Bond NM Cable Clamp in Plastic J Box???

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Old 08-10-08, 04:55 PM
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Bond NM Cable Clamp in Plastic J Box???

For an interior application (unfinished basement), I need to splice a 6/3 NM w/gr to lengthen a circuit. That's in one location. In another location, I'll need to splice the same cable to individual THWNs to transition to conduit. Because of the size of the conductors, I plan to use standard Carlon 6x6x4 plastic box, drilling holes for NM/SE cable clamps for the entrances to the box.

Is it a national code requirement to bond these cable clamps to ground? I've searched several electrical supply houses for bonding locknuts, all but one said they had not heard of them. One knew what it was but only carried 1/2" and said that is all they had ever seen. I tried to use the T&B connectors below, but they seem to only be desiged for metallic boxes, the walls of my plastic box are too thick:

http://www.grainger.com/Grainger/items/3LK42
http://www.grainger.com/images/produ...d/XL-3LK49.JPG

Any other non-metallic cable clamp methods?

If I don't have to bond, I'll just use 3/4" NM/SE clamps. If I must bond, what are my options?

Many thanks, RJ
 
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  #2  
Old 08-11-08, 08:13 AM
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The cable clamps probably should be bonded. I'm surprised you've been unable to locate bonding locknuts; this is a commonly used item on service entrance conduits. Perhaps they don't carry them in 3/4" though.

Why not just use a 4-11/16" square x 2-1/8" deep steel box with flat cover? This is a standard size box which can accommodate up to (8) #6 conductors, which is enough for your splice.

Make sure to get the correct size wirenuts. Only a few of the jumbo ones are rated for (2) #6 conductors. I think the biggest Buchanan brand wirenut can do it.
 
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Old 08-11-08, 08:49 AM
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Ben,
Many thanks for your insight.

Originally Posted by ibpooks View Post
The cable clamps probably should be bonded. I'm surprised you've been unable to locate bonding locknuts; this is a commonly used item on service entrance conduits. Perhaps they don't carry them in 3/4" though.
When I asked for bonding locknuts, most everyone thought a bonding threaded bushing. But since it bottoms out, it's not good for locking down a cable clamp to a box wall. Yesterday, Sunday, I thought to just get some and grind out the bushing part, but the big box centers didn't have anything smaller than 1-1/4.


Originally Posted by ibpooks View Post
Why not just use a 4-11/16" square x 2-1/8" deep steel box with flat cover? This is a standard size box which can accommodate up to (8) #6 conductors, which is enough for your splice.
I chose the larger box because I was trying to make more finger room for working the #6, and also to use these:
http://home.mindspring.com/%7Erjs/3044160_UT10.pdf
instead of wire nuts. I have enough of those blocks, and believe these will give me a more solid connection. But, I have some Ideal wirenuts rated for 2 #6 as a fallback plan.

Are there any larger size standard metal boxes? I looked a little, but it seemed the PVC boxes were easier to find in larger (6x6x4) sizes. I don't mind if the boxes don't have knockouts, I have a Greenlee punch for 3/4. I don't care if the boxes are a few bucks more, I want the job to meet code and to give me room for my amateur fingers; the PVC ones were $8 at the big box!

Thanks, RJ
 
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Old 08-11-08, 09:57 AM
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The 4 11/16 is pretty common size to use with #6's but yes there is larger metal junction box but normally useally found in electrical supply centre most big box store don't stock larger than 4 11/16 metal box.

Some of the larger metal juction box do have KO's ready and some don't have the KO on them.

For some reason if you get the without the KO's you will need a holesaw or punchdie to make a hole for it and punch it out.

Merci,Marc
 
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Old 08-11-08, 11:15 AM
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Metal boxes come in many sizes. Sometimes the big box stores have them, but any supply house should. With 4-11/16 boxes, you can also buy an extender which is basically a second box with no back thus doubling the depth.
 
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Old 08-11-08, 11:29 AM
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Remember that those 'DIN rail contacts' that you are considering using must be mounted on a rail; so in addition to the contacts you will also need to mount a rail at the back of the box.

