Terminating at Motor Terminal Housing

[nollij]

This is kind of a complicated situation so I will explain it the best that I can.

We are doing a replacement in kind of cable to a very large amount of motors. Recently the inspector notified us that we needed to seal the cable as these motors are in a classified area (Class 1 Division 2).

From my understanding, 501.15(E)(3) states that we do not need seals as we are not terminating at an enclosure required to be explosionproof (article 501.15(E)(1)) or terminating at a pressurized location.

Our I/E inspector said that article 501.15(E)(1) exception no. 1 implies that we need a cable seal at the boundary. I believe that the scope of 501.15(E)(1) only applies to terminations and that the exception does not expand the scope of the section (probably just poorly worded).

I am currently trying to get the manufacturer to provide information to apply 501.15(E)(2) so that we can just avoid this entire mess.

Section 501.15(B)(2) exception no. 2 was also brought up. Does this imply that a conduit seal is required if the cable is routed in tray all the way back to a substation and then into conduit, even if the conduit is not at the boundary? This exception is vague on what part of the routing the boundary crossing is and thus makes an implication that even if the conduit routing is not across the boundary, a seal is still required.

Thanks.

 

[nollij]

I guess I should clarify what I am asking this forum:

Has anyone else had to seal a cable for a motor termination by an inspector?

Is the inspector's interpretation of the word "boundary" in the exception no. 1 for 501.15(E)(1) valid? I took it to mean the boundary of the enclosure or building located in a hazardous area but unclassified due to positive z-pressure. However, there is no definition to define what boundary means in the NEC and he is assuming it to mean the classification boundary.

Can anyone clarify exception no. 2 for 501.15(B)(2)?

 

[rbalex]

First, forget about 501.15(E)(2); there isn't a manufacture out there that will warrant that thier product won't transmit gases.

What are the conductor Types? Describe the full wiring method from motor terminal box to the source and including a discription at the boundaries.

 

[nollij]

First, forget about 501.15(E)(2); there isn't a manufacture out there that will warrant that thier product won't transmit gases.

What are the conductor Types? Describe the full wiring method from motor terminal box to the source and including a discription at the boundaries.

At a company next door to us, their cable manufacturer made the claim that their product won't transmit gases. They also rolled over and sealed the cable at the motor terminals anyway.

From the MCC the cable is either routed in conduit or tray to outside the substation. All of the routing is then on Tray for about a 100' where it then crosses the area classification boundary. It is routed to the individual motors on tray and dropped down from the tray to the motors in conduit. The average run length of cable is ~700'.

The manufacturer site lists the conductors (for the two types of cables used) as:
"Tin coated copper per ASTM B-33 Class B stranded per ASTM B-8"
"Bare, soft annealed copper per ASTM B-3, Class B stranded per ASTM B-8"

Also, our I/E inspector found a the section in "Electrical Installations in Hazardous Locations" by Peter Schram that describes the intent of section 501.15(E). In this case, I am correct in my assertion that the "boundary" referred to in the exception applies to the enclosure boundary and not the classification boundary. I guess now we just have to barrage the inspector with the facts and hope he doesn't pull the definition of "Approved".

 

[rbalex]

At a company next door to us, their cable manufacturer made the claim that their product won't transmit gases. ...

I'd like to have seen that one in writing.
I was actually asking if the cables were multiconductor, Type TC. They probably are since they are run in trays. If so, you are correct; they aren't required to be sealed at the terminations or the boundaries.

 

[dicklaxt]

We had quite a session on gases migrating the interstices of the cables one time years ago with a cable manufacturer..If I recall somewhere in the code it states the conditions where tests must meet certain conditions to be able to say the cable did not let gases migrate or such......The cable manufacturer admitted that under test conditions that could be achieved but after the cable is deformed thru pulling devices ie: rollers and pulleys all bets are off,at first glance on a cable spec it would appear that the cable is rated such when they say impervious to gas migration but they are really only talking about the sheath

We(design engineering firm) did however get a letter of liability release from a client when using such and such cable one time.I don't remember that cable or client.

dick

 

[rbalex]

The "basics" are described in 501.15(E)(2) - the one I said to forget. The problem is neither UL nor any manufacture can tell you what length is consistently good enough.

The "interstices" issue is created by one of the most perverse FPNs in the Code; i.e., 501.15 FPN No. 2. Here, there is absolutely no historical record that a problem actually exists; in fact, there isn't even any anecdotal evidence of a problem.

Edit Add: UL will certify Type TC (any amunufacture's) has a "gas/vaportight continuous sheath."

 

[bobgorno]

......Type TC. They probably are since they are run in trays. If so, you are correct; they aren't required to be sealed at the terminations or the boundaries.

I agree with nollij that 501.15(E)(1) is poorly written. The first sentence is clear...if the enclsoure is explosion proof a seal is required. You can infer explosion proof seal is intended. The second part seems to require a cable seal in the Div. 2 area regardless of the enclosure type (except for type Z purged). If there are no breaks in the cable jacket, then you can establish no other seals are required after that first seal.

