C1D1 Multiconductor Shielded Cable Seal

[lkdiaZ]

Spent all morning reading through posts reltated to this and since some are a few years old I thought I would refresh the issue.

Installing an explosion proof JB in C1D1 to serve as instrument junction box (terminations only). From the actual instrument to the JB it will be single pr or single triad shielded cables. From the JB to the Marshalling Cabinet (in a non hazardous area) it will be 24pr and 24 triad multiconductor with individual and overall shields. All cable will be in raceway 100% end to end. Trying to determine the best way with sealing the single pair and the multi pair cables end. From previous posts it seems that using an adhesive heat shrink such as 3m EPS300 has been done with success in other installs. Is this still the most economical way to go? I don't think I'll have issues with AHJ approval.


If we go this route, on the multi pair cable, do we have to apply the heat shrink over the overall jacket and then each individual pair? Does anyone have a picture or detail of an install using this method?

Any help is appreciated.

 

[petersonra]

I'm not real sure what it is you're describing but I don't think that you can replace a listed explosion proof seal with some adhesive heat shrink.

 

[don_resqcapt19]

I was going to answer this with the comment that seals may not be need based on 501.15(A)(1), but then I read 501.15(C) and that indicates that seals are always required for cables.
My guess is that since the cables are in raceways, that (A)(1) would apply, but not completely sure. (assuming that the raceway is one of those that are permitted by 501.10(A) for use in Class I, Division 1 locations.)

 

[lkdiaZ]

I'm not real sure what it is you're describing but I don't think that you can replace a listed explosion proof seal with some adhesive heat shrink.

Picture a multiconductor cable installed in a raceway. The space between the cable and the raceway needs to be sealed according to 501.15 (A) which is done with a sealing fitting and compound. Easy enough. However 501.15 (D) also requires to seal the inner part of the multiconductor cable, in other words, the voids between each of the conductors inside the multiconductor cable assembly. In particular I'm dealing with the exception in 501.15(D) (1) (shielded cables) and the exception in 501.15(D)(2) multiconductor cables. As per the exception this method does not necessarily have to be listed but it has to be approved. I've been searching everywhere for a product that will do this to no avail. In various threads of this forum there's mention of using an adhesive heat shrink that will seal the voids. Was hoping someone might have pictures and or better suggestion for this. We are using TC-ER multi conductor cable, in a rigid aluminum raceway. The cable is enclosed in a raceway or enclosure from beginning to end.

 

[lkdiaZ]

I was going to answer this with the comment that seals may not be need based on 501.15(A)(1), but then I read 501.15(C) and that indicates that seals are always required for cables.
My guess is that since the cables are in raceways, that (A)(1) would apply, but not completely sure. (assuming that the raceway is one of those that are permitted by 501.10(A) for use in Class I, Division 1 locations.)

Thanks for looking at this. See my response to petersonra for additional info.

 

[don_resqcapt19]

Thanks for looking at this. See my response to petersonra for additional info.

I still don't know if anything in the cable sealing subdivision applies where the cables are installed in a raceway.

 

[rbalex]

It is a circuitous route and I don’t have my NEC available at the moment to cite all the specifics; however, you have correctly identified that you need to seal the cable at the enclosure terminations. You’re also correct that shielded cables are not required to have the shield removed in order to seal the interstices.

So, how do you seal a multiconductor cable at the termination? Keep Information Notes 1and 2 of Section 501.15 in mind. Seals are only required to minimize not prevent the passage of gases and vapors. [IN No 1] Several methods are permitted to achieve this. [IN No 2] One way to seal the cable as described in Section 501.15(D)(2) by drawing the pairs/triads far enough back into the conduit seal to cover them and the jacket together. Another method is to use a shrink-on sleeve with a melting mastic inside around the end of the cable. Again the pairs/triads must be sealed with the jacket.

With regard to cables in conduit at boundaries, see Section 501.15(D)(3). Effectively, the multiconductor cable is treated as a single conductor if it is sealed properly at the terminations.

 

[rbalex]

This post has A poor illustration. I had a better one years ago but I’m not sure how to retrieve it

 

[tom baker]

I would lean towards the heat shrink, as I have used triad cables that are blk-wht, red-wht, blu- wht, and it’s easy to get the whites mixed up. Heat shrink would avoid that

 

[lkdiaZ]

This post has A poor illustration. I had a better one years ago but I’m not sure how to retrieve it

Thank you. I had seen that one in my search yesterday. So for a multiconductor 24 pr shielded cable I would install 24 heat shrinks around each pr and its shield and then another heat shrink over the outside jacket? Is that about right?

