Originally Posted By: jgallant This post was automatically imported from our archived forum.
Can someone tell me what rules of thumb there are regarding providing adequate space between non-metallic sheathed branch circuit conductors? A house I inspected today had long runs of conductors (maybe 10) tied in bundles using scrap insulation. See picture.
Originally Posted By: Bob Badger This post was automatically imported from our archived forum.
In the area I work this would fail if it is like this for more than 24"
Once I apply the code I can bundle up to 9 current carrying conductors before derating effects the ampacity of the cable to the extent 12 AWG would end up on 15 amp breakers and 14 AWG would be unusable.
9 current carrying conductors means most times no more that 4 NMs bundled together longer than 24".
Originally Posted By: Bob Badger This post was automatically imported from our archived forum.
lfranklin wrote:
Probably should not ask But here goes....
Are there any type of formula to come up with that 
Remember you asked
First the code section about bundling
Quote:
310.15(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).
Now to figure it out.
Table 310.16 shows 12 AWG copper rated 30 amps.
Table 310.15(B)(2)(a) tells us how much of a downward adjustment Table 310.16 needs for more than 3 current carrying conductors.
4 to 6 conductors gets an 80% cut
30 x .8 = 24 amps This means the 12 AWG is still OK for a 20 amp breaker.
7 to 9 conductors gets a 70% cut
30 x .7 = 21 amps
Still we are OK for the 12 AWG on a 20 amp breaker.
Now lets say we have 10 current carrying conductors, that would get a 50% cut
30 x .5 = 15
Now we have a problem, the 12 AWG is now only rated 15 amps and would require that a 15 amp breaker be used.
The code does not prevent us from bundling we just have to derate the conductor ampacity when we do.
I run a lot of pipe jobs, it is normal for us to run 10 AWG or 8 AWG in raceways for 20 amp circuits when we have 10 to 20 current carrying conductors in one raceway.
In general for 14 and 12 AWG NM circuits 4 is about as many you can bundle and still use the same size breaker.
All this aside some areas ignore these requirements altogether, I doubt that is the case where Ryan inspects.
Originally Posted By: Bob Badger This post was automatically imported from our archived forum.
Greg Fretwell wrote:
Great explaination Bob.
One question I really have never seen an answer to.
How long must you have the cables separated until you can bundle them again for another 23.999"?
How far must they be separated from each other not to be called "bundled"?
Originally Posted By: Greg Fretwell This post was automatically imported from our archived forum.
When I was inspecting I figured if I could get my finger between the cables without moving them they were not bundled. That was based on the distance between the clips on those standoffs they use on furred walls. I haven’t seen anything official. The issue is whether they can “breathe” and not build up heat.
If I was really worried about it I would start worrying about the cables coming out of the top of a panel and going up the wall in a chase or single core of drywall. The energy code mandates that this chase CAN’T breathe.
The entrance into the attic must be sealed against air infiltration. This is not to be confused with firestopping.
Volume does not come into derating. 4 #14s in a 6" pipe gets derated the same as if it was in 1/2".
These are the things that start fights in IAEI meetings
Originally Posted By: jmcginnis This post was automatically imported from our archived forum.
Bob…
This is the type of question I was referring to in the other post about AHJ having the final say according to their interpetation of the NEC. In your post here you said the answer was up to “local interpetation”. In the previous post you said you wouldn’t let the AHJ make you do anything the the NEC doesn’t require specifically. But as you can see in this question, not all the answers are clear and often times are left up to the AHJ to decide. I just wanted to clarify what I meant in the other post and am not trying to be a harda$$.
Originally Posted By: Bob Badger This post was automatically imported from our archived forum.
jmcginnis wrote:
Bob...
This is the type of question I was referring to in the other post about AHJ having the final say according to their interpretation of the NEC. ........ I just wanted to clarify what I meant in the other post and am not trying to be a harda$$.
No problem and I do not think you are being a hard@*+. 
I live in a State that the interpretation is the same across the State. However from reading the forums it is apparent that in other States that is not the case.
I guess one of the things that changes is who the AHJ is. Here in MA the AHJ is at the State level and the inspectors I see are at the city and town level, they can not interpret anything in their own way, they must follow the State AHJ. We also have amendments to the NEC but these are not mysteries they are published and easily followed.
Originally Posted By: Greg Fretwell This post was automatically imported from our archived forum.
Florida is supposed to be the same way, with the Florida unified building code being the final word but it is hard to get opinion out of the inspection process itself.
I am straddling the line since I have ties to the inspector community and my wife is a builder. I see both sides. Builders are a lot quicker to simply say “yes sir” and do things the way a particular inspector wants them than they are to start a poop storm with the state.
When I bring this up to the inspector side they say if the builders didn’t agree they would fight it so they must be right. That is simply not true.
My wife builds in 2 adjacent counties and she has different rules in each county that they must follow although the state law is the same. It is just particular hard ons the county BOs harbor.
Originally Posted By: jpeck This post was automatically imported from our archived forum.
Greg Fretwell wrote:
Florida is supposed to be the same way, with the Florida unified building code being the final word but it is hard to get opinion out of the inspection process itself.
In Florida, the NEC rules on electrical. The AHJ can make interpretations, but put them in writing so they are enforceable and applicable to all.
Quote:
My wife builds in 2 adjacent counties and she has different rules in each county that they must follow although the state law is the same.
How different?
They are (should be, as required by law) the same rules, but may have some difference in interpretation. This is EASILY solved by asking for an opinion from the state, after which they will make a position statement (which is encouraged to be followed, but is not legally binding), then a final declaratory ruling - which is now legally binding.