I found the passage in the Scram and Earley book stating that no cable seals are required unless there is 6" WC pressure. This would be in concert with rbalex quote above and sure makes installs easier, but an inspector or system designer can, and often does, have a different interpretation based on the wording of (E)(1).

Sure would be nice to have the NEC written so that it was clearly understood by everyone.

Something to ponder.......
What if the motor is located outdoors and the indoor MCC is well ventilated? Granted, a 6" WC differential bewteen the location is hard to imagine. Do we need to have a mechanical engineer calcualte the ventilation pressure balance to prove to an inspector that passage of vapors is impossible?



Fun stuff.

BobG

 

[nollij]

Here is the section from the book that I mentioned in the 4th post:
"Even cables that have a core capable of transmitting gases or vapors in excess of the amount permitted for conduit seals are unlikely to transmit gases and vapors through the core unless there is a pressure differential between the end of the cable in the Division 2 location and the end of the cable in the nonhazardous location so as to force the gases and vapors through the core. The National Electrical Code recognizes this by indicating that a cable with a gas/vapor-tight jacket that is capable of transmitting gases or vapors through the cable core is not required to be sealed unless either it requires a seal because the cable enters an explosionproof enclosure, or the enclosure in the hazardous location is pressurized in such a manner as to subject the cable to a pressure in excess of 6 inches of water (1493 pascals, 0.2166 psi). In this respect, cables are not treated the same as insulated conductors in conduit."

Also, manufacturer's engineer reply to my request concerning 501.15(E)(2):
"The gas/vapor transmission rate or capability is also a mystery requirement. All multi-conductor cables are manufactured and assembled using various types of filler packing of the core, grounding conductors, binder tapes and lay-up of the core conductors. These cables are bent to varying degrees during installation and are trained in their final position assuming various bent configurations. All of this discussion points to the conclusion that all cables pass gas(excuse the pun). UL has not developed or requires any type of internal gas transmission rate tests. Manufacturer has not conducted any type of tests where we can say one test of one representative cable assembly represents all other assemblies."

 

[rbalex]

I guess my problem is I already understood what the Code means and didn't see how it might be misinterpreted. Having been a member of two different CMPs (including Panel 14) I can tell you it is a common myoptic issue. I still think it takes some tortured interpretation to think cables described in the OP need to be sealed.

I'll post a Proposal in the Proposal/Comment forum to clean up Subsection 501.15 after the 2011 NEC is issued. It won't be before 2014 that it gets published though, if ever.

 

[nollij]

A little update:

We all talked to the inspector today and it appears that he is starting to see it the way that we explained. He said that he would take the information we provided him back to the chief inspector and see what he says.

I guess we can only hope that he explains it to the chief inspector in the same vein that we explained it to him. Hopefully he remembers the main talking points and can convince him. We also provided him a copy of the book previously mentioned with important sections highlighted.

 

[nollij]

My optimism was unfounded it seems.

The inspector may agree that we do not have to seal if we have a continuous gas/vapor tight sheath after the evidence was presented. However, he does not feel we have a "continuous sheath" as we are not using a fitting to terminate the sheath of the Tray Cable. He does not consider a CGB as an acceptable fitting. There is nothing in the code defining "continuous sheath" or the proper way to pull out the conductors of the cable at the terminations.

He also agreed that the chances of gas passing through the core of the cable 700' or so to the MCC would be pretty much impossible. We would not be increasing safety by this at all.

At this point, the issue is being moved out of our hands and into management's. The inspector said that he was going to red tag our equipment soon.

 

[rbalex]

However, he does not feel we have a "continuous sheath" ...

He may not, but UL does. The latest version of the "White book" is available here. Do a search on category Code "QPOR" which covers "...Type TC power and control tray cable intended for use in accordance with Article 336 of ANSI/NFPA 70, ??National Electrical Code?? (NEC)." You will find the following UL statement:

Regarding cable seals outlined in Article 501 of the NEC, Type TC cable has a sheath which is considered to be gas/vapor tight but the cable has not been investigated for transmission of gases or vapors through its core.

​

 

[nollij]

The cable sheath is cut off and the conductors pulled to the motor terminals in the peckerhead. A couple of the motors have the sheath cut off in the conduit prior to the peckerhead.

The issue the inspector has is that we cut the sheath off the cable without using a fitting to terminate the sheath. Since we just cut the sheath off the cable to bring out the conductors he does not consider the cable to have a "continuous sheath."

At this point we are considering using TMCX fittings to terminate all of the Tray Cable at the peckerheads or into junction boxes.

 

[rbalex]

Permit me to caution you. TMCX fittings are only listed for MC/MC-HL cables. If a manufacturer tells you otherwise, ask for thier UL "e-number." At least one manufacturer is notorious for implying the suitability of their HAZLOC products for uses they aren't listed for.