Using Cable Glands in Class I Zone 2

[HSB_007]

Good day everyone
I need your help to better understand the requirements for using cable glands for enclosures located in class 1 zone 2. We have a requirement for the junction box (enclosure) to be only NEMA 4X since the enclosure has only terminal blocks (wire terminations). We also require cable glands to be EX d. I am NOT so sure why we are requiring cable glands to be Ex d.

I am trying to optimize the cost of the installation by removing the requirements of this cable gland to be Ex d. Instead, I would think that a cable gland which ensures the same ingress protection would be enough to make sure the same NEMA 4X is maintained (IP 66).

1- Are there cable glands which are just NEMA 4x (or IP66)? Does the NEC specify those types?
2- Would be a good idea to use GRP (Glass Re-enforced Plastic) enclosure with GRP cable glands to further optimize the cost since we currently require boxes to be 316SS? Is it a bad idea to use GRP box but with aluminum or brass cable glands as I am suspecting the GRP glands may fail since they are not strong enough?

Thank you for your valuable feedback.

Have a great day!!

 

[rbalex]

Trying to mix/match NEC Zones with IEC Zones is very difficult. They just aren't the same no matter how much ISA has tried to force-fit them. I co-authored a paper on the subject. (Note the IEEE copyright permits personal use of the paper.) It's dated now because it doesn't address the ATEX Directive, but the salient points are still valid even after nearly 20 years.

I would agree that "Ex d" glands are overkill in Zone 2 for either NEC or IEC where the enclosure is only required to be NEMA 4X.

The question is, "Which set of standards are you trying to comply with, NEC or IEC?"

 

[Smart $]

...
The question is, "Which set of standards are you trying to comply with, NEC or IEC?"

This seems to be the major issue in a lot of HL assessments nowadays. Many seem to forget or are unaware the answer may be dictated by law.

 

[HSB_007]

Cable Glands reply to Robert

Cable Glands reply to Robert

Thank you Robert for your quick reply.

We allow NEC and IEC standards. Though, in this particular case, I am trying to follow the NEC.

Is it just easier to use nickel-plated brass Ex d gland to be used either with 316SS or GRP boxes? I am told yes. I would like your valuable feedback.

Another question if I may ( I know it has nothing to do with Glands):
As part of the optimization process to reduce costs "while achieving the same system reliability", I am thinking to allow mixing of signal types within the same multi-pair cable. We currently mandate using one multi-pair cable for each signal type (within the same signal level. For example, if we are using 4-20 ma DC signals, then you could not mix 4-20 ma DC signals with (say) level switches or other similar signal types. I believe this is a waste of $$ since the multi-par cable has individually shielded pairs. What is your take on that? Do you know of any document which specifically allow doing that. I thought there was an IEEE document which allows that, but I could not find it.

Thank you gentlemen for your outstanding help. I really love this site and think highly of it and highly of you all for the great help and support you do to your fellow friends all over the world.

 

[rbalex]

Thank you Robert for your quick reply.

We allow NEC and IEC standards. Though, in this particular case, I am trying to follow the NEC.

Is it just easier to use nickel-plated brass Ex d gland to be used either with 316SS or GRP boxes? I am told yes. I would like your valuable feedback.

Another question if I may ( I know it has nothing to do with Glands):
As part of the optimization process to reduce costs "while achieving the same system reliability", I am thinking to allow mixing of signal types within the same multi-pair cable. We currently mandate using one multi-pair cable for each signal type (within the same signal level. For example, if we are using 4-20 ma DC signals, then you could not mix 4-20 ma DC signals with (say) level switches or other similar signal types. I believe this is a waste of $$ since the multi-par cable has individually shielded pairs. What is your take on that? Do you know of any document which specifically allow doing that. I thought there was an IEEE document which allows that, but I could not find it.

Thank you gentlemen for your outstanding help. I really love this site and think highly of it and highly of you all for the great help and support you do to your fellow friends all over the world.

Then the next question, "NEC Divisions or Zones?" They don't mix and match all that well either. It can certainly be done, but you definitely need to know what you're doing.

 

[rbalex]

I suppose I can still address the second question.

Most likely you're dealing with Class 2 and/or 3 wiring subject to Article 725. Originally, and as acknowledged in Section 725.2 Definitions, Class 2 and 3 circuits were less subject to fire and/or shock hazards and some of the Chapter 3 wiring restrictions were reduced. However, as the telecommunications, information technology, and control systems industries gained influence on this Article, signal protection became the actual ultimate concern.

That said, while electrical safety may not be a particular concern, reliability is. Personally, I don't recommend switched circuits to be in close proximity to 0-20ma circuits. It may not be inherently dangerous but it isn't demonstrably reliable either - you just don't know; it may work, but you can't count on it.

Edit add: IEEE, ISA and API all have separation recommendations. None of them would recommend combining signals as economically justifiable.