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Sizing electrical wall boxes.
"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 |
#2
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Sizing electrical wall boxes.
On Fri, 04 Jul 2003 23:28:28 GMT, "jagerEd"
wrote: 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? No, the mean wires coming from a switch or outet connected to the bunch of wires. 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 2. The grounds are all twisted together, giving a count of 1. 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 6. No cable clamps, as these are plastic boxes. Total: 9 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. 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, if I'm doing it right. Nonetheless, it seems awfully crowded in there. TIA for you insights. Ed |
#3
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Sizing electrical wall boxes.
You can
1) replace the box with a bigger box (pretty ugly job) 2) Intercept the cable you want to feed the circuit before it gets to the box or after it leaves the box or whatever it may do, cut it, put the long end into a new box and splice it to a new cable running to the old box; also take off a cable for your new light load. All this assumes that the circuit you are using isn't already got a lot of load; there certainly is a lot of stuff in the box. As was pointed out, the box is overfull, suggesting that some of the stuff there was added after inspection. 3) Find another source for power, i.e. a box which isn't so full. If you are daunted by all this, it might be a good idea to talk to an electrician. The fact that you have #12 aluminum wiring in the box and are going to have to splice in copper is another complication. "jagerEd" wrote in message news Volts, So, what is the way forward here? What do I do? there must be SOME way I can do this. "volts500" wrote in message m... 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. |
#4
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Sizing electrical wall boxes.
You will need to replace the box if you want to add additional conductors.
Volts, So, what is the way forward here? What do I do? there must be SOME way I can do this. "volts500" wrote in message m... 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. |
#5
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Sizing electrical wall boxes.
"jagerEd" wrote in message t... Thanks, Donald. Your list seems to have all the options, none of them really good. Here's the problem I see with each: 1. I would be willing to replace the box with a bigger one if I can find one. But the one that's in there is circa late 60s brown plastic, is basically the same internal size as the steel, gangable old work box with sections. I will go to the Arrow Hardware and HD today and look again, but do not recall having seen a deeper box. Do they exist? 2. Your "cut & splice" alternative is a good one except for lack of available length. I can see into the wall there because I (boldly) cut the plaster for the new 2-gang box, just a few inches from the existing one. The "load" line MIGHT be long enough to swing over the the new box, but it would be tight. If it didn't work, I'd be in trouble. 3. Finding a new power source is possible but not attractive. I'd have to find the "end" of the lighting circuit, by peering into switch boxes or tracing cables in the attic, then fish a new cable up and pull it down into the bathroom getting the new box. I just did some of that to go from the new switch box to the new exhaust fan and new light, so I know how but it's not fun. Worth thinkig about nonetheless. BTW, the existing box is original. We have lived here since 1972 and the house was built in 1968, with a single previous owner. By comparing this box to others I've had occassion to work on in the house over the years it's clear no changes have been made. And, it's a tract house, so it's hard to believe the inspectors didn't approve it in 1968. And, it's really not that complicated is it, 2 switches in a box mid-way along a lighting circuit? Thanks again for clarifying matters for me. I first option will be looking bor a bigger old work 2-position box. Ed You can use a 4 11/16" square x 2 1/8" deep box (metal, 42 cu. in.) with a 2 gang 4 11/16" plaster ring. You can attach the box to the stud with drywall screws through the holes in the side of the box. Don't forget to ground the box by connecting the equipment grounding conductor with a green ground screw to the box. I'd be concerned about splicing copper to aluminum though.....special connectors are needed. Also, if the feed is for a receptacle in a bathroom it should have it's own circuit. |
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