Bundling 12/2 mc in cable tray.

[BlazeMoody]

There seems to be a lot of debate and confusion over NEC code 310.15(B)(2)(a), especially exception 5...
I have a guy who just put approx 150 12/2 mc cables, and some even larger, in a wire cable tray, without any spacing. Is this legal? The way I read it is that, because there's 300 ccc (1 hot+neutral), it exceeds the 20 ccc rule, therefore meaning he must derate, correct?

https://m.facebook.com/groups/237138492156724/permalink/354690620401510/?sfnsn=mo&mibextid=mMAx51

 

[dm9289]

310.15B(3)(4) exception.
“IF”they were all #12 a 60% adjustment factor applies 30 amp @60%=18amps next size up breaker 20 amp.

But also you may want to look at 392.80 for cable trays various situations there.

 

[infinity]

Regarding (310.15(C)(1)(d) 2020 NEC) this section allows you to bundle up to 20 CCC's before you need to apply any derating but that exception only applies to #12 conductors. Once you add in conductors of other sizes then the exception seemingly cannot be used. Furthermore when using the exception you can apply a derating factor of 60% so for #12 AWG cables, as dm stated you end up with a conductor ampacity of 18 amps. If any of the these #12 MC cables are for multi-receptacle (not individual branch circuits) then you cannot use the next size up rule so you'll end up only 15 amp circuits.