Re: 3-way switch loops
Originally posted by jwelectric:
Larry
Being that you brought it up would not most cables coming from a multi gain box be on the same circuit?
How should this be looked at as to bundling ?
Here's what I meant: let's suppose we have a 4-gang switchbox at the door of a good-sized bedroom for, oh let's say, a ceiling fan/light combo, a pair of recessed lights, and split-wired receptacles. That's four switches, but let's calculate box fill, using #14 conductors:
The fan/light takes a 14/3, the receptacles a 14/3, the recessed lights a 14/2, and feed-in and feed-out are also 14/2's. That's a total of 12 current-carrying, plus 1 for grounds, 8 for 4 devices, and one more for clamps. Total: 22; at 2 cu.in./conductor, that requires 44 cu.in.
A 4-gang Carlon nail-on has a 55-cu.in. capacity, so we're okay there. But what about the wires running up and/or down in the wall? If they all go up, that's a bundle of 12 conductors, which should be derated, right?
However, if they're all on one cicruit, the agregate heat build-up shouldn't exceed that of a single cable. The total current should never exceed that of the circuit's rating, even though the box is relatively full, especially if dimmers are used.
Now, let's say we have three separate circuits feeding three switches in a 3-gang nail-on, each circuit having a feed-in hot and neutral, and leg-out hot and neutral. Total conductors: 12, as above, plus grounds, devices, and clamps. However, we have 3 circuit's potential of total load current.
That requires a box of 40 cu.in. The Carlon 3-gang nail-on is 44. We're okay here again. Note that we once again have 12 conductors running up the wall. However, this time, we have three circuits, each contributing their share of heat build-up.
In the first example, I wouldn't hesitate to bundle or stack the cables together, and even use one or two bored holes, although an inspector might have an issue with it. In the second example, I would definitely separate the wires more, maybe two stackers, and bore three holes.
My point is that there's bundling, and then there's bundling. The maximum expected, or possible, total current load is as important as the sheer quantity of conductors when it comes to cable bundling and box fill, as far as real-world performance is concerned.
