moisture in class 1 div1 enlosure

[a.bisnath]

In a class 1 div1 area , on a loading pier,a aluminium multi bolted box is getting a lot of condensing moisture the mating machined surfaces were sealed with silicone and it continued all cable glanding is from the bottom an are properly sealed the box has the controls and 480 volt contactors for a gangway winch the moisture has caused failures and blow outs across the phases .the failure has been catastrophic and it is the third time it has happened .May I ask the advice of the forum?

 

[kwired]

In a class 1 div1 area , on a loading pier,a aluminium multi bolted box is getting a lot of condensing moisture the mating machined surfaces were sealed with silicone and it continued all cable glanding is from the bottom an are properly sealed the box has the controls and 480 volt contactors for a gangway winch the moisture has caused failures and blow outs across the phases .the failure has been catastrophic and it is the third time it has happened .May I ask the advice of the forum?

They make "drains" to install in an unused opening in the bottom of the enclosure that are rated for the classification.

Sealing raceway threads or machined surfaces is considered a no-no in class 1 areas. It defeats some of the features of the system. When an explosion occurs within the system the pressure is relieved through the threads of raceways/fittings and through machined surfaces on covers. By the time any hot gases pass through these escape routes they have been cooled enough that they are not an ignition source for the outside environment. By sealing these items you compromise the design of the system.

 

[hardworkingstiff]

They make "drains" to install in an unused opening in the bottom of the enclosure that are rated for the classification.

Sealing raceway threads or machined surfaces is considered a no-no in class 1 areas. It defeats some of the features of the system. When an explosion occurs within the system the pressure is relieved through the threads of raceways/fittings and through machined surfaces on covers. By the time any hot gases pass through these escape routes they have been cooled enough that they are not an ignition source for the outside environment. By sealing these items you compromise the design of the system.

I agree with your post, but I do have a question. While your statement about the machined surface is 100% correct, do you think silicone would offer enough resistance to expanding gases to cause a problem? I don't, but I also acknowledge that it is not in compliance with the listing, and I would not seal the mating surfaces, but I might run a bead around the mating surface on the top and sides to divert water.

Do you think putting some moisture absorbing packets along with the x-proof drains would help mitigate the problems?

 

[rbalex]

This cut is for explosionproof breathers and drains. Used properly, they provide both ventilation and drainage. There are options, but enclosures prone to heavy condensation should use both ventilation and drainage.

The minor difference I would have with kwired is that silicon sealing on the machined surfaces and threads is a flat violation for the reasons he mentioned. A careful reading of the instructions that came with the enclosures, and very likely, labels in larger units should reveal that. The restrictions are also mentioned in the UL White Book. In addition, it messes up the grounding/bonding of the system.

 

[rbalex]

...
Do you think putting some moisture absorbing packets along with the x-proof drains would help mitigate the problems?

No, it just guarantees a maintenance problem when the desiccant saturates.

 

[a.bisnath]

moisture in enclosure

moisture in enclosure

I am happy for the replies given,originally, there was no silicone and the box had no problems,then,it started to leak hence the addition of the silicone between mating surfaces an also on the top across the two sides, the condensation continued, a synthetic grease was used between the faces that also did not help in the long run.The box did not come with a drain or xp fitting,I am thinking about a heater or purge air purge air would be difficult to do
A lot of the condensation is at the top of the box close to the line side of the contactors

 

[kwired]

I am happy for the replies given,originally, there was no silicone and the box had no problems,then,it started to leak hence the addition of the silicone between mating surfaces an also on the top across the two sides, the condensation continued, a synthetic grease was used between the faces that also did not help in the long run.The box did not come with a drain or xp fitting,I am thinking about a heater or purge air purge air would be difficult to do
A lot of the condensation is at the top of the box close to the line side of the contactors

The box and cover are not necessarily leaking, sounds like you are getting condensation from a top entering raceway.

