Thread: Bundling in outside walls

I keep seeing where the electrician takes all of the wires going from the panel box in the basement through the first floor in 1-2 BUNDLES of 6-8 wires that will be in an outside INSULATED wall up to the second floor or beyond.

I interpret this as having the wires in a RACEWAY, and you can't have more than 4-current carrying conductors in a raceway bundled for more than 24" without derating the wires...

Although not a CODE inspector, I point to 310.15 (2) Adjustment factors.

Does someone have a better reference, brochure, example that I can give to builders...

The two pictures were from the same house, the bundle was on the first floor, the spread out wires were DIRECTLY above the bundle and is what I generally prefer to see. The electricians see to think that if they use those standoff spacer things that the rules don't apply...those are fine for INSIDE WALLS and open air uninsulated cavities...

The WORST case of bundling was 2 bundles of 8 wires each, including the attic heat pump Aux-heat circuit, Attic furnace circuit, the bathroom heaters, the washer & dryer circuits, outside flood lights and all of the bathroom, wall and lighting circuits...Oh yes, and they were wire-tied every 18" to boot... Looked really nice and neat

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Originally Posted by Bob Sisson

I keep seeing where the electrician takes all of the wires going from the panel box in the basement through the first floor in 1-2 BUNDLES of 6-8 wires that will be in an outside INSULATED wall up to the second floor or beyond.

The "6-8 wires" ... is that 6-8 "current carrying conductors" or 6-8 "NM cables?

The one photo showing the three separate NM cable is great ... depending on what type of exterior cladding is being installed. If the exterior cladding is siding and is to be installed nailed to the studs, then that is no problem, however, if the exterior cladding is going to be stucco, then you have another problem as the metal lath will be nailed to that OSB surface, making that entire surface the nailing surface, meaning the NM cables would need to be back 1-1/4" from that surface. Now, how about when a WRB is nailed to the OSB ... ? Yes, the NM cables should be kept back 1/1-4" from the inside surface of the OSB.

I interpret this as having the wires in a RACEWAY,

Nope.

Not in a raceway.

and you can't have more than 4-current carrying conductors in a raceway bundled for more than 24" without derating the wires...

That does not apply to cables, however, cables have their own limitations, when more than one multi-conductor cables are bundled or lack of maintaining spacing, etc., the net result is the same. A multi-conductor cable has at least 2 conductors in it, two multi-conductor cables makes 4 conductors - same problems arise.

Although not a CODE inspector, I point to 310.15 (2) Adjustment factors.

Very good, but I would address it properly. It *is not a raceway*, however, *there are more than one multi-conductor cables* there, so now you have to look at it further to see what applies.

In the photo with the three cables, I'd write up the lack of clearance from the nailing surface.

The other photo creates its own problems while solving the 1-1/4" clearance problem.

Those straps are designed to locate the NM cables the correct distance back from the edge of the stud - that is good.

Those straps are also designed to locate the NM cable separately from each other and to "maintain spacing" - that is also good.

However, those straps are also designed to have one NM cable in each slot, not two as shown in the photo - that is not good.

It also looks to me like they need to use more of those straps, not because they are too far apart to meet minimum code requirements, but because they are too far apart to keep the NM cables back from the edge of the studs. *Could* the electrician correct that by taking more time in running the NM cables? Sure, or thy would simply throw in a few more straps - their choice. The requirement for supporting and securing is very nicely meet with those straps, the requirement for clearance from the nailing surface is not, not as installed.

Then, in that second photo, there is also that lonely single NM cable running up in the corner saying 'Come on, I dare you, drive a nail in me.' - someone will very likely take that dare up ...

You are who I was hopping was going to respond...

My concern is that up here in the north, that cavity is going to be filled, probably stuffed, with insulation shortly. Any space between the wires except right at the standoffs is gone, and the insulation will do its best to contain any heat generated by the bundle within the bundle...

Its not a raceway...OK... It is an enclosed non-ventilated tight space. I would have no problem (until you mentioned 2-wires in 1-slot) if this were in an inside partition wall with nothing but air around it...

Can I say...

When three or more multi-conductor cables are bundled or stacked longer than 24" without maintaining spacing they must be derated appropriately. Enclosing multiple NM cable within an insulated cavity even while supported by separating standoffs does not provide for the airflow needed to maintain the cables ampacity. The cables need to be spread out so that they do not contribute to each others heating.... This is supported by Article 310.15 (2) of the NEC... (please re-write to your content...)

The wires that were stapled to the sheathing were on the BRICK side that had already been bricked.. so no new nails... but good point if they do something similar on a wall to have siding added later (oh..metal siding..ouch) I will remember that for the next one...

