Securing wires in junction boxes

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  #1  
Old 06-25-02, 09:27 AM
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kpell
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Securing wires in junction boxes

Just one question about securing wires in plastic junction boxes, I have installed the plastic boxes and ran the wires up to the junction boxes, my dilemma is that I was told by a local that if you used normal nm connectors(metal cable clamps) that fit into the box with a locknut on the back that I would have to ground them someway, even if I used a plastic box. I don't see any way of grounding the clamps. Is this true? Does code allow plastic boxes and metal clamps? If not what then? I have yet to find any other type of clamps(plastic) anywhere. Thanks for replys

Thanks,

Kenny
 
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  #2  
Old 06-26-02, 07:38 AM
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LouieS
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The type of boxes you have bought are for use with non metallic flexible tubing and fittings. However, there are plastic cable connectors that may work. Look for T&B 3201 and another by Dottie.

I agree with the local. You cannot have isolated metal parts of conduit/cable system. The metal clamp is a highly likely place to have an insulation problem.
 
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Old 06-26-02, 08:20 AM
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Almost all the plastic boxes sold at my Home Depot have their own plastic cable clamps built-in (really just two plastic flaps through which you insert the NM cable). There are four such spots provided in each box to insert cables (one at each back corner). These flaps allow you to insert the cable, but resist moderate attempts to pull the cable back out. Do you not have these type of boxes available?
 
  #4  
Old 06-26-02, 08:27 PM
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bungalow jeff
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I have seen plastic boxes with plastic connectors in books, but never in the shops my way. Just the plastic boxes with the ears as John Nelson said. I'm sure a pro could get them from an electrical supply, but I am keeping this in the DIY context.
 
  #5  
Old 06-27-02, 04:04 PM
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Wgoodrich
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250.86
Exception No. 1: Metal enclosures and raceways for conductors added to existing installations of open wire, knob and tube wiring, and nonmetallic-sheathed cable shall not be required to be grounded where these enclosures or wiring methods
(a) Do not provide an equipment ground;
(b) Are in runs of less than 7.5 m (25 ft);
(c) Are free from probable contact with ground, grounded metal, metal lath, or other conductive material; and
(d) Are guarded against contact by persons.
Exception No. 2: Short sections of metal enclosures or raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be grounded.
Exception No. 3: A metal elbow shall not be required to be grounded where it is installed in a nonmetallic raceway and is isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the elbow or is encased in not less than 50 mm (2 in.) of concrete.

Hope this helps

Wg
 
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Old 06-28-02, 04:26 AM
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If possible to do so, can't the wire just be stapled within 8" of the box to secure it?
 
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Old 06-28-02, 07:31 AM
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MTgets
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I believe LouieS had it right, everyone assumed kpell meant the single or double gang device box with the breakout tabs, Ill bet he saw a 4 square box with 1/2" knockouts for fitting and pipe.

kpell they do sell NM cable plastic clamps that will fit in the 1/2" knockout, no locknut just tilt and snap in, then run the nm thru and sqeeze the tab to lock them in.
You have to make sure that this box is accsecilbe if behind drywall and they do have plastic raised covers (mud rings) to leave access with a blank cover.
 
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Old 06-28-02, 07:43 AM
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LouieS
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booman,

What kind of box are you using? From you asking about clamps in the first post I assumed that you'd grabbed the boxes with round knock outs designed for use with electrical non metallic tubing.

Normal plastic boxes intended for non metallic cable of the one gang size have 4 very small knock outs just big enough for a couple of non metalic cables. No clamp is needed and the staple must be close as you say. For larger boxes the small holes have a simple pressure clamp built in.

Wg,

It doesn't sound like that section you quoted covers this installation as the poster implies that this is newly wired area using new boxes and new romex but I can't find anything to back my view that the cable clamps must not be conductive when used with plastic boxes.
 
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Old 06-28-02, 12:19 PM
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Wgoodrich
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LouieS, Reread the first sentence of that rule I provided and you shoiuld pick up that this sentence pertains to new installations to an existing structure's wiring system. Look at that sentence part copied below from my previous post and see if that helps. Note that is says conductors added to existing installations. I believe that was what was being discussed was an older home as far as I was picking up.

Copied section of NEC 2002
250.86 exc 1
Metal enclosures and raceways for conductors added to existing installations

As for new installations in a new structure the same thing applies but not sure which rule says it. Just remember the term short sections of conduit fittings etc. being in the sentence pertaining to new construction projects. A half inch romex connector isn't going very far for carrying current. I believe that is what they are referring to in intent in both new and old installations.

Hope this helps

Wg
 
  #10  
Old 06-28-02, 03:25 PM
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LouieS
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Wg,

The poster sounds like he is wiring up several new boxes with new romex so he cannot use exception 1 because of (a). This newly added electrical must be grounded right? That rule is to give us a break when rerouting a minor bit of wiring in an existing ungrounded installation such as knob and tube or old romex. There is no way I could pass inspection here wiring up a whole new room or even adding some new boxes in a room and claiming that it is an existing installation. Exception 2 is used here to allow you to protect a romex cable from abuse or to penetrate a firewall without having to run the entire section of that circuit in conduit.

This is interesting Wg. I cannot find anything that says a metal clamp/connector can't be used so it must be OK but I don't agree that exception 1 says it is OK.
 
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Old 06-28-02, 07:05 PM
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Originally posted by boman
If possible to do so, can't the wire just be stapled within 8" of the box to secure it?
What kind of box are you using? From you asking about clamps in the first post

Actually LouieS, I was not asking about clamps. I was just asking a guestion in regard to the first poster's post. I was wondering if the staple within 8 inches would be okay with either metal or plastic.
 
  #12  
Old 06-28-02, 09:18 PM
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LouieS
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sorry boman. I got confused when looking at previous posts.

An approved cable clamp is required to attach non metallic cable to a box with the round knock outs.
 
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Old 06-28-02, 09:40 PM
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Glad I went ahead and got them. Rather safe than sorry!
 
  #14  
Old 06-30-02, 07:28 AM
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kpell
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Sorry it took me so long to get back with you, I've been sick for the past week. The boxes I am referring to are square plastic boxes (about 4x4x1 1/2) with 7 knockouts on them, The have two plastic tabs sticking out along one side so they can be screwed to a surface. they have two knockouts on each of the sides(the sides other than the one with the tabs) and one on the bottom, this box is the kind with the top that attaches with screws(2). I've went ahead and installed metal nm clamps in the boxes and I hope this is correct, I'm not so sure now because of all the posts. Anyways if there is any more info I can supply you with just ask.

Regards,

Kenny
 
  #15  
Old 06-30-02, 09:00 AM
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MTgets
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kpell,
like I said earlier, they sell plastic NM cable clamps, if you are concerned about the metal ones, they are widely used in bringing home runs to the panel on new construction.
 
  #16  
Old 06-30-02, 11:26 AM
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kpell
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Not really concerned with the metal clamps as far as me goes, but, the inspector might be a different story. I have looked in 3 towns for the plastic nm clamps and have yet to find them, also I have looked for the boxes with the small knockouts and for the boxes with the built in clamps and have yet to find them either, the only ones I have found with the clamps are 1,2,3 gang boxes for outlets/recepticles. So that is why I got the plastic ones with the knockouts. I hope he doesn't make me go change every one of them but if he does I will ask him where to get the correct clamps.

Thanks again

Kenny
 
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