But if you have contactors in there then you probably should have a sealing fitting within 18" so there shouldn't be all that much raceway to develop condensation either. Unless the raceway took time to fill with water above the seal and is now seeping slowly through the seal maybe?

 

[weressl]

I agree with your post, but I do have a question. While your statement about the machined surface is 100% correct, do you think silicone would offer enough resistance to expanding gases to cause a problem? I don't, but I also acknowledge that it is not in compliance with the listing, and I would not seal the mating surfaces, but I might run a bead around the mating surface on the top and sides to divert water.

Do you think putting some moisture absorbing packets along with the x-proof drains would help mitigate the problems?

Actually any kind of attempt to 'seal' the flanges and threads is counterproductive. Usually the water inside enclosures is the result of atmospheric moisture condensation and not rainwater or other direct water entry into the enclosures. Absorbent packages may work, but remember that each one of those designed to absorb a certain amount of moisture and after it is 'full' it stops 'working' and needs to be replaced. Space heater with a thermostat and surface temperature limited to the area classification T-rating may serve the purpose better.

 

[weressl]

I am happy for the replies given,originally, there was no silicone and the box had no problems,then,it started to leak hence the addition of the silicone between mating surfaces an also on the top across the two sides, the condensation continued, a synthetic grease was used between the faces that also did not help in the long run.The box did not come with a drain or xp fitting,I am thinking about a heater or purge air purge air would be difficult to do
A lot of the condensation is at the top of the box close to the line side of the contactors

The purge would defeat the XP purpose, if you're going to have a purged enclosure then construct it according to NFPA 496, it could be a NEMA 4(X) enclosure.

 

[weressl]

In addition, it messes up the grounding/bonding of the system.

The bolting itself will provide grounding continuity and even if you put Teflon tape over the thread it will maintain sufficient conductivity with the required number of threads engaged not to cause a problem. (The thread is designed to be self cutting/cleaning and will cut through grit and grime to assure metal-to-metal contact, even more strongly than the wiping action designed into contacts.)

 

[GoldDigger]

The bolting itself will provide grounding continuity and even if you put Teflon tape over the thread it will maintain sufficient conductivity with the required number of threads engaged not to cause a problem. (The thread is designed to be self cutting/cleaning and will cut through grit and grime to assure metal-to-metal contact, even more strongly than the wiping action designed into contacts.)

I have been told (and I believe) that the action of teflon tape on metal pipe threads is not to seal directly but to lubricate the threads so that you can more easily tighten them to the point of the metal deforming thread-to-thread contact that provides the actual seal.
That is indeed what also gives the electrical connection.

 

[weressl]

I have been told (and I believe) that the action of teflon tape on metal pipe threads is not to seal directly but to lubricate the threads so that you can more easily tighten them to the point of the metal deforming thread-to-thread contact that provides the actual seal.
That is indeed what also gives the electrical connection.

It is the metal-to-metal contact and the polymer filling the voids where is no contact that provides the seal.

 

[a.bisnath]

what is T-raring?

what is T-raring?

I do not know what is T-rating can someone send me a link or page so that I can follow this up?

 

[kwired]

I do not know what is T-rating can someone send me a link or page so that I can follow this up?

Temperature rating.

As used in the context where you are questioning would be referring to maximum safe temperature of the equipment before it becomes a potential ignition source for the classified location. This temperature will vary depending on what hazardous materials are involved.

 

[rbalex]

First, while PTFE (Teflon) tape may be UL listed; it isn?t listed for electrical purposes. TFE is recognized for certain insulation types, Type TFE for example [Table 310.104(A)]; but PTHE tapes have no recognized ?White Book? applications.

Second, CMP14 is paranoid about bonding/grounding. See the opening sentence of Section 500.8(E). As far as CMP14 is concerned, five threads, wrench tight, is both necessary and sufficient. While the Section doesn?t specifically prohibit PTFE tape, it is assumed that it is prohibited via Section 110.3(B) since PTFE tapes aren?t listed for such purposes. Remember, the ??Code is not intended as a design specification or an instruction manual for untrained persons.? [Section 90.3(C)] CMP14 relies on that a lot or Articles 500-516 would be a LOT longer.

