2014 Article 314.16(B)(2)

Status
Not open for further replies.

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I know we have talked about this but this change seems absurd. As I read this it seems to say the volume marked in these plastic boxes is not the true volume so we have to deduct the clamp intrusion into the box but we don't have to count the intrusion as 1 conductor. If this is so why doesn't the manufacturer just mark the box with the actual volume of available space. Am I reading this correctly?


314.16(B)(2) Clamp Fill. Where one or more internal cable clamps,
whether factory or field supplied, are present in the box, a
single volume allowance in accordance with Table 314.16(B)
shall be made based on the largest conductor present in the
box. No allowance shall be required for a cable connector with
its clamping mechanism outside the box.
A clamp assembly that incorporates a cable termination
for the cable conductors shall be listed and marked for use
with specific nonmetallic boxes. Conductors that originate
within the clamp assembly shall be included in conductor fill
calculations covered in 314.16(B)(1) as though they entered
from outside the box. The clamp assembly shall not require a
fill allowance, but the volume of the portion of the assembly
that remains within the box after installation shall be excluded
from the box volume as marked in 314.16(A)(2).
 

LEO2854

Esteemed Member
Location
Ma
I know we have talked about this but this change seems absurd. As I read this it seems to say the volume marked in these plastic boxes is not the true volume so we have to deduct the clamp intrusion into the box but we don't have to count the intrusion as 1 conductor. If this is so why doesn't the manufacturer just mark the box with the actual volume of available space. Am I reading this correctly?


314.16(B)(2) Clamp Fill. Where one or more internal cable clamps,
whether factory or field supplied, are present in the box, a
single volume allowance in accordance with Table 314.16(B)
shall be made based on the largest conductor present in the
box. No allowance shall be required for a cable connector with
its clamping mechanism outside the box.
A clamp assembly that incorporates a cable termination
for the cable conductors shall be listed and marked for use
with specific nonmetallic boxes. Conductors that originate
within the clamp assembly shall be included in conductor fill
calculations covered in 314.16(B)(1) as though they entered
from outside the box. The clamp assembly shall not require a
fill allowance, but the volume of the portion of the assembly
that remains within the box after installation shall be excluded
from the box volume as marked in 314.16(A)(2).

That looks like bad English to me, the wording is confusing by starting off the second half of the sentence with the word "but" just to tell you the same thing as in the first half of the sentence :blink:

Is that what you see Dennis?
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
I see this as saying you have to deduct the internal part that cuts into the rectangular space of the box.
You seem to be describing the factory molded portion of a nonmetallic box that can act as a clamp.

The 2014 NEC 314.16(B)(2), on the other hand, in having a whole second paragraph concerned with the two word term clamp assembly , I think, is describing something that is NOT an integral part of the box as manufactured.

Rather, the clamp assembly "shall be listed and marked for use with specific nonmetallic boxes." Meaning it is a clamp that can be installed in more than one nonmetallic box, so it has to be an added part, not an integral part of a box.
 

kwired

Electron manager
Location
NE Nebraska
You seem to be describing the factory molded portion of a nonmetallic box that can act as a clamp.

The 2014 NEC 314.16(B)(2), on the other hand, in having a whole second paragraph concerned with the two word term clamp assembly , I think, is describing something that is NOT an integral part of the box as manufactured.

Rather, the clamp assembly "shall be listed and marked for use with specific nonmetallic boxes." Meaning it is a clamp that can be installed in more than one nonmetallic box, so it has to be an added part, not an integral part of a box.

That is kind of how I have always understood it. Plastic clamp that is molded with the box is accounted for in the marked volume. A clamp that is not molded but is later added needs to be counted with conductor fill whether the clamp is factory or field added.

