# Cheat sheet for bored holes



## mikedl361 (Dec 24, 2016)

Anyone know where I can look up and find a cheat sheet on how many NM cables you can run through various size bored holes when running romex. Mainly referring to 12/2. All replies appreciated .


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## Bird dog (Oct 27, 2015)

Depending on where the holes are, it might be a mute point once you derate.


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## joebanana (Dec 21, 2010)

The code doesn't directly address how many NM can be run through a bored hole. So, as many as can be installed without damage. As for derating, I would think the 24" or shorter sleeve requirement would apply.


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## frenchelectrican (Mar 15, 2007)

mikedl361 said:


> Anyone know where I can look up and find a cheat sheet on how many NM cables you can run through various size bored holes when running romex. Mainly referring to 12/2. All replies appreciated .


The answer will varies a bit. 

It depending on what and where ya bore it thru.


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## mikedl361 (Dec 24, 2016)

joebanana said:


> The code doesn't directly address how many NM can be run through a bored hole. So, as many as can be installed without damage. As for derating, I would think the 24" or shorter sleeve requirement would apply.


I thought I read somewhere, for example, if you have a 1" hole you can pass (3)12/2 romex and 3/4" would be 2. Was that wrong.


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## canbug (Dec 31, 2015)

Pull some wire and you'll know just by looking. If you overfill just because they fit, the wire will tell you really quick. Give yourself some space and drill an extra hole when you need it.

Tim.


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## GeneC (Aug 28, 2017)

what are various sized holes and where are they it depends on a few factors. Are you talking through joists.


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## WIsparky71 (Mar 7, 2015)

If they are in contact with insulation there is a de-rating formula. It basically comes out to 8 current carrying conductors per hole. If there is no insulation, I think you can pack them as full as you want, not that that's always a good idea. 

Sent from my XT1080 using Tapatalk


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## lighterup (Jun 14, 2013)

here ...it's a local thing . One county does not
allow it , the next county will say 3/4" hole
can have (2) 2 wire NM if they are both 120 volt.


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## Arrow3030 (Mar 12, 2014)

I've never heard of a table for it.
2 per 3/4" hole is my standard. Unless of course the drills already put away and it's a short run.
12-2-2 or 14-2-2 gets it's own hole. I only use that if it's already on site though.


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## electricguy (Mar 22, 2007)

For some reason I drill my holes at 7/8ths damn ship arbors are now 55.00 for a greenlee nail biter 18 inch


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## chicken steve (Mar 22, 2011)

Arrow3030 said:


> I've never heard of a table for it.
> .


This is what i have for foam>>> 


*334.80*>
Where more than two NM cables containing two or 
more current-carrying conductors are installed, without 
maintaining spacing betwecn the cables, through the same 
opening in wood framing that is to be sealed with thermal 
insulation, caulk, or sealing foam, the allowable ampacity 
of each conductor shall be adjusted in accordance with 
table 310.15(B)(3)(a) and the provisions of 310.15(A)(2), 
Exception, shall not apply. ***

Where more than two NM cables containing two or 
more current-carrying conductors are installed in contact 
with thermal insulation without maintaining spacing be-
tween cables, the allowable ampacity of each conductor 
shall be adjusted in accordance with Table 310.15(B)(3)(a).


<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>

*310.15(B)(3)(a) Adjustment Factors.* 
(a) More Than Three Current-Carrying Conductors. 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 spacining 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)(3)(a). 



<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>



*310.15(A)(2) Exception*: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit 
length figured at the higher ampacity, whichever is less. 


~CS~


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## btharmy2 (Mar 11, 2017)

Why would it be necessary to derate for wires running through a hole in a 1-1/2" thick piece of wood when you don't need to derate wires through a 23" long conduit sleve????


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## Arrow3030 (Mar 12, 2014)

^thermal insulation


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## chicken steve (Mar 22, 2011)

If we spray foam 14-4 in a wall, T310.15(B)(3)(a) 4-6+80% of T310.16'2 25Amps which is 20Amps. 

fused @ 15A

It's been argued that i can only use the tables, not the article for thermal foam in the past

which i disagree with

~CS~


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