A little history: If you look at any recent NEC Handbook relating to what is now Section 501.30(B), you will see the external bonding jumper run ?parallel? both physically and electrically. That was a result of a mid-90?s comment to an NECH photograph that showed the bonding jumper wrapped a few turns around the LMFC; i.e., it wasn?t ?parallel? in some inspectors? opinion. I made a Proposal to say ?parallel? simply meant the bond was ?electrically connected at both ends? of the LMFC. IMO a few wraps actually protects the bonding jumper physically from snagging. CMP14 rejected it on the basis that those few turns would increase the bond?s impedance ? that?s how paranoid they are.

Make a Proposal (Public Input) for the 2017 NEC to allow PTFE tape and see how it would fly.

 

[rbalex]

I do not know what is T-rating can someone send me a link or page so that I can follow this up?

In the NEC as referenced to classified locations, it is more properly a "T-Code" or "Temperature Class". See Sections 500.8(C)(4) and 500.8(D).

 

[weressl]

First, while PTFE (Teflon) tape may be UL listed; it isn?t listed for electrical purposes. TFE is recognized for certain insulation types, Type TFE for example [Table 310.104(A)]; but PTHE tapes have no recognized ?White Book? applications.

Second, CMP14 is paranoid about bonding/grounding. See the opening sentence of Section 500.8(E). As far as CMP14 is concerned, five threads, wrench tight, is both necessary and sufficient. While the Section doesn?t specifically prohibit PTFE tape, it is assumed that it is prohibited via Section 110.3(B) since PTFE tapes aren?t listed for such purposes. Remember, the ??Code is not intended as a design specification or an instruction manual for untrained persons.? [Section 90.3(C)] CMP14 relies on that a lot or Articles 500-516 would be a LOT longer.

A little history: If you look at any recent NEC Handbook relating to what is now Section 501.30(B), you will see the external bonding jumper run ?parallel? both physically and electrically. That was a result of a mid-90?s comment to an NECH photograph that showed the bonding jumper wrapped a few turns around the LMFC; i.e., it wasn?t ?parallel? in some inspectors? opinion. I made a Proposal to say ?parallel? simply meant the bond was ?electrically connected at both ends? of the LMFC. IMO a few wraps actually protects the bonding jumper physically from snagging. CMP14 rejected it on the basis that those few turns would increase the bond?s impedance ? that?s how paranoid they are.

Make a Proposal (Public Input) for the 2017 NEC to allow PTFE tape and see how it would fly.

No doubt that it is objectionable, I was just making the case that in practical terms neither the sealant between the flanges nor Teflon tape applied onto the threaded entry connections really reduce the grounding continuity of any electrical installation that maybe in those boxes, unless of course you have an 800A service disconnect:lol:.

I did make the case that from the prevention of condensation point of view BOTH above sealants are counterproductive, be their use permitted or otherwise.

 

[weressl]

I do not know what is T-rating can someone send me a link or page so that I can follow this up?

If you are not familiar with the T-Code, then I would suggest you have no business of asking ANY questions about installation requirements in Classified locations. It means that you have not read Article 500 or 501 or other from this series, that gives you the fundamental requirements of the NEC on those locations and (even then) you still should not call yourself proficient in electrical installation in Classified locations.

I am not trying to put you down, just to warn you about the seriousness of this business.

 

[kwired]

No doubt that it is objectionable, I was just making the case that in practical terms neither the sealant between the flanges nor Teflon tape applied onto the threaded entry connections really reduce the grounding continuity of any electrical installation that maybe in those boxes, unless of course you have an 800A service disconnect:lol:.

But you will not be running 1/2 raceway for an 800 amp circuit either, lots more thread surface area on what you will be running, so that evens the score some.