Touchscreen HMI in a Class II Division 1 Group EFG Hazardous Location

[rekjr_mgs]

Working on a new piece of equipment that will go into a Class II Division 1 Group EFG Hazardous Location. The previous non-HL unit that this new one is based on had an A-B PanelView 1000. We'd like to stick with this solution since the program is already written but are getting conflicting info back from A-B re: the suitability of this unit to the environment. We are planning on putting it in the door of a non XP enclosure (NEMA ??) with a P&F type Z purge unit. If it matters, this enclosure is separate from the main electrical enclosure and should only contain the 24VDC HMI and perhaps some Intrisically Safe pushbuttons. On one hand A-B says it is rated for the purge pressure but can't seem to confirm whether it still will meet Class II Div 1 when installed as specified. Anyone with experience similar to this for this environment? Does it make sense that, while a device that is mounted to the exterior skin of a purged enclosure can tolerate the pressure, it still does not actually meet the appropriate spec? Thanks in advance for the help!

 

[rbalex]

A few thoughts first:

1. How do you anticipate Type Z pressurizing being effective in a Division 1 environment? It only ?Reduces the classification within the protected enclosure from Division 2 or Zone 2 to unclassified.? [NFPA 496, Section 3.3.8.3]
2. Do you really have Group E; which can only be Division 1? [NEC Section 500.5(C)(1)(3)]

 

[rekjr_mgs]

Thank you for your response rbalex.

1. I will take this back to my vendor who quoted the enclosure/purge system. I suspect it should be a Type X.
2. My customer specified the Groups E, F and G - and yes, it is in a Div 1 environment. I'm not sure I understand your point. Please clarify.

Any further feedback is greatly appreciated!

 

[rbalex]

I obviously don't know the processes involved, but it?s difficult to imagine a location where all three Class II Groups are present. Group E is automatically Division 1.

That said, if Division 1 is indeed involved, you have a problem. Unless you are using an Intrinsically Safe system, there won?t be any acceptable ?ordinary location? enclosures available. See Section 502.10(A)(1)(4). Pressurizing (of any Type) only deals with the conditions inside the enclosure and Class II is actually more concerned with the enclosure's external surface temperature and accumulations of surface ignitible materials.

If you can justify Division 2 and establish a proper ?T ? rating?, you won?t need pressurizing at all and dusttight enclosures are suitable.

 

[rekjr_mgs]

Yes - definitely a Div 1 Group E environment.

We will be using IS field devices (photoeyes, proxes, valves, etc) with the appropriate barriers in the purged main enclosure. The purged HMI enclosure will likely have only the HMI unit - we'll put the operator PBs in an adjacent XP PB station box. I am now getting feedback from our enclosure people that adding an additional door with a clear panel over the HMI may be the solution. The area behind this door will be pressurized under normal running conditions. When the HMI needs to be accessed the clear panel door is opened and the purge unit begins cycling to (attempt to) maintain the pressurization. I am awaiting feedback on this solution - not sure if there is a potential timeout situation if you leave the door open too long.

Any comments on this possible solution are appreciated.

 

[rbalex]

Group E scares me .

Be careful about using explosionproof enclosures. See Sections 502.5 and 502.10(A)(1)(4).

Sealing is probably to only maintain pressure. See Section 502.15 and note there?s virtually no difference between Class II, Division 1 an 2. Also note this is an ?X-pressurization? application.

Otherwise, as I understand your description, it sounds ?suitable.? See Section 500.8(A).

 

[weressl]

I obviously don't know the processes involved, but it?s difficult to imagine a location where all three Class II Groups are present. Group E is automatically Division 1.

That said, if Division 1 is indeed involved, you have a problem. Unless you are using an Intrinsically Safe system, there won?t be any acceptable ?ordinary location? enclosures available. See Section 502.10(A)(1)(4). Pressurizing (of any Type) only deals with the conditions inside the enclosure and Class II is actually more concerned with the enclosure's external surface temperature and accumulations of surface ignitible materials.

If you can justify Division 2 and establish a proper ?T ? rating?, you won?t need pressurizing at all and dusttight enclosures are suitable.

You can add a surface fresh air-wash surrounding the screen that would prevent an ignitable concentration to become in contact with the touchable surface, which is what - I guess - Bobs concern is. In essence you would 'create' a non-classified area in front of the screen.

 

[rekjr_mgs]

I just rec'd a spec from my customer that corroborated my previous post along with some incidental details. I am going to run this solution by my NRTL for confirmation but just wanted to close the loop with the forum. I'll post any followup info as needed. Thanks to all for your help!