stuffing electrical boxes

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Chris Lewis ( snipped-for-privacy@nortelnetworks.com) writes:

There's another puzzle for me. On an inside partition, The 3" box brings the incoming cable pretty close to the edge of the 3.5" stud -- closer than the 1.25 inch allowance, I believe. Where the cable is too close to the stud edge and not free to move aside, we're supposed to protect it against errant drywall screws using a metal plate attached to the stud. Would they be required behind the 3" box?
No wonder people hire electricians to do this. . .
-- "For it is only of the new one grows tired. Of the old one never tires." -- Kierkegaard, _Repetition_
James Owens, Ottawa, Canada
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On Mon, 4 Oct 2004 08:48:39 -0700, James Owens wrote

James -
I am not familiar with the code used in Ontario. Under the NEC, you would have to protect NM cable anywhere it was within 1 1/4" of the rough framing surface even "behind" a box. (I assume you're concerned with the side of the wall opposite to the box opening.)
To return to your original question: I'm surprised the Ontario code allows the box fill you're using. As another poster observed, it would not be allowed under the NEC, and I was under the impression that Canadian codes were generally more restrictive. More to the point: electrical codes are minimal requirements for safety. They are not design manuals. I never use single gang boxes (even the 2 1/2" deep ones) for duplex outlet installations. They just don't have enough room for wire and device installation. This is especially true with larger strap-mounted devices such as GFCI receptacles.
IMHO you should be using 4 x 4 x 1 1/2" boxes with 1/2" device rings (or thicker if your wall sheathing requires) for your application. Not only does the added space allow for easier installation, but it also allows for future expansion (adding another duplex, daisy-chaining another box, or whatever.)
By way of illustration, the NEC requires 2 cubic inches for each #14 conductor, with 1 conductor allowance for the aggregate of grounding conductors, 2 allowances for each strap-mounted device (such as a duplex receptacle), and 1 allowance for each internal cable clamp. Your application therefore involves 9 conductor allowances for 18 cubic inches. A 3 x 2 x 2 1/2 box is 12 1/2 cubic inches, while a 4 x 4 x 1 1/2 with 1/2" sindle device ring totals 24 1/2 cubic inches.
As far as cramming all those wires into the existing boxes, I can only suggest layering-in each set of conductors in a large flat loop against the back of the box, with the wirenut above or below the device. Then you're left with the device pigtails which have to be folded in accordion-like as you press the receptacle in. (A picture would be worth 1000 words...)
Again, I don't know what the Ontario code might say about how you've circuited the rooms, but under the NEC the only specifics for residential circuits involve special-purpose rooms such as bathrooms, laundry-rooms and kitchens/food-preparation areas. General-purpose receptacle circuits can be run any way you wish, provided the number of circuits is sufficient for the load and the load is approximately evenly divided among the circuits. (In the absence of any specific devices to be served, the load would be the 3 Volt-Ampere per square foot general lighting load.) There are requirements for the minimum number of receptacles, however. Basically, there must be an outlet for every 6 lineal feet of wall, with the outlets spaced as evenly as possible. You might check your code for a similar requirement...
Good Luck,
- Kenneth
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KJS wrote:

Is this really true that your have to protect the back of a 3" or 3.5" box for interior walls? I didn't see my builder do it 4 years ago when they built my house, that uses 2x4 studs. I don't think I see anyone do it .. I did not see anything like that at Home Depot.
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KJS ( snipped-for-privacy@sbcglobal.net) writes:

There are restrictions involving the receptacle size -- the tables I'm using assume are for receptacles or switches no deeper than one inch. For GFCI a bigger box would probably be required. Switches are a lot thinner than receptacles, but they're treated interchangeably.

The rule here is that any point on the wall has to be within six feet of a receptacle, measured along the wall (no cutting corners), with no obstacles (columns down to the floor, say). Also any isolated bit of wall longer than three feet has to have a receptacle. This is just for living spaces. The simplified code for kitchens takes up pages and pages. Thank goodness I don't need to know.
BTW, our figures are really in centimeters, but we just ignore that.
-- "For it is only of the new one grows tired. Of the old one never tires." -- Kierkegaard, _Repetition_
James Owens, Ottawa, Canada
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On Mon, 4 Oct 2004 11:57:27 -0700, James Owens wrote

James -
Thanks for the info. Glad you were already up to speed on the required receptacle (sorry, I meant point) spacing.
Regards,
- Kenneth
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A couple questions on this:
Does specifying the box size as 3 x 2 x 2.5 imply the box is metal? The OP spoke of grounding the box, so it is metal, I am just wondering about the terminology.
Why is a 3 x 2 x 2.5 metal box only 12.5 cubic inches? 3*2*2.5 = 15. Is the volume loss due to slight undersizing, or rounding the corners, or what?
In your conductor allowance, you made two allowances for clamps for the two cables. Do plastic romex clamps require an allowance? With metal clamps (two screws), can you put the clamp portion outside, and does that avoid an allowance?
Thanks, Wayne
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Wayne Whitney wrote:

I assumed a 3*3*2.5" box would be about 14 in3, but I looked it up and surprise: <http://doityourself.com/store/outletboxes.htm It is 12.5 for almost all of them.

