max NM in hole thru joist - Electrician Talk - Professional Electrical Contractors Forum

stillirnin · 09-23-2009, 07:23 AM

Which article will cover how many cables can run in a hole in a joist and dia. of hole. thanx in advance

mcclary's electrical · 09-23-2009, 08:11 AM

Quote:

Originally Posted by stillirnin

Which article will cover how many cables can run in a hole in a joist and dia. of hole. thanx in advance

If you're not fireproofing, then you would not need to worry about it. The limitations start when hole is to be firestopped. If MORE than TWO NM cables pass through a hole that is to be firestopped, then you derate to 310.15. (B) (2) a. So there is no limit on the number, but rather on the current each conductor will be rated for after derating.

oh yeah, this comes from 334.80

raider1 · 09-23-2009, 11:44 AM

I agree with Mcclary's electrical.

There is no NEC code limit to the number of NM cables installed through bored holes in joists. You just need to watch the adjustment factors if the holes are to be fire or draft stopped.

Keep in mind that when starting you adjustment in accordance with 334.80 you can start your adjustments at the 90 degree ampacity column.

Chris

s.kelly · 09-30-2009, 10:28 PM

I do not think it is what you are asking, but there are framing limits about size and placement of holes in joists. UBC and IBC I think are the relavant codes, but I might be remembering wrong.

Rarely are electricians the issue here, but I have seen plumbing thru holes or notches that were really scary.

captkirk · 09-30-2009, 10:35 PM

Quote:

Originally Posted by s.kelly

I do not think it is what you are asking, but there are framing limits about size and placement of holes in joists. UBC and IBC I think are the relavant codes, but I might be remembering wrong.

Rarely are electricians the issue here, but I have seen plumbing thru holes or notches that were really scary.

Thats soo true. I get nervous about drilling a one inch hole

luminous · 10-01-2009, 01:53 AM

I was taught you can drill on the outer two thirds but never on the center third,,hmm,not sure how much structural support can be removed at those points, there must be a formula for this,not sure,I always played it safe (AS LITTLE AS POSSIBLE)

mcclary's electrical · 10-01-2009, 05:41 AM

Quote:

Originally Posted by luminous

I was taught you can drill on the outer two thirds but never on the center third,,hmm,not sure how much structural support can be removed at those points, there must be a formula for this,not sure,I always played it safe (AS LITTLE AS POSSIBLE)

That's weird,,,,,because that is the EXACT OPPOSITE of what you should be doing. Always drill in THE MIDDLE 1/3. NEVER DRILL the outer 2/3. Someone told you wrong. You would fail rough in inspections everytime with your method

Bob Badger · 10-01-2009, 06:05 AM

Quote:

Originally Posted by raider1

I agree with Mcclary's electrical.

There is no NEC code limit to the number of NM cables installed through bored holes in joists. You just need to watch the adjustment factors if the holes are to be fire or draft stopped.

Keep in mind that when starting you adjustment in accordance with 334.80 you can start your adjustments at the 90 degree ampacity column.

Chris

I agree with Chris but will add that many inspectors feel that a number of cables running trough the same holes in a number of joists or studs in a row is bundling when done for more than 24" and you would have to apply the derating rules. I agree with those inspectors.

mcclary's electrical · 10-01-2009, 07:59 AM

Quote:

Originally Posted by Bob Badger

I agree with Chris but will add that many inspectors feel that a number of cables running trough the same holes in a number of joists or studs in a row is bundling when done for more than 24" and you would have to apply the derating rules. I agree with those inspectors.

Unless the hole is 24" deep,,,,,that's not bundling. Bundling is together for 24",,,,,,,period. So once you go through hole and then hit stackers,,,,,there is no bundling. Like I said, unless the hole is 24" deep

Mr. Sparkle · 10-01-2009, 10:22 AM

Quote:

Originally Posted by mcclary's electrical

Unless the hole is 24" deep,,,,,that's not bundling. Bundling is together for 24",,,,,,,period. So once you go through hole and then hit stackers,,,,,there is no bundling. Like I said, unless the hole is 24" deep

I agree with you even though I think in "UL" terms we are both wrong and it does say it to derate after a certain number of cables are installed right on the bag of stack-its.