What you thought was a wire is a bead of foam tucked in the corner

I sent a picture like this to ICC last year for an interpretation and they agreed with me saying it was wrong, but they never gave me better "generic" wording that I can use when I see bundles like this, with or without the standoffs...

A thought... but again once it is surrounded by insulation I wonder about the "spacing"...

If they took those (in this case) 6-NM cables and put them on 2-Three-slot NM standoffs on OPPOSITE SIDES of the Stud cavity, it would be much better... when the number of wires gets large, insulating behind the standoffs becomes another issue, and I have only seen 5-tier standoffs...well, that would be 10 wires (R & L) PER CAVITY... I have seen 5 in one cavity, and the 5+5 in the next... if they were PROPERLY put on the standoffs so they don't get mushed together by the insulator it MIGHT be a solution...


What say you?

Those spacers look like the Stak-its from 3M. The package lists them for use with 1-8 #14 gauge cables and 1-4 #12 or #10 cables.

Bob, you need to remember that the derating factors are based on the 90 degree column for NM cables. Table 310.15(B)(2)(a) lists the ampacity adjustment factors for 4-6 current carrying conductors at 80%, 7-9 at 70%. Fourteen gauge wire has a 90 degree ampacity of 25 amps. 25 amps x .8 = 20 amps, 25 x .7 = 17.5. This is still above the maximum that #14 can be protected at which is 15 amps. Your need for derating issue is a non-issue, it is fine unless I am not seeing some cables. I am seeing 3 #14s and 1 #12 in the stackers.

Originally Posted by Jim Port

Bob, you need to remember that the derating factors are based on the 90 degree column for NM cables. Table 310.15(B)(2)(a) lists the ampacity adjustment factors for 4-6 current carrying conductors at 80%, 7-9 at 70%. Fourteen gauge wire has a 90 degree ampacity of 25 amps. 25 amps x .8 = 20 amps, 25 x .7 = 17.5. This is still above the maximum that #14 can be protected at which is 15 amps. Your need for derating issue is a non-issue, it is fine unless I am not seeing some cables. I am seeing 3 #14s and 1 #12 in the stackers.

Bob,

Those exterior wall stud cavities get insulated all over, down here too.

In addition to what Jim pointed out, the derating for bundling is taken from the chart ... after applying the derating for ambient temperature first.

Thus, Jim's calculation would be as follows:
Presuming ambient is at times 96 degrees F or greater on that wall and within that insulation which we KNOW is going to be there, and presuming that it will not get hotter than 104 degrees in that wall (and it very well *might* if an east, south or west facing wall) the derating multiplier factor for that ambient temperature range would be 0.91.

As Jim said, "Table 310.15(B)(2)(a) lists the ampacity adjustment factors for 4-6 current carrying conductors at 80%, 7-9 at 70%. Fourteen gauge wire has a 90 degree ampacity of 25 amps. 25 amps x .8 = 20 amps, 25 x .7 = 17.5." ... times the ambient derating factor of 0.91 = 15.9 amps ... which is still within the protection of a 15 amp breaker - all is well and good.

Now, however, let us presume that the ambient in that wall is 105 degree to 113 degrees, as it very well could be, as stated above. This makes the ambient derating multiplier 0.87. That makes the equation look like this: 25 amps x 0.87 ambient multiplier = 21.75 x 0.7 derating for lack of spacing = 15.2 ... which is still within the protection of a 15 amp breaker.

Here is the kicker, though, for get the wall temperature if those NM cables go into the attic, you now need to apply the attic ambient derating multiplier.

Presuming a typical attic gets to be between 132 degrees and 140 degrees in the summer (and we've already in the past had discussions from everyone about how hot it gets in the attic, some have even posted well over 140 degree, so the 132-140 for a typical attic is not out of place), the derating factor (multiplier) for 132-140 degrees is 0.71.

Back to the formula: 25 amps x 0.71 ambient derating = 17.17 amps x 0.7 derating for lack of spacing = 12.4 amp rating for that #14 AWG 90 degree C rated conductor.

That's ........ 12.4 amps rating ........ for that #14 AWG

Now for those in areas where it gets over 140 degrees in the attic ... 141-158 degree ambient derating factor is 0.58.

Back to the formula: 25 amps x 0.58 ambient derating = 14.5 amps x 0.7 derating for lack of spacing = 10.1 amps rating for that #14 AWG 90 degree C rated conductor.

