Multiple cables through single knockout

[JOEE]

Hello,

Different people (Engineers & Electricians) give me different answers on this, but who is really right? My question is - can two NM cables be pulled into one knockout in a metal 1900 box? This is a standard 4" box with the preinstalled clamps, two openings on top and two on the bottom. The scenario is three NM cables only coming into the top of the box. Can two be pulled in one and the one in the other? I know that 314.17(C) states that this meets code for nonmetallic boxes, but is it also true for metallic boxes?

 

[bphgravity]

Follow the manufacturer's instructions...

 

[JOEE]

Follow the manufacturer's instructions...

The manufacturer of the 1900 box? My question is a general code question for metallic boxes. Can 2 Romex cables be brought into the same knockout in a metallic box? The person that I work for prefers it that way, with all cables entering from the top. I never questioned it until today when I read something in a code-interpretation book stating this exception only applies to nonmetallic boxes. Did I misread this? The author quotes it from 314.17(C), but when I went there in the handbook I didn't see it.

 

[JohnJ0906]

My opinion is No, if you are using the romex clamps with the box UNLESS the manufacturer says its OK. However, I couldn't find anything in the code myself. If I was going to bring 3 wires in the top I would use connectors

 

[infinity]

I agree with John, the manufacturer of the box would have to list the cable clamps as suitable for more than one cable per opening.

 

[volt102]

Follow the manufacturer's instructions...

Like Bryan said.....Follow the manufacturer's instructions.

Jim
New Hampshire

 

[Pierre C Belarge]

From the 2006 UL White Book (an excellent source of information, and available for free from www.ul.com as either a PDF and/or in book form)

Page 192-193
METALLIC OUTLET BOXES (QCIT)

Clamps
Clamps have been tested for securing only one cable per clamp, except mulitple section clamps are considered suitable for securing one cable under each section of the clamp, each cable entering a separate knockout.

 

[dnem]

The last sentence of 314.17(C)X specifies that "Multiple cable entries shall be permitted in a single cable knockout opening" for a nonmetallic single gang box. . So the answer is given for the nonmetallic single gang.

But that doesn't mean that multiple cables in a single KO in any other box is prohibited. UL says that "Clamps have been tested for securing only one cable per clamp" but that doesn't mean that multiple cables per clamp will fail to secure properly, it only means that the clamps have been tested for securing only one cable per clamp. . Multiples in a single KO weren't tested.

110.3(B) says to follow the listing or labeling of the equipment. . The last sentence of 110.3(A)(1)FPN says "Suitability of equipment may be evidenced by listing or labeling". . But if multiples in a single KO are not addressed by the manufacturer then you have to drop back to 110.3(A).

110.3(A)(2) says to look at mechanical strength.
110.3(A)(5) says to take into considereation heating effects. . This would be a similiar situation to the one in the second paragraph of 334.80.

It looks to me like a situation were there will varying opinions. . Hopefully the manufacturer has addressed it.

David

 

[dnem]

I've been thinking about this situation on and off over this past day, wondering how I would react if I saw it on an inspection.

As an inspector, if I'm not ready for the worst case scenario then I know that's exactly what I'll be faced with that very same day. . So let's just go with the worst case. . Let's just say that manufactures info doesn't comment on suitability of multiple Romexs in a single steel connector or a single plastic push-in connector in a steel box. . No info at all.

I would then be thinking about 110.3(A)(2) and (5).
110.3(A)(2) says to look at mechanical strength.
I can't imagine that a steel Romex connector would have less mechanical strength than the near useless flaps in a nonmetallic box, so I don't see an issue there.

110.3(A)(5) says to take into consideration heating effects. . 334.80 says that Romex has a 90? rating which would be 14gauge=25a 12gauge=30a. . Table310.15(B)(2)(a) says that you can install up to 9 current carrying conductors and not have to derate more than 70%.

14gauge
25a
x70%
=17.5a
So you can still land it on the 15a breaker.

12gauge
30a
x70%
=21a
So you can still land it on the 20a breaker.

I don't see any heating effects issues either.
So I wouldn't have a problem with the installation even if there wasn't any manufacturers specs. . I would pass the install based on everything that I've thought about up to this point.

David

 

[infinity]

Dave I agree with you from a logical perspective:

I can't imagine that a steel Romex connector would have less mechanical strength than the near useless flaps in a nonmetallic box,

If the cable were stapled near the box with the metal connector with two cables this would still be mechanically superior to the broken flaps. But is it supported by the code?