Bob Badger · 10-01-2009, 11:27 AM

Quote:

Originally Posted by mcclary's electrical

Unless the hole is 24" deep,,,,,that's not bundling. Bundling is together for 24",,,,,,,period. So once you go through hole and then hit stackers,,,,,there is no bundling. Like I said, unless the hole is 24" deep

Well I disagree with you that it has to be in a 24" long hole to be bundled.

So I will ask you to take a look at Exception 5 to 310.15(B)(2)(a) and explain to me why that exception was necessary if what you say was true?

That exception make clear the CMP considers cables run through bridle rings as 'bundled' and those bridle rings might be as much as 6' apart.

mcclary's electrical · 10-01-2009, 11:32 AM

Quote:

Originally Posted by Mr. Sparkle

I agree with you even though I think in "UL" terms we are both wrong and it does say it to derate after a certain number of cables are installed right on the bag of stack-its.

I've never seen a bag of stackers say that. The were designed for that EXACT reason. The article about bundling says something like (i don't have my book with me) "unless seperated for air space",,,,,,and that's what a stacker does.

raider1 · 10-01-2009, 12:44 PM

Here is what 310.15(B)(2)(a) says:

Quote:

(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 installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

So the question becomes what spacing is required before this is no longer bundling?

Chris

Mr. Sparkle · 10-01-2009, 01:45 PM

Quote:

Originally Posted by mcclary's electrical

I've never seen a bag of stackers say that.

Look closely, unless it's been ratified recently it says right on the bag "When installing more than (4) 2 wire cables derating should be considered." or something very similar.

I don't agree with it, I am just a fountain of useless information sometimes.

luminous · 10-01-2009, 02:16 PM

mcclary I'm not a residential electrician, so I took your (you were taught wrong) serious for future info,but I also did a little research and all the info I got says I was taught right,please find something telling me otherwise,I do want to know the truth of the matter, thanks

Drilling and notching of standard wood members is subject to the following:

Notches in joists, rafters, and beams may not exceed one-sixth of the depth of the member, may not be longer than one-third of the depth of the member and may not be located in the middle third of the span.

Notches at the ends of a joist, rafter, or beam may not exceed one-fourth the depth of the member.

The diameter of holes bored or cut into joists, rafters, and beams may not exceed one-third the actual depth of the member. Holes may not be closer than 2 inches to the top or bottom of the member or any other hole located in the member. Where the member is also notched, the hole may be no closer than 2 inches to the notch.

luminous · 10-01-2009, 08:09 PM

After conferring with the lead EE at the university,he replied that he wasnt sure that he will find out for me,and told me common sense tells him since the outer perammeter is stabilized by the foundation that the weaker area would be the most centralized area away from the last support since most joist just use a vertical beam, and removing support from that location would in fact make it weaker as opposed to the outer two thirds supporting less weight,

Magnettica · 10-01-2009, 08:19 PM

Violation?

Black4Truck · 10-01-2009, 08:24 PM

The conductors are in "free air"

BUT as they pass through the 1/2 inch web they are touching

mcclary's electrical · 10-01-2009, 09:43 PM

Quote:

Originally Posted by luminous

mcclary I'm not a residential electrician, so I took your (you were taught wrong) serious for future info,but I also did a little research and all the info I got says I was taught right,please find something telling me otherwise,I do want to know the truth of the matter, thanks

Drilling and notching of standard wood members is subject to the following:

Notches in joists, rafters, and beams may not exceed one-sixth of the depth of the member, may not be longer than one-third of the depth of the member and may not be located in the middle third of the span.

Notches at the ends of a joist, rafter, or beam may not exceed one-fourth the depth of the member.

The diameter of holes bored or cut into joists, rafters, and beams may not exceed one-third the actual depth of the member. Holes may not be closer than 2 inches to the top or bottom of the member or any other hole located in the member. Where the member is also notched, the hole may be no closer than 2 inches to the notch.

In my response, I was speaking of drilling a hole, not a notch. So the first two do not apply. But the third one actually backs up my statement. It says "may not be closer than 2" from the edge. So this FORCES you to DRILL A HOLE, not a notch, in the MIDDLE 1/3.

mcclary's electrical · 10-01-2009, 10:11 PM

Quote:

Originally Posted by Magnettica

Violation?

This is a good example of the code being vague. I see "air space",,,,,but do you call this "maintaining spacing",,,,and what does that mean? and how much spacing?