 

[lkdiaZ]

I would lean towards the heat shrink, as I have used triad cables that are blk-wht, red-wht, blu- wht, and it’s easy to get the whites mixed up. Heat shrink would avoid that

Thanks Tom - Any chance of pictures with the heat shrink? We don't do C1D1 that much but I'm surprised there isn't a canned method of doing this as this is a fairly typical install in the industrial world.

 

[petersonra]

One way to seal the cable as described in Section 501.15(D)(2) by drawing the pairs/triads far enough back into the conduit seal to cover them and the jacket together.

I think this is the only way I have seen shielded cables sealed.

Another method is to use a shrink-on sleeve with a melting mastic inside around the end of the cable. Again the pairs/triads must be sealed with the jacket.

I can't say I have ever seen this. But, my sample size is fairly small and generally only has cables with single pairs or triads in them. It would certainly seem easier especially when dealing with a bunch of pairs or triads in a cable.

OTOH, I can't say I ever looked all that close either. I always figured the guys doing it knew more about it than me.

 

[petersonra]

We don't do C1D1 that much but I'm surprised there isn't a canned method of doing this as this is a fairly typical install in the industrial world.

You might think so but the world of hazardous location wiring is full of such things.

 

[don_resqcapt19]

So I guess I have always done this wrong, as I have never done anything different for cables as compared to single conductors where there is complete conduit system installed for the cables.

 

[rbalex]

So I guess I have always done this wrong, as I have never done anything different for cables as compared to single conductors where there is complete conduit system installed for the cables.

The aforementioned INs have caused several AHJ misunderstandings. In my opinion, you haven’t done anything wrong since migrating gases/vapors through the interstices of multiconductor cables (and large conductors) is pretty much “minimized” in the first place. Nevertheless, the INs (especially No.2) scared enough AHJs that CMP14 scrambled to describe how to seal every conductor/cable construction we could think of, in raceway or not.

 

[lkdiaZ]

The aforementioned INs have caused several AHJ misunderstandings. In my opinion, you haven’t done anything wrong since migrating gases/vapors through the interstices of multiconductor cables (and large conductors) is pretty much “minimized” in the first place. Nevertheless, the INs (especially No.2) scared enough AHJs that CMP14 scrambled to describe how to seal every conductor/cable construction we could think of, in raceway or not.

In the case I described in the opening post of this thread, the application is a multiconductor TC-ER cable with individual twisted pairs shielded and overall shield complete in conduit end to end. On the hypothetical that inside the C1D1 boundary, and after the conduit seal, I let the cable come out of the conduit and enter the explosion proof junction box in free air. Is there a cable gland or termination that satisfies this requirement? I still don't see how this cable would be sealed even if it wasn't in conduit.

I'm still wrapping my head around the heat shrink. If I understand correctly, in a 24 pr cable we would have 24pr's of heat shrinks that would effectively prevent the gas to flow inside that particular twisted pr, but then you have the space between the twisted pairs which we have now made bigger in order to install the heat shrink by separating them which the code says we don't have to do. I'm wondering if putting a sleeve on every shield and pushing the cable assembly without the overall jacket a 1/4" or so back inside the conduit and then sealing it with a foam such as what polywater has doesn't do the trick. The problem is that we have to do something. Like rbalex said the mere construction of the cable probably (most likely) already takes care of the requirement but the code says we have to do something. Unless the AHJ agrees that by buying a cable such as TC-ER which has a gas tight sheath is doing something and sufficient.

Still hoping someone might have some pics of a similar install.

 

[rbalex]

You do not need an individual heat shrink for each pair or triad. Several heat shrink manufacturers have individual meltable mastic sleeves that may be applied to each one. Some slip on but most are split sleeves. After that an overall heat shrink with an internal melting mastic is then applied over the entire cable assembly.

 

[Hamid Bahrami]

can the outer jacket of the cable be stripped to where the end of the jacket would be submerged in the sealant (Chico) inside a Seal fitting?
this way the outer jacket is sealed, the conductors are sealed and the transition point from conductors to the outer jacket is sealed. Any migrating gasses would not be able to penetrate thru the cable core.
Actually, I don't see any other reasonable, cost-effective, and proper way.

 

[rbalex]

can the outer jacket of the cable be stripped to where the end of the jacket would be submerged in the sealant (Chico) inside a Seal fitting?
this way the outer jacket is sealed, the conductors are sealed and the transition point from conductors to the outer jacket is sealed. Any migrating gasses would not be able to penetrate thru the cable core.
Actually, I don't see any other reasonable, cost-effective, and proper way.

Technically, yes; however you will find it extremely difficult to do consistently. In Post #8 I referenced an illustration of my preferred method. I’ve used it successfully since the mid 1990s.