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Reading book on electrical work: think It's wrong-want to check.

Reading book on electrical work: think It's wrong-want to check.


Old 05-08-17, 08:05 PM
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Reading book on electrical work: think It's wrong-want to check.

I have the "Black & Decker" "The Complete Guide to Wiring" and on page 63, there is a photo of an electrical box (a plastic one) and underneath is a caption that says this exactly: "Boxes larger than 2 x 4" and all retrofit boxes must have internal cable clamps. After installing cables in the box, tighten the cable clamps over the cables so they are gripped firmly, but not so tightly that the cable sheathing is crushed."

I don't see how the first line can possibly be true. ALL of the retrofit boxes I have seen have those plastic grippy parts, and no metal cable clamps. Even with metal boxes, it seems external clamps would pretty much always be better and preferable to internal clamps (for space reasons alone).

The book is not new, but not terribly old either. But I can't imagine a time when the above caption from the book would have ever been a true statement.

So, I just wanted to check, since I'm certainly no expert. But when I'm doing jobs with 4 11/16 boxes, it's okay to use external hole-mounted clamps, right? I can't see why those would not be allowed just because my box is bigger than 4x4.
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Old 05-08-17, 08:28 PM
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You're confusing cut-in gem wall boxes with splice boxes.

Single gang plastic wall boxes usually have breakout tabs.
Two gang and larger have clamps.

Those plastic grippy things actually hold pretty well. Those clamps are usually molded in the closed position. Use a flat heat screwdriver to break the one side free but leave the hinge side intact. You need just to start the clamp open. Pushing the cable thru the clamp will force its way in and become captive.

With 4" and 4-11/16" boxes you need actual NM connectors... be they the metal type with a locknut and two screws or the snap-in plastic type.
Old 05-09-17, 08:16 AM
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The push-in plastic grippy inserts count as cable clamps. They don't have to be metal or adjustable to meet code.
Old 05-09-17, 08:55 AM
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The wording in the book is confusing and wrong. The rule does not require internal clamps, just that cables need to be secured to the box with a few exceptions. One exception that I think they are trying to point out is that a standard single gang plastic box doesn't need an NM or UF cable secured to it if stapled within 8" of the outside. The clamps/knockouts are broken out and can still pass inspection. 2 gang and larger blue boxes you do not break out the tabs but need to clamp as described by PJ.

Installing an old work (retrofit) metal box with external clamps can be difficult so internal clamps would be recommended but is not required.
Old 05-11-17, 10:53 AM
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Perfect information. Just what I was hoping to hear.
I appreciate all the responses.

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