Also I wouldn't worry about derating into a connector. Derating factors don't apply until after 24" of conduit or bundling. A chase nipple can be filled to 60% fill without any required derating. Even if it contained 50 CCC's.

 

[Ragin Cajun]

Nice to know what I've been doing for years is ok. I do limit to 2 NM's through fittings on panelboard walls. The "instructions" say 2 is ok.

My general thanks to this forum for it's helpfulness!

RG

 

[dnem]

Also I wouldn't worry about derating into a connector. Derating factors don't apply until after 24" of conduit or bundling. A chase nipple can be filled to 60% fill without any required derating. Even if it contained 50 CCC's.

I'm assuming that you're referring to Chapter 9 Notes to Tables (4) which specifically exempts the 2 foot nipples from 310.15(B)(2)(a).

But 334.80, paragraph 2, says to apply the Table310.15(B)(2)(a) adjustments to wires "bundled together and pass through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam". . It doesn't indicate that it would only apply to a wood penetration that is more than 2 feet long. . I can't even picture anyone ever drilling thru wood for more than 2 feet.

So the question is:
Is a box connector more like a conduit nipple or more like a firestopped wood penetration ?
No matter how you look at it, it looks like a code compliant install.

David

 

[allenwayne]

What NM box connector allows you to have more than 9 CCC`s ???? Even if you were able to drill through 24 +/- ins and enter a box with a connector.If I am not mistaken 4 2 wires is the max for all NM box connectors.I had a listing awhile back but can`t find it now.

 

[allenwayne]

arligtons site says 4 14/2`s is the max http://www.aifittings.com/c_19.htm

 

[dnem]

What NM box connector allows you to have more than 9 CCC`s ???? Even if you were able to drill through 24 +/- ins and enter a box with a connector.If I am not mistaken 4 2 wires is the max for all NM box connectors.I had a listing awhile back but can`t find it now.

9 was just looking at the derating situation.
If you get into wirefill you'd have to determine the capacity of the connector and then even move into looking at the box. . Boxwise, with the 9, you'd have to count at least one equipment ground and probably another 2 for the yoke, so you have 12 or more X 2 (14gauge) or 2.25 (12gauge) [Table314.16(B)].

So your box would need to be 24 to 27 sq"

My point is that this can be drawn out to include as many factors as we can think of but the end result is that the AHJ has to make a call on the 2 Romexs in one connector and looking at stuff like 334.80 helps in applying 110.3(B).

David

 

[dnem]

arligtons site says 4 14/2`s is the max http://www.aifittings.com/c_19.htm

What does a BT50 look like ?

 

[JOEE]

Thanks for all the info. I'm glad I turned to you guys for advise. The 1900 box that I was referring to is the RACO 223, which is the basic 1900 for NM cables. It has 1/2" KOs and 4 priouts with clamps. I tried called RACO out of curiosity, but they haven't returned my call yet.
We have been doing this for a long while and haven't failed any inspections because of it, but that paragraph that I read in a code-intrerpretion book is what threw me off.

 

[LarryFine]

What does a BT50 look like ?

From this page: http://www.aifittings.com/c_10.htm

AKA the ubiquitous "Tomic."

 

[infinity]

I'm assuming that you're referring to Chapter 9 Notes to Tables (4) which specifically exempts the 2 foot nipples from 310.15(B)(2)(a).

So the question is:
Is a box connector more like a conduit nipple or more like a firestopped wood penetration ?
No matter how you look at it, it looks like a code compliant install.

David

What I'm saying is that you could put 100 current carrying conductors through a nipple and not worry about derating, so why should there be a concern about derating for multiple cables into a connector.

 

[allenwayne]

Trevor the question is not about nipples but cable clamps.Be it integral nm clamps or ko clamps.What are they listed as far as capacity goes.I would have to say that if the listing has been tested for one nm cable under each clamp,then to place 2 cable assys. under that same clamp would be a violation of the listing.Since they have only been tested with that one cable under the clamping device.To say if they are strong enough for one then they will be ok for two is a silly argument.Why stop at 2 why not 3 or 4 or 5 if the fit.
Just because there are 4 openings in a 1 gang NM box doesn`t mean that you can put 4 12/2`s and a device in that box.