Wiring a three gang box

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Old 02-17-13, 07:58 AM
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Wiring a three gang box

I am rewiring my upstairs. My questions are about wiring of a plastic three gang box. The box will have three three-way switches.
Two 20 amp circuits will come into the box (each a 12/2 w G). The first circuit will have three lines coming out of the box. One to the dining room (12/2 w G), one to the kitchen sink light (12/2 w G), and one to the other three-way switch for the kitchen recessed lights (12/3 w G). The second circuit will have three lines coming out of the box. One to the laundry room lights, bathroom lights, and living room ceiling fan (12/2 w G), one to the other three-way switch for the first half of the living room recessed lights (12/3 w G), and one to the other three-way switch for the second half of the living room recessed lights (12/3 w G). That is two 12/2 w G going into the box, three 12/2 w G going out of the box, and three 12/3 w G going out of the box. Written in the box is 61.0 CU. IN. and 27 #12.
1. Is it OK to have two circuits in the same box?
2. Is this many wires and switches OK for this box?
3. Do I tie all the grounds together with a pigtail for each switch or do I keep the grounds for each circuit separate?
4. For rough-in do I do all the in-box splicing just having loose wires for the three three-way switches?
5. Any recommendations or observations?
 
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Old 02-17-13, 08:34 AM
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Designate by switch which lighting they will control. Obviously you won't have a switch operating the laundry room, bathroom and living room fan. Why are you bringing all that wiring into the switch box when most of it will not be switched at that location?
 
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Old 02-17-13, 10:21 AM
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Why are you using #12 wiring for lighting. It takes up a lot more space in the boxes and it is not required on lighting circuits.

It is ok to have two circuits in one box.
In the same box.... all grounds get tied together with pigtails left out to the devices.
It is far better to make up all your connections now when the wiring is installed while the circuits are fresh in your mind.

It is a good idea to twist the wires for a particular device. Twist the two wires for a two pole switch. For a three way switch......twist the two travelers together and then wrap the common with it.

Do as much as you can now because later when you put the devices in you'll have forgotten what you did.
 
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Old 02-17-13, 10:50 AM
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I didn't do the math but you can calculate the box fill.

Regardless, that sounds like a LOT of 12 AWG solid wire to manipulate in the box along with three three-way switches. When you figure on folding 6" pigtails in there, I predict a rat's nest.

Another factor is that a plastic box may deform if you try to force things in, which makes screwing in the switches an exercise in frustration. If the calculations work out, I would at least put in the largest box that would look reasonable, and if it was a tight squeeze, I'd use a metal box. If you had a 4-gang, maybe you could just put a blank on the end.

I used 12 AWG for all circuits in the entire house because I bought 500' rolls of stranded and it was easier and cheaper than buying both 14 and 12 AWG, and I figured I'd just use all 20A breakers except as required. But, 12 solid is a lot harder to work with and residential plastic boxes are more oriented toward 14.

Diagram what's going in and out based on the KOs in the box and "dry fit" the switches in the actual box to see how much room you've got left for your pigtails. Have you considered putting a 4-11/16 box somewhere concealed, like in a closet, that you could use as a j-box, and then just run switch loops into the 3-gang?

For RI inspection it's typical to just coil wires inside the box. That's what I did.
 
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Old 02-17-13, 07:00 PM
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I only had two 12/2 w G going into the box. Everything else was going out. It was the first box that those two circuits were going into. I like the idea of running those two circuits into a junction box first. I can put the junction box in the laundry room which is on the other side of the wall from the three gang box. The panel box is in the laundry room. I can limit the wiring in the three gang box to two 12/2 w G in and three 12/3 w G out. The reason for using #12 wire is the number of recessed lights. I am using 21 H7ICAT cans which can take up to 150 watt bulbs. I will probably be using 13 watt compact flourescent bulbs in the cans. It doesn't take many 150 watt cans to use up 80% of 20 amps. I ended up needing three lighting circuits for my 883 sq.ft. upstairts. Thanks for answering all the questions and thanks for the good suggestions. I will do all I can during rough-in and leave as little to memory as I can. Any more recommendations are sure welcome.
 
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Old 02-17-13, 07:17 PM
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You do not need to limit the circuits to 80% unless you are planning everything to be one for 3 hours or more.
 
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Old 02-17-13, 09:23 PM
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H7ICAT cans which can take up to 150 watt bulbs.
I'm not sure if you can find a reflector bulb that big.....even 120 watt is almost extinct.
 
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