derating or not nm

Status
Not open for further replies.
K

keenalu1

Banned
Location
Northwest
I have 2(12-2) and 3(14-2) in a 1 1/8 bored hole through three top plates (4 inches in total); now the inspector or the person whom believes himself to be the (AHJ) has sited article 310.15. I think to myself "what a moron, Am I missing something!
 
Bundling would only apply if the bundle were more than 24". The OP said 4" total. Bundling would not apply to this installation.
 
He may be correct (depending on interpretation of the following code quote) but citing the wrong article, see 334.80.

334.80 Ampacity
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.

Where more than two NM cables containing two or more current-carrying conductorsare bundled together and pass through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).
Click to expand...

I think this poorly worded but can see where it could be cited if the top plate is to be fire- or draft-stopped

Roger
 
Roger is correct, but the OP never mentioned firestopping. Besides that, 310.15(2)exception just about nullifies any derating for NM cables through a firestopped hole. If I remember correctly someone had made a proposal for the 2008 NEC to delete the second paragraph of 334.80. Might have been Ryan.
 
Most of my installs are not inspected. I have thought about this issue many times because sometimes I add that extra wire. I consider the load of wire at that point, if I have a switch leg and two power wires that don't have much load I put them all through the same hole. I would hesitate to put four wires through a hole that were heavy loaded, but it would probably never be a problem.
 
-marty said:
...if I have a switch leg and two power wires that don't have much load I put them all through the same hole. .
Click to expand...

I didn't know the code differenciated between the degree of what constitutes a current carrying conductor and what doesn't.
 
celtic said:
-marty said:
...if I have a switch leg and two power wires that don't have much load I put them all through the same hole. .
Click to expand...

I didn't know the code differenciated between the degree of what constitutes a current carrying conductor and what doesn't.
Click to expand...



This has come up before regarding travelers for 3-way switches. Do they or don't they both count since only one is a CCC at any given time.
 
additional info

additional info

yes in fact it was fire insulated and there were two HR's , 1 SL, and 2 jumpers, we all know as a standard practice to load calc at 80%. I drilled an additional hole and also left this for him:

http://www.cbs.state.or.us/external/bcd/pub/tricounty/newsflash/winter_05.pdf

this is my state chief inspectors interpretation

i had to go to work for a few hours this morning and am apologize for not getting back to you all till now.

thnx for the input
 
infinity said:
If I remember correctly someone had made a proposal for the 2008 NEC to delete the second paragraph of 334.80. Might have been Ryan.
Click to expand...
It was.
7-71 Log #1344 NEC-P07 Action: Reject
(334.80)
_______________________________________________________________________________________________
Submitter: Mike Holt, Mike Holt Enterprises
Panel Meeting Action: Reject
Panel Statement: Technical substantiation submitted during the 2005 Code cycle supported the addition of the second paragraph in 334.80. While the cable is only bundled for a short distance within the fire- or draft-stopped wood framing, it is long enough that the insulated conductors exceed their allowable temperature rating.
Click to expand...
On the proposal prior, they accepted text that excludes using the exception in 310.15:
7-70 Log #880 NEC-P07 Action: Accept in Part
(334.80)
_______________________________________________________________________________________________
Submitter: Noel Williams, Noel Williams Consulting
Panel Meeting Action: Accept in Part
The panel accepts the addition of the phrase ?and the provisions of 310.15(A)(2), Exception, shall not apply?.
Click to expand...

infinity said:
This has come up before regarding travelers for 3-way switches. Do they or don't they both count since only one is a CCC at any given time.
Click to expand...
I submitted a proposal for 2008 to exclude a traveller from derating. It was rejected on the premise that the 2005 already allows a traveller to be excluded, 310.15(B)(2).
6-50 Log #1405 NEC-P06 Action: Reject
(310.15(B)(2)(a), Exception No. 6 (New))
_______________________________________________________________________________________________
Submitter: George Stolz, II Pierce, CO
Panel Meeting Action: Reject
Panel Statement: The proposed exception is not necessary. The present language of 310.15(B)(2) already permits what the submitter is proposing.
Click to expand...
 
It's funny George, when I read 310.15(B)(2) I don't see that existing language in the 2005 NEC. I think that your proposal was a good pretty good one since it was explicit in it's intent.
 
This has come up before. There is no requirement to derate for your application. Even if you have to derate its not a problem as you are derating from the 90 Deg C ratino, IE 25 amps for 14-2 NMB.
This may of been required for NM prior to 1984
 
tom baker said:
This has come up before. There is no requirement to derate for your application.
Click to expand...
What is the reason that 334.80 doesn't apply to require the derating ?
tom baker said:
Even if you have to derate its not a problem as you are derating from the 90 Deg C ratino, IE 25 amps for 14-2 NMB.
This may of been required for NM prior to 1984
Click to expand...
Actually he does have a problem because the 25a for 14-2 and 30a for 12-2 get adjusted down to 12.5a for 14-2 and 15a for 12-2 when you hit that 10-20 conductor category in Table 310.15(B)(2)(a). The 2(12-2) and 3(14-2) total out to 10 curent carrying conductors.

If there were only 9 total cc conductors, it would be 70% ampacity which would be 17.5a for the 14-2 and 21a for the 12-2.

He's one over the limit.

David
 
dnem said:
tom baker said:
This has come up before. There is no requirement to derate for your application.
Click to expand...
What is the reason that 334.80 doesn't apply to require the derating ?
tom baker said:
Even if you have to derate its not a problem as you are derating from the 90 Deg C ratino, IE 25 amps for 14-2 NMB.
This may of been required for NM prior to 1984
Click to expand...
Actually he does have a problem because the 25a for 14-2 and 30a for 12-2 get adjusted down to 12.5a for 14-2 and 15a for 12-2 when you hit that 10-20 conductor category in Table 310.15(B)(2)(a). The 2(12-2) and 3(14-2) total out to 10 curent carrying conductors.

If there were only 9 total cc conductors, it would be 70% ampacity which would be 17.5a for the 14-2 and 21a for the 12-2.

He's one over the limit.

David
Click to expand...

He would only have a problem if the 310.15(B)(2) exception did not apply.
 
Why was it firestopped in the first place? Is this a dwelling or some other occupancy? 3rd question is "who is the knucklehead who went around sticking thermometers in firestopped top plates with more than two cables in them in the first place? Didn't he have anything better to do?
 
Status
Not open for further replies.
Top