That's ........ 10.1 amps rating ........ for that #14 AWG

Depending on the house there may be a #6 or a #10 in there for a 2nd floor dryer or an attic heat pump Aux-Heat circuit. In the example it was all 12's and 14's.


What I am hearing though is that although the IDEA of bundling is wrong the math says the safety margins make it a mute issue...Unless the wall cavity is going to get unrealistically hot... better to concentrate on making sure the wires are safe, not too many stuffed though too small holes in the plates, etc..



I have seen an attic at 160-deg, or at least the underside of the Roof deck read as that with my laser...I didn't go in and had to disclaim the attic as dangerous...

Bob,

Is Montgomery County not inspecting this houses?

What you showed in your pictures is nothing to be concerned about with bundling. You can add up all the figures you want. I am not sure (just based on those pictures) why there was so much responce to the post. I think folks just like playing with numbers.

If your pics are a concern the the rest of the homes on this planet should be condemed. That is about the slightest bundling concern I have seen (pictures) in years.

Originally Posted by Bob Sisson

What I am hearing though is that although the IDEA of bundling is wrong the math says the safety margins make it a mute issue...Unless the wall cavity is going to get unrealistically hot... better to concentrate on making sure the wires are safe, not too many stuffed though too small holes in the plates, etc..

The IDEA of bundling is wrong, and the math says ... well, what the math says depends on your location.

Such as:

I have seen an attic at 160-deg,

The IDEA of bundling is wrong all over, and the math says the same thing UNLESS you are located in an area where the attic does not get hot, OR, when the wiring DOES NOT GO through the attic.

In the case of your photos ... Houston, we have a problem ... not because of the bundling/lack of maintaining spacing IN THAT WALL, but because those same conductor ALSO go INTO THE ATTIC.

Take a two story house, *most likely* the NM cables, unless seriously bundled/lack of maintaining spacing is done (or spacing is not done), then there is no ambient derating *for the attic ambient temperature* to come into play, thus, derating for number of conductors would have to be for many NM cables.

Here is an example, let's say the electrician ran 20 NM cable all nice and neat (like they do where I seen them) along one side of the ceiling/floor system, not because it makes it nice and neat but because it makes running the NM cable simple.

That 20 NM cable will have at least 40 current carrying conductors, so, just to make sure we have the worst case scenario covered, lets add one more NM cable making the total number of current carrying conductors 42.

With 41 or more (does not matter how many more) current carrying conductors, the derating factor is 0.35.

Back to the formula: 25 amps x 0.35 = 8.75 amps without derating for any attic ambient. That is not good.

Okay, lets back down to 16 2-wire NM cables with 32 current carrying conductors. 31 to 40 current carrying conductors has a derating factor of 0.40: 25 amps x 0.4 = 10 amps without derating for any attic ambient. That is still not good.

Okay, let's drop back down to the next lower derating factor, for 11 2-wire NM cables with 22 current carrying conductors. 21 to 30 current carrying conductors has a derating factor of 0.45: 25 x 0.45 = 11.25 amps without derating for any attic ambient. That is still not good.

Okay, phew!, let's drop back down another derating factor, for 5 2-wire NM cables with 10 current carrying conductors. 10 to 20 current carrying conductors has a derating factor of 0.50: 25 x 0.5 = 12.5 amps without derating for any attic ambient. Well, what did you expect? 15 amps? Nope.

To say within the 15 amp rating of the breaker the number of 2-wire NM cables would need to be limited to 4, which would be 8 current carrying conductors, and 7-9 has a derating factor of 0.7, which would be okay as that would be 25 amps x 0.7 = 17.75 amps. No problem. OF COURSE, THOUGH, THERE IS NO DERATING FOR AMBIENT in there.

As soon as one or more of those NM cables goes up into the attic, that one or more NM cable would need to also be derated for ambient based on your attic temperature, and, as shown above, that is the real killer.

Think of it this way:

- 4 or fewer 2-wire NM cables which DO NOT go into the attic = NO PROBLEM.

- 3 or fewer 2-wire NM cables which DO go into the attic, after derating for a 132-140 degree attic (25 amps x 0.71 = 17.75 amps x 0.80 = 14.2 amps) = NO PROBLEM.

Bob,

It's not that they run up through the wall like that, it's that they continue on up into the attic which does it.

Yes, we should really be looking at it, as Ted should also. See the math above ... would you want a #14 AWG NM cable with a rating of 8.75 amps, even without derating for an attic, on a 15 amp breaker?

Now, take those typical lack of maintaining spacing bundles and put them in the attic (where I see them), that 8.75 amps now needs to be derated for ambient, 8.75 x 0.71 = 6.2 amps! On a 15 amp breaker!