Adding switch/light to existing circuit

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Old 06-17-09, 08:42 AM
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Adding switch/light to existing circuit

I have a room with a ceiling light controlled with a on/off switch. There is a black/white/grd from breaker to switch and black/white/grd from switch to light.
I would like to add another light controlled with a separate switch. I would like the switches side by side, probably in a double elec box. As I understand I can't have 2 wires under the same terminal screw on the switch. Do I need to run new power wires from the breaker to the new switch?
SteveS
 
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Old 06-17-09, 09:01 AM
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As I understand I can't have 2 wires under the same terminal screw on the switch. Do I need to run new power wires from the breaker to the new switch?
SteveS
No, just pigtail. That is connect two 6" long pieces of wire (pigtails) to the incoming power wire. Then hook one pigtail to each switch. In this case the white from the new cable would go to the existing bundle of whites. Use #14 NM-b (Romex) for a 15a breaker. #12 for a 20 amp breaker. Shut off power at breaker before doing any work.

If you use a duplex switch you won't need a double box but a double box is easier to work in. If you use a duplex switch you will not need the pigtails.
 
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Old 06-17-09, 03:46 PM
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I'd like to stay with 2 reg switches for appearance sake. However, that's alot of #12 pigtails to cram inside that box. The box is 32ci & says 14of#12. How many wires can I have in there with 2 switches?

OR I was also thinking of using a duplex switch, turning the box 90deg, and using half the box as a junction box. At least the 2 toggles would be vertical. Would that work as long as the stud isn't in the way of the tabs on the box?
SteveS
 
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Old 06-17-09, 05:28 PM
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I'd like to stay with 2 reg switches for appearance sake. However, that's alot of #12 pigtails to cram inside that box. The box is 32ci & says 14of#12. How many wires can I have in there with 2 switches?
You are talking about a standard double gang box aren't you? The setup I described is a common one for two switches in a double gang box.
OR I was also thinking of using a duplex switch, turning the box 90deg, and using half the box as a junction box. At least the 2 toggles would be vertical. Would that work as long as the stud isn't in the way of the tabs on the box?
It would not be an NEC violation. Appearance is a matter of taste though. I'd find it strange. If you have a double box just use two switches. That is one of the reasons they make double gang boxes.

Here is how to figure box fill. Note pigtails don't count.
Here's how to figure the size box that complies with the NEC.
Step one

Add up the wires and devices, A K A "conductor equivalents" (wires that start and end in the box -- pigtails -- aren't counted)

Each current-carrying wire = 1
All ground wires together = 1
All clamps together = 1
Each receptacle or switch = 2
Step two

Multiply the number of conductor equivalents (total from step one) by their volume factor in cubic inches (listed below)

14-ga. wire takes 2 cu. in. per conductor
12-ga. wire takes 2.25 cu. in. per conductor
10-ga. wire takes 2.5 cu. in. per conductor
If a box contains different gauges of wire, use actual volume factors for the wires and the largest volume factor for ground wires, devices, and clamps.

Example

A PVC box has two 14/2 cables, one 14/3 cable, and one receptacle. The box has no internal clamps. What's the minimum box volume needed?

Step 1. Count the conductors:
2 conductors per 14/2 cable x 2 cables = 4
3 conductors in the 14/3 cable = 3
All grounds together = 1
No internal clamps = 0
Receptacle outlet = 2
Total conductor equivalents = 10

Step 2. The volume factor for 14-ga. wire is 2 cu. in., so:

10 conductor equivalents
x 2 cu. in.
= 20 cu. in. box

Source: More Wires Need Bigger Boxes - Fine Homebuilding Article
 
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Old 06-17-09, 05:50 PM
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Using your example you would have 3 2 conductor cables and 2 switches in a 2 gang box.

3x2 = 6
2 switches = 4
1 ground
Total 11 conductor counts. 11x2 =22 cubic inches for 14 gauge wire.

11x 2.25 = 24.75 cubic inches.

Most 2 gang boxes are around 32-34 cubic inches.
 
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