I've never seen those contacts used for building wiring, but I've used them many times in control panels. My hunch is that they are legal but would raise a red flag with any inspector because they are not generally used in this application.

If you want an easy to use splicing method for large conductors, I recommend insulated the various insulated set screw connectors, for example http://www.polarisconnectors.com/370...L_EXTRA_IT.pdf

With these connectors, you have the simplicity of the terminal blocks, no worries about taping or adding insulation, they are free hanging, and they are expected in this sort of application.

For the box, there are numerous sources for larger metal junction boxes. If you don't mind paying a premium for a catalog supplier that has most everything, check out www.mcmaster.com. Additionally there is a store on this site (doityourself.com) that may have what you are looking for.

-Jon
 
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Old 08-12-08, 04:44 AM
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Jon,
Many thanks for your ideas. I've got the rails for the DIN blocks, the perforated ones for easier mounting. Also the right size blocks with US colors and also grounding blocks. I use these for control panel applications also, so they are readily available to me. They have a bunch of compliances, including UL, but I don't know if specifically listed for residential applications. I agree that a typical jurisdiction elect inspector will scratch his head over them. I just really like their compact size, neatness, and robustness for this circuit (50A spa service.)

I initially looked at the Polaris connectors, I think Ben or Marc oointed me to them, but they are so expensive. I think I should look at them again, since they certainly have the robustness I'm looking for, and probably more familiar to inspectors.

Thanks for the M-C point. I never thought of them for straight electrical supplies, always thought of them as a cross between Mouser/Newark and Grainger. I think these NEMA 1 boxes at the top of the page is just what I'm looking for:
http://home.mindspring.com/%7Erjs/McMaster_page0816.pdf
In a 6x6x4 size, that gives extra room to make the splices. I'll try to get by a local supply house today to see what they have, otherwise will order from M-C. I looked at the DIY site, didn't seem to get this specialized.

Thanks again, RJ
 
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Old 08-12-08, 07:31 PM
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Rj.,,

I just want to give you a head up the Polairs connector it is far more common and many inspectors are famimuair with it and they will pass it with no issue with this set up.

Now for the metal box size the electrical supply will carry various size on hand and yeah the 6X6 is common one they stock bunch of them.

That is plenty room for the #6 wire to play around.

Sure the Polairs connectors are more expensive but in long run it much neater and quicker so you don't have to deal with the split bolt and electrical tape wrapping and if not done right it can come back and tick ya off with it { I did see it happend quite few time }

Merci,Marc
 
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Old 08-12-08, 09:46 PM
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Marc,

RJ is planning on using 'DIN rail' barrier terminals, such as are common in Europe and common in control panels in the US. I see no reason that they would not be useable in NEC compliant wiring, although I don't know for sure that they have the proper listings.

I think that such terminals would be as easy to use as Polaris connectors, and would have the benefit of being solidly held in place in the junction box, thus there would be no issue with having to push the splice back into the box.

I guess that because they are fixed in place, that the junction box would need to be large enough to provide 'wire bending space' between the box walls and the terminals...which might be larger than a box normally needed for the same size wires.

My biggest concern is that they would look strange to any inspectors, and might raise a red flag with the inspector.

-Jon
 
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Old 08-12-08, 10:01 PM
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Jon { Winnie }

That part I do agree with you myself I have no issue with the termial block { I am oringally from France and they are widespread in that area }

with the DIN rail the smallest size with #6's is 6X6X4 otherwise 8X8X4 will meet this without any effort.


Yeah with some inspectors they may not well aware with the DIN rail termail block they are allowed per NEC code { it not a widespread useage in resdentinal area }

If the OP talk to the inspector about this in ahead of the time I am sure it will work out ok by time.

Merci,Marc
 
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Old 08-13-08, 11:53 AM
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Marc, Jon,
Thanks for your thoughts. I think we all agree that the DIN rail blocks are a good solution for the circuit. But the inspectors will potentially question it or wonder about it. While my day job involves electrical construction and use DIN blocks all day long, I am not a licensed electrician and I'll be doing this work under a homeowner permit. So I prefer not to give the inspectors something to think about.

