Need definitions RE NEC article 500 & NFPA 496-1998

[cryomark]

Item 1
NEC99 article 500 501-3 (b) (3)
In a class 1 div 2 environment, devices without make-break contacts, shall be provided with enclosures. "General- purpose-type enclosures shall be permitted."

Definition of general purpose enclosure?

We have a commercial 120V AC solenoid actuated vacuum valve whose coil is covered by a plastic case, preventing any incidental contact with energized parts. Does this qualify?

Item 2
NEC99 article 500 501-5 (b) (2) exception 3
"Conduit systems passing from an enclosure or room that is unclassified as a result of pressurization into a Class 1 Division 2location shall not require a seal at the boundary."

Need definition of "unclassified as a result of pressurization."

Our electrical/electronics enclosure is continuously purged and pressurized by dry N2. All potentially incendive outputs from this enclosure are interlocked by differential pressure sensing through the control system.

Does the state of pressurization turn this NEMA 4 enclosure into an unclassified enclosure?

 

[dpc]

Item 1 - NEMA 1 is General Purpose. Your solenoid valve may be OK provided that there are no contacts on the valve, such as for position indication.

Item 2 - I would say yes, but I believe an alarm output is required if pressurization fails.

 

[jsummerfield]

There are several classifications of enclosure purges. The type Z is the style that reclassifies the enclosure to permit unclassified equipment in an otherwise Division 2 area. The type X permits unclassified equipment in an otherwise Division 1 area. Type X requires the removal of all power upon purge failure. Type Z does not. There are purger duration times to remove hazardous before energizing the equipment, etc. Type Y is more like a type X and not frequently used. See ISA/NFPA 496 and vendor details pertaining to these purges. Requirements exist regarding gauge indication, restriction sizes, alarms, warning nameplates, temperature limits, etc. for the purge.

Perhaps one could even use a NEMA 1 enclosure but NEMA 4 is normally used. The solenoid valve with a plastic cover could qualify if installed within the properly purged enclosure. Also, the solenoid has no arcing contacts. Check with the manufacturer to see if it is suitable for Division 2 without the purge.


John