Bundled MC

[EEC]

Do inspectors turn down installation of more than three MC cables bundled together? Such as home runs installed in drop ceiling going to the same area. cables are zip-tied together. Why does 310.15 (B)(2)(a) exception No 5 specify conductors to be number 12 awg? Why not 10 awg or 8 awg? What does exception number 5 mean by "Type MC cable without an overall outer jacket"?
PS sorry I should have put this in the NEC section

 

[George Stolz]

See 310.15(B)(2)(a), exception 5. MC cables on bridle rings are considered bundled.

However, that does not make it illegal - it just means you would have to derate the cables, and be sure that your ampacity is not less than the OCPD protecting it.

Off the record, , I would question how close together you were running those cables. Were they zip-tied together tightly, or did they simply run side by side?

 

[jjhoward]

How about modular homes that place plastic conduit in the walls for dropping in the bundles of wires from the attic to the basement?
I have seen that in 4 modular homes, and the inspector has yet to flag it.
The wire capacity (OCPD) has not been reduced. 12 awg wires all had 20 amp breakers in the breaker pane.

 

[infinity]

There is an exception that allows up to 20 #12 AWG CCC's bundled together to be derated to 60%. For 20 CCC's this would work to a derated ampacity of 18 amps (30amps X 60%) so these circuits could be protected by a 20 amp CB. You just have to be careful when applying the provisions of 240.4(B). Multi-receptacle circuits can not be rounded up to the next higher standard OCPD device.

 

[EEC]

12 awg MC cable

12 awg MC cable

See 310.15(B)(2)(a), exception 5. MC cables on bridle rings are considered bundled.

However, that does not make it illegal - it just means you would have to derate the cables, and be sure that your ampacity is not less than the OCPD protecting it.

Off the record, , I would question how close together you were running those cables. Were they zip-tied together tightly, or did they simply run side by side?

Why does exception No 5 specify conductors to be number 12 awg? Why not 10 awg or 8 awg? What does exception number 5 mean by "Type MC cable without an overall outer jacket"?

 

[jjhoward]

These 20 amp circuits were all general purpose lighting/power circuits. Seems like they should be derated.

 

[GUNNING]

Its that 5 degree Celsius rise in temperature from all those wires being bundled together. It just ruins all those screws on those switches and outlets and breakers. I wonder what the engineers would do if they found out about the 100 degree Celsius summer temperatures in attics all across the country. Shshshsh. I guess that would be 205 degrees if the wires were bundled more than 5 together. I hope the copper industry doesn't here about this or they will have us run 8-2 w/ grds for 20 amp circuits, in conduit.

Imagine the lugs on that light switch! Imagine the BOX!