This will probably be long winded but thanks for the patience. I have been told I cannot run more that 3 wires through tgi's in the same hole due to de-rating. I've also been told I can run more than 3 in the same bored hole. I'm confused. I understand the not more than 3 as far as a raceway is concerned but again, confused. We dont have to de-rate anything 2' and below, since that is considered a nipple. Are 5/8" holes every 12 inches considered to be nipples or are they considered to be a free air raceway since the cables travel with each other over multiple feet? A little scatter brained question I know, but that's how it is bouncing around in my head. Sorry.
Electrical Code Academy, Inc.
~100% Online Electrical Educational Programs~
Greetings Fella - the issue you are referring to happens to be covered in 310.15(B)(3)(a): "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)(3)(a)." Now, if you run them through bored holes that do not contain insulation, foam and so on then you only have to determine if the cables are in deed bundled. The fact they are through bored holes at close proximity lend them to being considered bundled unless you physically space the cables in the locations between the joists. Now, if considered bundled you would have to consider that once you get past 3 current-carrying conductors you have to apply adjustments. So even with 12/2 NM-B for example you could "bundle" (4) 12-2 NM-B and as long as you don't exceed 9 current-carrying conductors then even after the adjustment you would be fine. As for how many cables you can stick in a bored hole the answer is as many as you can without damaging the cable....BUT again once you get past 9 current carrying conductors (each 12-2 is counted as 2 current carrying conductors) you will have a problem. Now, you throw insulation into the cavity and more than two NM-B is in contact with it the 310.15(B)(3)(a) applies. You fill those bored holes with Foam, Caulk, or insulation and put more than two NM-B cables in the hole then you also apply 310.15(B)(3)(a).
Awesome. Thanks for getting back to me so quickly Paul. So, how close do the cables need to be to he considered a "bundle"? I'm just trying to thoroughly understand the code so that it makes sense. Also, side question, is there an apprentice program you offer or is it the individual courses you offer?
I recommend our Residential Program as it covers these items and more. Its an amazing program. As for bundled...its not defined but if they are less than a 3/4" from each other then thats always been my rule of thumb but will vary with inspector. Pull them apart in the space between joists kinda breaks up that bundle.