NM cable thru studs

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tom baker

tom baker

First Chief Moderator & NEC Expert
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Master Electrician
A question came that I want to refer to the forum members. In our area, we are limited to 3 runs of NM cable (example 12-2 w/G)thru a drilled hole in a wood stud. What is the NEC basis for the limit of 3 runs of NM cable?
 
Re: NM cable thru studs

that specific requirement is not, NOT, in the NEC. It came from some construction technology teachers and is a misapplication of code. Ask the inspector to find it. It can't be done.

The attempted logic is bundled wiring and conduit fill. The proof is in the limitation. It allows any 3 in any hole. 4 14-2 in 2" hole is not okay by them. 3 6-3 in 3/4" hole is legal by them.

It is/was in the area I worked. I was always doing the remodels where there was some inspector discretion where to termnate and what to allow, SO.....I didn't argue. The inspector that enforced that came from the local JC tech course. I also inspected for a bit in an area where most of the other inspectors came from a tech course in the JC, and many of them were also taught that bs about 3 holes.

The tech courses don't seem to include teachers with actual building experience.

Any tech course teachers out there???????? :cool:

paul
 
Re: NM cable thru studs

It is from the AHJ and, I would assume, they have gotten it from 310.(B)(2)
Adjustment Factors. (a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a).
Click to expand...
In my opinion, a blanket rule is wrong and each case should stand or fall on its own merits. :D
 
Re: NM cable thru studs

San Francisco used to have a rule that only one cable was allowed in a hole. Not sure if that is true currently. Best to check with the inspector before starting work in a jurisdiction where you haven't worked recently.
It's usually easier to comply with an oddball rule than to fight over it.
I have often won an inspection argument by asking the inspector to cite a code section. They usually can't.
 
Re: NM cable thru studs

heck of a stud, 24" thick. In the same jurisdiction in which i was an electrician, on one of the last remodels i did, the inspector made me bundle all the old feeds in one stud bay, not quite 8'. not over 3 in one hole, but bundle all the wires. go figure.

not all runs of romex are feeds. a single circuit hall switching scheme can involve quite a few 3 & 4 ways, switch legs. some high end houses need a 4x4x2 with a 1&1/2" extension just to handle the wire fill for 2 switches.

paul
 
Re: NM cable thru studs

Bill, I don't work in SF much (thankfully) but I understand the one cable per hole to be the local rule. But hay, the mayor would probably let you marry a tree, so I figure sanity might not be involved. It's a real shame the place is known around the world and has become such an embarassment. :(
 
Re: NM cable thru studs

Politics aside, San Francisco is a wonderful place to visit. It is a beautiful city and, it seems, almost everyone is very friendly (just like other places in the US . . . including New York City). I have been to San Francisco just a couple of times, fell in love with the place, and am ready to go back. I love the bread bowls at Bodines. :D
 
Re: NM cable thru studs

I guess being around here for 40 years I don't appreciate the place as much as Indianapolisites do. I'm only about 15 minutes away and I don't go there much but there are some places and things there I like to go and do. I don't know of Bodine's, I'm guessing it's on the warf?

[ November 15, 2004, 04:37 AM: Message edited by: physis ]
 
Re: NM cable thru studs

There is one in the financial district plus one at the end of the street car line and close to one of the piers. Since they have a store in San Diego, I would assume there are more in San Francisco. They have several different soups available that they put into the center of a small loaf of sourdough bread and it becomes the bowl. :D
 
Re: NM cable thru studs

Charlie, are you describing a bread bowl for me? You know real sourdough can only be made here don't you. :p :cool:
 
Re: NM cable thru studs

physis: i didn't know there was anywhere that was 15 min from the city during commute hours.

If you are not apprecating SF's ambience, try this list of activities:

give yourself a day at the exploratorium, no fudging, all day with a local lunch. one of the few places with operating Tesla equipment ( i forget the name of the generator), go with a friend if you can.

Give yourself a week to find ALL the parks in the city. get a list with addresses. there might be a few you don't want to do.

take a small back pack for street tennies, start at the top of the GG park and rollerskate with all the others to the ocean, take a cab or bus back to your car after trating yourself to an ocean view snack, meal, drink, or whatever.

give yourself a year to find the best view of the city from an elevated restaurant. start at the Top of the Mark, just a drink, if you do that, if you don't want to eat.

Find all the buildings with extant 30's murals, including coit tower.

spend lunch for a week at the cliffs below the palace of legion of honor.

visit ALL the museums, including the ones in the second exercise.