I also agree with the action of talking with the inspector/management of my jurisdiction, but unfortunately here in metro Atlanta the inspection/permit departments are very busy and overworked, and extremely hard to get to the inspectors themselves (permit clerks to take your money - those are easy to find!) I will try to get a discussion with the chief or supervising electrical inspector, but I am not certain I can get make that happen. I can be onsite when the electrical inspector comes, but my work will be done at that point.

I thought about setting the circuit up with wirenuts for inspection, then putting in the DIN blocks after inspection, but I'm not fond of that underhanded tactic.

I really like the Polaris connectors and would thoroughly trust them, even though the finished installation takes up more space than rail-mount. But space is not my issue (since I found the metallic boxes at McMaster). Since I have one splice point and one transition (to THWN) point, I'm looking at 8 Polarix IT4, which runs over $100! I already have the DIN blocks and rails, so cost is zero.

Split bolts wrapped with electrical tape, IMO, is only one short step above wirenuts: electrical connection is better than wirenuts, but tape wrapping does not give me comfort. I really want something more rugged like a terminal/power block.

I am thinking about Marathon 1104 or 1204. I would still need to purchase, but even from Newark two 1104 blocks is less than 1/3 the cost of 8 IT4s. I am assuming that I have a better chance of the average inspector being more familar with power blocks than rail-mount blocks. What do you guys think?

Thanks again, RJ
 
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Old 08-13-08, 12:44 PM
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Given that you have the materials already, I would take the gamble and go with the DIN connectors. Just be sure to print out the specification sheets to show the inspector if asked.

The worst case is that you will have to pull the DIN connectors out and put in the Polaris connectors, which would be expensive in terms of time and a possible re-inspection.

The best case is that you will start a trend and we'll start seeing DIN hardware used in residential applications in the US.

I disagree with you on 'I really like the Polaris connectors and would thoroughly trust them, even though the finished installation takes up more space than rail-mount.' With the polaris connectors, you have a free hanging splice, and thus you simply need to meet the box fill requirements. But with the DIN connectors you have a terminal that is in a fixed position in the box...which in my mind brings the various 'wire bending space' requirements into play. My strong hunch (I've not done the calculations) is that the minimum required box size for the Polaris splices will be smaller than the minimum required box size for the DIN connectors.

I know that you will be using a grounding terminal block; but make sure that you properly bond the DIN rail to the box.

Remember that the minimum length for spliced conductors requires that they extend at least 6" out from the face of the box. This probably means that they will need to fold over inside the box on the way to the terminal blocks.

-Jon
 
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Old 08-13-08, 07:19 PM
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Jon,
Thanks!

Yeah, I see what you mean about the space requirements. I was thinking of the polaris being unmounted, with four individual units on rather stiff conductors, and therefore shoved rather unceremoniously into the box. But you're right about the conductor "dressing" space on their way to the DIN blocks. Here is a drawing a did a little while back, when I was asking if I needed SE cable clamps (so ignore the "plastic box" and "hole in box" notes. Also, I don't know where that blue line came from, I don't recall that on the original, but I'm not at the computer with the original visio file.)
http://home.mindspring.com/~rjs/splice+box.pdf
I have never looked in the NEC for bending radius requirements for simple conductors, can you point me to the article/subarticle?

And thanks for the reminder to ensure the 6-inch out of box removal.

Thanks, RJ
 
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Old 08-13-08, 07:39 PM
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RJ,..

The wire bending radius is useally 6X of the conductor diamaiter so with the #6 conductors they are about 3/8 inch diamaiter so you can bend about 2.5 inches or so any tighter than that it may crack the insulation materal.

When you plan to use the DIN mount make sure you don't have sharp corner hitting the conductor { wire } and pitch it.

Otherwise you are good to go 6X6 is the min size with DIN mount otherwise " 5X5 " AKA 4 11/16 box will useally do very good with polairs connectors.

Merci,Marc
 
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