"jagerEd" wrote in message
t...
The Web site:

http://www.hometime.com/Howto/projec...elec_4.htm#box


gives the following rules for sizing an electrical box:

1. Count the number of wires for the box. Don't count outlet/switch
pigtails
and count all ground wires as one.

2. Take that number, add one for each cable clamp, and two for each device
(like a switch or outlet).

3. If the box contains only 14-gauge wires,
multiply the total by 2 cubic inches.
Or, for 12-gauge wires, multiply the total by 2.25 cubic inches.

The result is the minimum allowable volume the box should be.
Volumes are usually stamped into the back of the box on the inside.

I'm not clear on exactly what is meant by "Don't count outlet/switch
pigtails."
My guess is it means that when several wires are twisted together they
count
as only a single wire.
Is that right?


What it means is that a conductor, no part of which leaves the box (such as
a pigtail), is not counted.


So, suppose I hav a box with switches and 4 (aluminum wire, #12) cables
attached. I know that
one of the cables is the LINE, and two go to lights in the room with the
box. I presume the fourth cable goes off to
another lighting load somewhere else in the house. So here's my count:

1. It looks like the whites are all twisted together, giving a count of 1


No, each white wire leaving the box is a count of one, for a total of 4.


2. The grounds are all twisted together, giving a count of 1.


Correct, the total of all the equipment grounding wires only count as one.


3. The LINE black is twisted with 3 other blacks, 2 going to switches and
one, I think, going to the other load. Count 1
4. The blacks in the 2 cables going to lighting fixtures each count as 1,
giving a count of 2.
5. The 2 switches give a count of 4


The four black wires leaving the box count as one each, for a total of 4.
The pigtails to the switches do not leave the box, so are not counted.


6. No cable clamps, as these are plastic boxes.

Total: 9


Count 4 for the white wires
Count 4 for the black wires
Count 1 for the equipment grounding wires
Count 4 for the devices ( 2 switches on separate yolks)
________________________

Total count: 13



Since these are #12, the minimum box size is 2.25 x 9 = 20.25 cu. in.
The box measures 2.5 x 2.75 x 3.5 = 24.1 cu. in.


(2.25cu. in.) x 13 = 29.25 cu. in.


The point of all this is can I put one more cable in there to serve a new
lighting load in the room,
controlled in a separate switch box? It would seem so, because the count
does not change at all,


No, the box is already over allowance. Adding another cable (#12) would add
another 2 count (one black, one white) or 2.25 x 2 = 4.5 cu. in. for a total
of 33.75 cu. in. box needed.


if I'm doing it right. Nonetheless, it seems awfully crowded in there.

TIA for you insights.

Ed