250.118(10) MC Cable Equipment Grounding Conductor (EGC)

[lpfink]

We use MC-HL in Class 1 Div 2 locations on our equipment and use two different MC-HL cables. Both use a corrugated metallic sheath but the 1st type is filled with single conductors and includes a green insulated wire (wire type EGC) and the 2nd type contains twisted pairs or twisted triads with shielding and a drain wire for each pair or triad, along with an overall shielding and drain wire. My questions are related to 250.118(10):

1) Is there any MC cable where the metallic sheath ALONE is suitable to be used as the EGC? Seems like 250.118(10)(c) says there is if the metallic sheath is listed and identified as an EGC.
2) Brings me to my next question. UL1569 (Standard for Metal Clad Cables) section 6.1.8 says if the resistance of the metallic sheath is equal to or below on of the values in Table 6.1 - 6.4 it MAY contain an EGC, leading me to believe that the sheath ALONE is suitable as the EGC. The other sections of UL 1569 say SHALL contain.... Would a MC cable meeting UL 1569 be meeting the requirement from 250.118(10)(c) of being listed and identified?
Here is section 6.1.8 from UL 1569:

3) How would the requirements to bond/ground apply to the instrumentation cable MC-HL we are using, if you guys have any input. Put another way, wouldn't this type of cable need a combined wire type/metallic sheath if the metallic sheath ALONE wasn't suitable to serve as the EGC?

I will ask our supplier for the certificate of compliance to see if anything is mentioned but from our drawings I don't see anything. Thanks!!

 

[rbalex]

I guess this has festered long enough. I moved the thread from the Hazardous (Classified) Forum because it is more a grounding/bonding and product standard issue than hazardous locations.

First, a bit of history: I was instrumental getting the forerunner of MC-HL recognized in Division 1 in 1999. It was Section 501-4(a) Ex. No. 2. It was not my idea; it had been proposed and rejected in the 1996 cycle but I got the API Subcommittee on Electrical Equipment (SOEE) to support it for the 1999 cycle. I was also a principal reviewer of UL's original product standard for it. Had it gone through in its original form, you would have needed 19 feet of cable just to show all the markings that UL specified.:slaphead:

That said:

There are three basic forms of Type MC cable. See Section 330.116. Also see Section 330.108 and its cross-references to Sections 250.118(10) and 250.122. As you noted Section 250.118 (10) c indeed recognizes that some smooth and corrugated sheathes may be suitable as EGCs on their own. Type MC-HL uses a corrugated sheath; however, Section 501.10 (c) requires that it have a separate EGC in the core. CMP14 is paranoid about grounding/bonding and the belt and suspenders approach was required to sell it.

This also applies to Type ITC-HL for instrument/control circuits.

BIG NOTE: Any Type MC construction (HL or not) is acceptable in Division 2. If the sheath is listed as an EGC alone, it would be suitable. Section 501.30 (B) places no addition burden on Type MC beyond what is already required in Section 501.10.

On second thought - maybe I should have left in the Hazardous (Classified) Forum.

 

[lpfink]

Bob,

Thank you again for providing some interesting background! That's one reason I enjoy posting on here and reading so many of the posts as well.

I peeked at section 501.10(c) and also acknowledge your statement: "Any Type MC construction (HL or not) is acceptable in Division 2. If the sheath is listed as an EGC alone, it would be suitable."

Follow up questions:

1) How many examples of Type MC cable have you seen or may be out there where the sheath is listed as an EGC alone, or is it worded in a different way than that on a certificate or on the manufacturer's datasheet?

I'm looking at UL's PJAZ Guide Info on Type MC cable and also have looked through UL 1569 and don't see any additional requirements other than the resistance check in section 6.1.8 of UL 1569.

2) Would a manufacturer need to do additional testing to UL 467 for this sheath to be listed as an EGC?

3) Would section 501.10(c) also apply to MC-HL containing the twisted pairs/triads used in the Class 1 Division 2?

Thanks again and I know I have a lot of questions

Loren Fink

 

[rbalex]

1) I'm not generally in the habit of doing someone else's research for them. (I'm retired now) I can tell you that once MC-HL and TC-ER "hit the streets" there was a small revolution in the industry some 10 to 15 years ago. Those that made MC-HL successfully basically stopped making "standard" corrugated MC and those that made TC-ER stopped making "standard" TC. Of course that's not entirely true, they could still make the "standard" product but they rarely marketed or stocked it since the "-HL" or "-ER" product could still be used as the standard product and the actual cost of maintaining (especially stocking) two lines of product was often cost prohibitive. The actual differential cost of manufacture was apparently minimal, the real cost was NRTL certification. (I can be challenged on this; I'm not a manufacture although I was a major proponent of both "new" product designs for industrial use.)

That said, there are indeed some manufactures that make smooth and/or corrugated sheath MC that is suitable as an EGC. It can also be special ordered from a few that now make MC-HL almost exclusively. The manufactures can provide the necessary documentation and, if it is otherwise NRTL certified, I would tend to accept it.

2) Not unless the NRTL specifically required it. It isn't likely. If the MC sheath is recognized as an EGC in itself under UL 1569, the actual issue becomes the terminators. Basically that is the cumulative requirement of Sections 330.6 and Section 330.108 and its cross-references. [NEC 2017]

3) Yes, but it is probably recognized as ITC-HL. See Art 727. There are a few special rules for sealing shielded, twisted pairs/triads. See Section 501.15(D)(1); read the whole section carefully.

 

[lpfink]

Thank you Bob, I will read these sections again and continue my research. Appreciate your time on this!

I'm still waiting to hear back from our supplier of MC-HL as to whether or not this particular MC sheath is suitable as an EGC.

Loren

 

[rbalex]

Thank you Bob, I will read these sections again and continue my research. Appreciate your time on this!

I'm still waiting to hear back from our supplier of MC-HL as to whether or not this particular MC sheath is suitable as an EGC.

Loren

Just remember, if it is listed as MC-HL, it must have wire EGCs in the core. The sheath may be adequate as a stand alone, but you may have a difficult time convincing an AHJ.