Plan a complete retirement in Indiana ( my apologies to those from that illustrious state).

the problem with living around the bay area is that we get used to it and only complain about parking or traffic. Does sf still have the "great parking race"? I don't imbibe anymore, but there are tons of places to enjoy that activity with great views, scenery and otherwise.

or for a great view of the city, go to the once-a-month antiques flea market on the tarmack at the ex-naval air station on Alameda. (1st sunday of the month. it fills up the whole "jet" tarmack with sellers and buyers. only place to find some OLD electrical testers cheap.)

and sf is one place where the electrical inspectors usually are very good at what they do, if a little over zealous about permits for changing light fixtures.

paul
 
Re: NM cable thru studs

Hi Tom,

Back to reality. There are well known problems in pulling 3 bundled nm cable runs through any stud framing. It's an electrician's rope pulling knowledge about multiple cable outer sheathing burn from jammed overfill through even a 7/8" hole.

This is one good reason that no more than two bundled romex is a limit in long runs and around corners. I have done production work and pullers really yank fast to meet deadlines. When an AHJ spots wall runs with exposed conductor primary jackets, they get out a tag. I've seen a two bundle limit in some jurisdictions.

As far as a second reason, NEC 310.15 derating factors come into play when over three or more current carrying conductors (not including neutral or return circuit conductors) are bundled for over 24" length runs. Running two 14-2's and one 14-3 through the framing become non-compliant unless there are travelers involved. I have never convinced an AHJ on compliance in this configuration. They don't have the time to track down a run to verify it. I usually acknowledge good practice in workmanlike conditions up to three nm pair bundles of 14 & 12 AWG as the limit.

The cable fill illustration in my book on page 31 is a scaled example. Sorry I haven't sent you the 2005 copy. I have decided to code flag reference the whole book and it really is a time consuming effort. Color is being worked on but still not a priority.

rbj, Seattle

[ November 15, 2004, 10:29 PM: Message edited by: gndrod ]
 
Re: NM cable thru studs

Paul, most of the things you mention are fine examples of things to do in the City. At least half of them are things I still do occasionally.

You will not, however, get me to agree with you about the building department. I would guess you may not have had the comparitive pleasure of working somewhere more civilized.
 
Re: NM cable thru studs

gndrod: still not in nec, rules for production pullers is not enough to flag independents like myself. the rule is for wires bundled for 24", not thru studs. it has nothing to do with production pulling techniques. misapplying sections is still an error. bundled runs are still only derated, not against the code. It has to do with cooling, not blind pulling. interior walls are almost never insulated so there is room for wires to cool when they might get warm. If this were a real problem, how we wire panels with all those wires so close to each other must be a problem waiting to be discovered. allowing multiple wires thru large romex connectors must be slipping by all those tech scool boys.

physis: i was just lucky, i guess, only worked for others when in the city, but only failed once for not knowing local rules for fire alarm circuits. 15 min must be marin or so.sf.

what i did like was the red and black rule for phases. What are your complaints besides the ongoing nepotism and influence scandel, or has that already been whitewashed?

paul :)
 
Re: NM cable thru studs

grndrod: it is not an exception. the rule for bundled wires is for wires bundled for 24" or longer, not bundled at any point. for me to find an exception to a rule that does not exist (wires bundled for any length) is impossible. charlie posted the info at the beginning of this post. go back to the start of the post.

and again it is only a derating, not a prohibition.

most residential inspectors that i have met (where the inspectors were all trade inspectors)cannot even do wire fill calcs, let alone understand derating, and i is (was, am) one.

somewhere in the beginning of the nec it states that you cannot bargain shop the rules (mix and match). Or it used to.

paul :roll:
 
Re: NM cable thru studs

apauling,

So what I understand is that you have pulled 4 cables together and calculated the bundle below the derating limit while running the bundle parallel to 25" horizontal galvanized iron DWV plumbing. Lets use an outside wall that is blown insulated. How do you convince the AHJ? I know SF uses copper plumbing so maybe you don't see the iron scenario such that exists in say, Sacramento County.

not bundled at any point.
Click to expand...
BTW, we are talking free air, not stud thickness. The three bundle rule also applies in attic parallel bundle runs in some AHJ's. (Nevada, Placer Co.s if I remember.)I can't visualize residential new construction in SF. It's all remod unless there's projects up in the Twin Peaks area. ;)

rbj, Seattle
 
Re: NM cable thru studs

if this is about you imagining me doing what what you want me to do so you can criticize it, have fun, go talk to youself in the bathroom mirror. if it's about the application of the nec or elec questions i feel that i can respond with clarity without it being about something else.

If it's dundled for 24" then it falls under the requirement for derating. But wiring comes together at various points all over in residential construction and it does not automatically come under the derating rule. You might as well imagine that you can't cross two bundles of three wires without derating.

If you want to imagine me saying things i didn't, just have the conversation in your head, leave me out of it.

and it ain't in the nec

paul ;)
 
Re: NM cable thru studs

Bundling is not prohibition, just realize that derating must be proven to comply to the adjustment factors of 310.15(B)(2)(a)

rbj, Seattle

[ November 16, 2004, 02:07 AM: Message edited by: gndrod ]
 
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