Greeting all,

When calculating the size of a box needed, how do you calculate special feature devices, as in timers, dimmers, fan, in terms of cu. inch used?

Are the cubic inch dimensions required on the device or do you whip out a pencil, with large eraser and go back to ninth grade, or earlier?

I've heard of some new fang-led toys called calculators but they were forbidden by both Dominican Nuns and Irish Christian Brothers. Go figure!

Much to my disagreement, a device is a device. ANY device counts as two of the largest conductors in the box. Same goes for the grounds. They all get counted as one conductor based on the largest on the box.
I say disagreement because I think a GFI, dimmer, timer, etc, should count for more than a small SP switch.

So let's say you have a non-metallic three gang box in a bathroom. There is one 12/2 for the receptacle circuit and several 14/2's for the lighting and fan. You would deduct 6.75cu/in for the three devices and another 2.25cu/in for ALL the grounds.

I agree they should count as more, I do a lot of Automation, I use Extension Rings at Most switch locations to provide room for controls, They usually want later(after walls are up).
I agree with Stanforty, except I would just run the 12-2 directly to receptacle and not go through switch box.

Just to let you know about my example here. I meant having the GFI receptacle IN the 3-gang with the switches. I do this sometimes in a small or half bath to save wall space ro if space is tight.
I wasn't implying that the 12/2 passed through the box to another.

I do a lot of Automation

Which manufacture are you or the company you work for using?