You need to pay closer attention to this clamp for fiberglass boxes then you do for plastic boxes in general as the clamps in most fiberglass boxes are not part of the box but are an added part. It may be possible though that some of those clamps need not be counted if not being used - may want to look at listed instructions for the box.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
You need to pay closer attention to this clamp for fiberglass boxes then you do for plastic boxes in general as the clamps in most fiberglass boxes are not part of the box but are an added part. It may be possible though that some of those clamps need not be counted if not being used - may want to look at listed instructions for the box.
The original "clamp" language in the first paragraph of 314.16(B)(2) is ancient, was developed for metallic boxes . . . is language originating before the advent of plastics and other nonmetallic materials. In my opinion, the applicability of just the original "clamp" language has always been a bit gray. I see the "shall be listed and marked for use specific nonmetallic boxes" as the heart of this new Code regulating the safer clamping of cables at nonmetallic boxes.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
We have this

785007207408lg.jpg



And we have this

plastic+electrical+box+2.jpg



And this

A058_1_20110420_b9bd7950-a3f4-4d64-a568-c1d5b6289992885639.jpg



So you guys think just the bottom pic needs to count the clamps?
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
And something like the T&B Carlon B234ADJC has even bulkier factory installed clamps listed for range cables:

A058_1_20110420_9012b11c-ecf1-41ae-8376-5fbd90182e01885657.jpg
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
So you guys think just the bottom pic needs to count the clamps?
No.

All of the "factory installed" clamps that both you and I have shown in the previous photos, I don't believe, are the "clamp assembly" described in 314.16(B)(2) second paragraph.

I understand the "clamp assembly" to be that clamp that could be installed in the box, below, or any similar to it.

b112hb_cl1


My experience is that most snap in cable clamps are designed for thinner walls that have cleaner edges than one experiences with K.O.s in nonmetallic boxes.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
That is to say, the older, original language of 314.16(B)(2) allowed us to use just any old thing that we could "get to stick" in the hole, but now, with the new language, because this is a nonmetallic box, the clamp has to be "listed and marked" for the specific box.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I see this as saying you have to deduct the internal part that cuts into the rectangular space of the box. NO

Yes, precisely. For other clamp situations the volume you deduct will depend on the size of the largest conductor in the box (whether it is associated with a particular clamp or not) and will be essentially one conductor allowance.
The "... BUT...." tells you not to take that full table allowance but instead to deduct the actual volume associated with the part of the clamp that is within the box. As if you had the tools to easily make that measurement and calculation.... :(
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
No.

All of the "factory installed" clamps that both you and I have shown in the previous photos, I don't believe, are the "clamp assembly" described in 314.16(B)(2) second paragraph.

I understand the "clamp assembly" to be that clamp that could be installed in the box, below, or any similar to it.

b112hb_cl1


My experience is that most snap in cable clamps are designed for thinner walls that have cleaner edges than one experiences with K.O.s in nonmetallic boxes.

If you use a metal switch box for mc cable I believe you count the clamp? So why not on the plastic.. This IMO is very poorly written or I am dense.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
If you use a metal switch box for mc cable I believe you count the clamp? So why not on the plastic.. This IMO is very poorly written or I am dense.
I wonder if this passage isn't a bit of the cart ahead of the horse. That is, much of what is going on is the shaping of manufacturer's offerings, many of which haven't been made yet (such as the "listed and marked" clamp assembly).

Here's an example, if cable enters the box at one or more hubs, of a nonmetallic box with threaded hubs that will have NO part of the clamp assembly within the volume of the box:

e382de_cl1
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I wish I knew Al. I think the idea was supposed to allow the clamps in the first two boxes I showed earlier without taking a reduction but it does not seem that way. In the 2011 some of the cmp members were saying we had to count those clamps since they were inside the box. I called the manufacturer and he said whatever the NEC says... no help there
 

kwired

Electron manager
Location
NE Nebraska
As always when something isn't clear AHJ is usually able to trump all possibilities:blink:

So if you want to push the fill on a particular box you may want to see what they have to say.
 
Status
Not open for further replies.
Top