You can completely remove the bottom clamp from a switch box and have both cables come in from the top and save one allowance. I've never tried moving a clamp to the outside of the box...
Bob
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On Mon, 4 Oct 2004 13:53:16 -0700, zxcvbob wrote

Wayne & Bob -
I was referring to metal boxes as covered by NEC 370-16. The table covers only certain common metal boxes. Other boxes (including plastic) must have their capacity indicated on them.
The trade sizes of boxes are the exterior measurements, and the cubic inch capacity is taken from the interior measurements. The difference is wall thickness.
The deduction for clamp fill applies to internal clamps only. Plastic or metal Romex clamps with an exterior clamping mechanism do not require a deduction. Not only can you install a "two-screw" metal Romex clamp with the mechanism outside the box, that's the way they're supposed to be installed! (The screws go outside and the locknut inside...)
Regards,
- Kenneth
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KJS wrote:

The clamps I was talking about are inside the box and have one kind-of big screw. One clamp covers 2 holes, and there's one clamp at the top and one at the bottom of the box.
Someone else asked about the integral clamps in plastic boxes (a little tab where you push through the cable.) I wouldn't count those at all, but I would make sure I wasn't already right at (or over) the number of conductors.
Bob
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It sounds like these are the only types of clamps that would count--internal metal clamps in a metal box. Or are there other examples of internal clamps? I've never added any clamp allowances in my calculations, and I want to be sure that I'm not supposed to.
On a semi-related note, if one uses an EMT conduit stub to protect NM cable that would otherwise be exposed to damage, is anything special (e.g. a bushing) required at the end of the conduit where the cable enters, or is it sufficient to deburr the conduit end?
Thanks, Wayne
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On Mon, 4 Oct 2004 15:21:04 -0700, Wayne Whitney wrote

Wayne -
Yes, those are the only type of clamp I've seen that requires a fill allowance. And, as Bob observed, you can and should remove unused ones.
Regarding sleeved NM: That would be up to the inspector (there is no specific code requirement), but IMHO, EMT would not require a bushing, just proper deburring as you suggest. However, Rigid or IMC used in that application would require one.
Regards,
- Kenneth
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Not only don't you count those, you can simply tear them out.
You don't need a clamp to enter NM cable into a plastic box, just a staple within 8" of the box. Many plastic boxes have no clamp at all.
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Here wrote:

I believe that only applies to single gang boxes.

FWIW, I've always seen them in double gang and bigger boxes, and never in single gang boxes.
Cheers, Wayne
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Not quite. While the code book may not make this clear, the 1.25 inch allowance is primarily for stud/joist/plate crossings. Because it's along the studs, joists and plates where you're going to fasten the wall covering, and where the fasteners will penetrate.
So, the wire sticking out of the bottom or top of a box isn't at risk from being hit with a drywall screw (unless the drywaller misses).
Yes, you could worry about screws for shelves and such not anchored in studs, but you're not likely to install one of those that close to a box.
Certainly, an inspector is going to prefer you stay away from the wall surface, but they won't in this case.
In my garage, the inspector said I could install the wires on the bottom of the roof trusses (because the ceiling was already insulated and vapor barriered), as long as I made sure I had 1.5" of clearance whenever the wire crossed ceiling lathe (where I'd fasten drywall). Virtually in contact with the drywall at other places - I wouldn't screw to the trusses, because there was a 3/4" gap from the lathe.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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Between studs, the wire will be pushed away from a drywall screw because it is not firmly attached at that point. Loosly attached, the wire deflects away rather than being pinned against a wire staple, or in a hole for a stud. However I read the 1.25" guideline as anywhere, whatever angle, including the rear of electical boxes, to the surface of the stud and the outer edge of immobilized wire. If a drywaller hits something with a 1 1/2" screw, he can protest that the other tradesman is the one at fault. Better safe practice for confidence later, I would use the metal plate behind those extra deep boxes. However if the circuit is planned carefully, you don't often need the extra-deep boxes.
Dave

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Owens) writes:
| Running a cable into and out of a box with a receptacle in it has got to be | a fairly routine thing -- practically unavoidable. You don't mean they require | 3.5 deep boxes in the States? (If so, they must be easier to stuff!)
The last time they tweaked the numbers I remember commenting to someone that the most common single-device configuration (cable "in", device, cable "out") now requires the deepest commonly available gang box. With #14 2+G cables that leaves one conductor allowance, I think. So you can make one or the other (but not both) cables 3+G. Anything more complicated and you have to go to multiple gang boxes or a square box plus mud ring. I never buy anything but the deepest boxes unless I have a special (particularly cramped) application.
                Dan Lanciani                 ddl@danlan.*com
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Since no one else has mentioned this, maybe I am doing it wrong, but I never use 8". 4-6" depending on what I am doing.
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In a previous article snipped-for-privacy@FreeNet.Carleton.CA (James Owens) writes:
:I've tried folding the wires accordion-style in advance of ;connecting the outlet and that helps a little, but I still feel like I'm :cramming the stuff in.
I don't like accordion folding because it flexes the wires at a few points and at sharp angles. I "cork-screw" the device into the box instead. The wires are bent continuously over the whole length, and tends to make it easier to push the device into the box.
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