4" apart) for each NM-B wire and that's that. I also took LOTS of pictures. If an inspector ever tried to make me open up that wall I'd let him (or her) cut me off from PoCo and take it to court before I touch that drywall.


I'm still curious though: 80" of 12/2 passing through studs, that's 4 conductors and under derate requirements. One additional short (less than 24") length of 10/2 --that makes 6 conductors but for less than 24".


What would (should) one do to be compliant? (nec2017)

thanks.

So I had to come back revisit this.

Wires are considered "bundled" if they are passing through a hole that is be firestopped I.E. caulked, foamed or fiberglassed shut like you would find in a header.

Or,

If they are passing through the same hole in a stud cavity that is to be insulated. In other words you have a wall and you drill a single hole through each stud run wires through the holes and then insulate the wall, that is considered bundling.

So what the hell does that mean to you? You're fine with 3 cables per hole at the typical breaker size you would normally use for the wire gauge. I.E. 30 amps for 10 gauge, 20 amps for 12 gauge and 15 amps for 14 gauge.

 

[mm08822]

So I had to come back revisit this.

Wires are considered "bundled" if they are passing through a hole that is be firestopped I.E. caulked, foamed or fiberglassed shut like you would find in a header.

Or,

If they are passing through the same hole in a stud cavity that is to be insulated. In other words you have a wall and you drill a single hole through each stud run wires through the holes and then insulate the wall, that is considered bundling.

So what the hell does that mean to you? You're fine with 3 cables per hole at the typical breaker size you would normally use for the wire gauge. I.E. 30 amps for 10 gauge, 20 amps for 12 gauge and 15 amps for 14 gauge.

You're right.....that's in 334.80.
The derating however doesn't have an impact until you exceed 9 ccc in total for nm-b.

 

[anythingyoucanimagine]

Sorry. You guys started going back and forth about taking pictures and I must have skipped over the answer.

mm08822: Thanks. checkthisout: Also thanks.

TRWham: My prior experiences are exactly as you describe... As homeowner you APPLY for a permit, you don't "pull permits". It's not your god-given right to "pull" a permit for anything you want. Back home at my ahj, usually if you can submit a halfway decent permit application they approve it. In my experience they are usually more friendly/nice/lenient with homeowners who aren't trying to cut corners and have half-a-clue. Either way yes --my experience is typical rough/final as you describe.


I have two problems. First, our house at home is 3ph 208Y. This is my first time working with split phase 120/240. Second, this is different ahj and this guy (inspector) is a bit of a mess. One day he's totally fine and the next day it's like he got up on the wrong side of the bed and he's looking to nit-pick over anything he can. We bought the house with a revoked CO due to electrical issues. He let me set up a temporary panel on a board (similar to a new home construction or job site) then he's letting me wire in the actual meter/panel/service entrance and do the garage before I do the rest of the house. So essentially do the house in two steps, first panel & garage, then rest of the home. By doing the garage first it lets me use tools, keep the heat/hvac on, run extension cords into the house, etc. So it is "sort of" a traditional rough/final inspection process...


PCustoms: That's what I did. Inspector said I could put up insulation & drywall as long as I took pictures (of work done correctly). I know technically I didn't need nail plates for 1/2" or 3/4" hole in center of 2x4 but I used nail plates anyway. I drove the 1hr round trip, bought some nail plates and ran them each through their own holes. Done. There's no rule that says you can't exceed code...



Thank you everyone for all of your help. Much appreciated!!

 

[Jim greengo]

Us licensed contractors "apply " for permits also,it says permit application on top of the form every time I fax 1 in to the city.

 

[checkthisout]

Electrical in our state is simply a purchase online system. You don't apply for the permit but simply buy it.

 

[anythingyoucanimagine]

Us licensed contractors "apply " for permits also,it says permit application on top of the form every time I fax 1 in to the city.

LOL --yeah but I'm an idiot homeowner. Honestly I'm probably more ****/ocd about code and having everything perfect than all you "time is money" guys.

I have lots of friends in various trades. They pull permits and hang their licence on the job. I (as homeowner) submit project plans and apply. I have a buddy who blew out his back so I helped him for about 6 months (pretty much as his *****). He didn't apply for permits like I apply for permits. Irony is the only difference between he & I is about $1,200 (state registration and insurance). He's also had a GC registration for 13 years (always in good standing). Not sure how far that goes at the inspector's office.


In my experience usually they get Tradesman (or women), clueless homeowners and OCD/**** pain in the *** homeowners --I probably fall into that last category.