Terminating MC cable grounding conductors

[coulter]

This a little long and involved, but if it were easy...

Background: We use a lot Okonite CLX. It is an MC-HL, continuous sheath MC, listed under UL1569. In a three conductor cable, the grounding conductor is split into three sections, set into the interstices. The three added together meet the requirements of 250.122. This construction clearly meets the UL requirements.

We have been using this cable for quite a few years. The practice was to take the three grounding conductors, chuck the ends into a cordless drill, and twist the three tightly together, and terminate under one mechanical, setscrew type lug. The method produces a nice nearly round, stranded, single conductor - looks good, works well.

Recently the AHJ decided we were incorrectly terminating the grounding conductors. As near as I can tell, the issue is the lugs are listed (labeled - marked?) for only one conductor and the cable has the grounding conductor split into three sections. He insisted we use a three hole lug and pick up each section separately. Okay, we can - most times; not always easy - say coming into a disconnect there isn't a lot of room. And if there is space, one could always pick up the three, along with a suitable sized single conductor, under a split bolt and terminate the single conductor - messy looking cludge, but possible.

The thought had never occurred to me this could be an issue. We hire good journeymen, they do good work; my inclination is to stay out of their way, especially on craft issues.

However, when this came up, I reviewed the CLX product data sheet, the Okonite cable handbook, UL 1569, and the NEC. The Okonite literature does not give any specific instructions on terminating the three. My interpretation of UL 1569 is they intended the three sections to be treated as one grounding conductor - since each section by itself is too small to meet 250.122. I couldn't find anything in the NEC that really addresses it.

I think our practice is good workmanship and meets the intent of the code, but if the AHJ says we are not meeting the letter of the NEC, then we aren't - he is the one with the hammer. However, he and I generally have cordial, polite conversation, and he responds to gentle discussions with code books in hand. I think we have an unspoken agreement, "I don't p--s him off, and he doesn't get stuck."

The Questions:
1. For those of you using an MC cable with sectioned grounding conductors, how are you terminating them?

2. I am not seeing the safety or reliability is improved by terminating the three separately. Am I missing anything here?

3. Can anybody lead me to references that show methods of terminating the three? Maybe I missed something in the NEC -- or there are common practices shown in journeyman handbooks, or even other cable mfgs literature.

We aren't stopped here, nor in trouble, but I would still like to know if I am goofed up, or get some clues as to reasonable arguments that what we have been doing is okay. Any help on this will be graciously appreciated.

carl

 

[iwire]

Re: Terminating MC cable grounding conductors

I wonder if he would have you use individual lugs for the bare in SE that we all twist together and place under one lug?

 

[bphgravity]

Re: Terminating MC cable grounding conductors

Per the PJAZ.guideinfo, "The equipment grounding conductor required within all other cable with interlocked armor may be insulated or bare, may be sectioned..." It then goes on to say, "The supplemental grounding conductor may be sectioned".

This to me means that together the individual sections make-up the one EGC. It deoesn't indicate that each should be considered EGC's individually. Similar to SE as mentioned by Bob.

I feel it is not a violaton to combine the three into one conductor and terminatre as one. I see no hazard in doing so.

 

[kiloamp7]

Re: Terminating MC cable grounding conductors

Obviously, clean, tight, electrical connections are the bottom line.

 

[rbalex]

Re: Terminating MC cable grounding conductors

In UL terms the ??one mechanical, setscrew type lug,? you have described is a terminal connector. (UL Category Code ZMVV)

Such connectors are ?marked? as follows:

Wire size and wire combinations ? Wire connectors are rated for 30 AWG or larger copper conductors and/or 12 AWG or larger aluminum conductors. The wire size, wire range or wire combinations are marked on the connector, or on or within the unit container. Wire connectors additionally investigated for metric size conductors are marked with the metric wire sizes expressed in mm2.
Multiple conductors ? Connectors generally accommodate a single conductor under a clamping mechanism unless otherwise identified, such as with the number of conductors located parenthetically in front of the wire size or range. Some connectors may have a single conductor wire range as well as a second multiple conductor wire range. Some connectors, such as twist-on connectors, will have multiple conductors expressed in a list of wire combinations.
Parallel conductors ? Connectors intended for paralleling of conductors are intended to be used in accordance with Clause 310.4 of the NEC. Parallel connectors may have multiple conductor clamping mechanisms, each accepting a single conductor or a singular clamping mechanism accepting multiple conductors.
Wire stranding ? Unless clearly marked "Solid," "SOL," "Stranded" or "STR" for a given wire size, wire range or wire combination, conductors in the range 30-10 AWG are both solid and stranded, and 8 AWG and larger are for stranded wire only. Connectors additionally rated for metric conductor sizes are marked with the letter "r" for rigid solid and rigid stranded conductors, or the letter "f" for flexible conductors.

I would submit that where the three separated equipment grounding conductors are combined to form a single conductor within the ?wire range? of the "Wire size and wire combinations" it meets the intent of both UL and the NEC as long as all strands are included in the termination.

[ November 29, 2004, 02:37 PM: Message edited by: rbalex ]

 

[john m. caloggero]

Re: Terminating MC cable grounding conductors

The sectionalized equipment grounding conductor is treated as a single equipment grounding conductor and is sized in accordance with Table 250.122. Since the EGC consists of multiple strands, the terminating device must be suitable for use with stranded conductors. Terminals designed for termination of stranded conductors are provided with a saddle to protect the conductors from damage when the set-screw is tightened.

 

[sandsnow]

Re: Terminating MC cable grounding conductors

Your inspector can query UL on this as can the manufacturer. It ca be done via-email and is pretty timely. As a contractor, I don't know what their response policy is. You could try the local IAEI meeting and see if there is a UL rep in attendance. IAEI meetings usually have "contractor time" for just this type of thing.
I would have to put my vote to treating it as one conductor for termination purposes.
If you want to get technical, then the "size" of the three conductors would have to be stated on the jacket or somewhere to properly size the terminal.
UL usually requires instructions for installation when the proper method cannot be determined from the NEC. Maybe this was overlooked or thought to be obvious. I think maybe the latter and your inspector may be overthinking things.

 

[pierre]

Re: Terminating MC cable grounding conductors

John
The saddle you mention - I am not familar with this type of lug. I have seen the lugs that look (for lack of a better term) like the four leaf clover without the stem. I thought these were designed in this fashion for more than one conductor.
what is the saddle type, and is it possible to provide a link so we/I can see what one looks like?

Pierre

 

[coulter]

Re: Terminating MC cable grounding conductors

Guys and girls -

I learning here with each post. All comments/references are helping.

Tell you where I am so far:

IW - Don't laugh. I'm not sure I have ever seen a piece of SE that I knew what it was.

BP - What is "PJAZ.guideinfo"?

Sand - I had not thought of sending a query to UL. I'll give that a try. I have a query into the cable mfg to see if they have any "secret instructions"

As far as the cable markings, yes the size of the individual rounding conductors is on the cable jacket. For example, 3C - 750 CU, says "with 3 - #5CU ground"

working

carl

 

[rbalex]

Re: Terminating MC cable grounding conductors

I should have added this web page in my first reply.

Go to it and enter "PJAZ" in the Category Code window. Make sure you also check the "Display Guide Info only" box or you will get more info than you need at the moment. Try "ZMVV" too.

It will return the UL General Information catalog data. This info may contain installation/application requirements enforceable through NEC Section 110.3(B).

Without the "Display Guide Info only" box checked it will also return every manufacturer that makes items under the Category Code. UL updates this info almost daily.

 

[iwire]

Re: Terminating MC cable grounding conductors

Originally posted by coulter:
IW - Don't laugh. I'm not sure I have ever seen a piece of SE that I knew what it was.

Not laughing, that makes us even, I work with MC all the time but have never seen the type you describe.

Here is a piece of typical SE cable.

You can see that the bare grounded and /or grounding conductor is wrapped around the outside of the insulated ungrounded conductors.

The normal method is to twist these all together and place under one terminal.

I feel this is the same as what john m. caloggero was pointing out. It is one conductor not multiple conductors.

Good luck, Bob