Hello,
You are just about there with the explosionproof definition. Explosionproof equipment is the heavy metal of the hazloc world as it must contain an explosion and quench any flame as the hot gases that escape. For that reason, the enclosures used are heavy, generally cast, and have very carefully machined faces, threads, or lips on covers that form this flame path. Another point to consider is that wiring methods require sealing very close (<18") from the enclosure or less if specified by the enclosure manufacturing to prevent pressure piling in the event of an internal "event".
NonIncendive by itself means that the equipment is incapable for creating a spark that would ignite a particular explosive atmosphere under NORMAL operating conditions. Because no faults are considered, it may only be used in Div. 2 applications for classes and material groups that it is marked for. There are no wiring methods associated with nonincendive as the unit must be pretty much self contained. That being said, Non-Incendive Field Wiring (NIFW) is like nonincendive, but does have wiring going to and from the equipment that is connected to other things. The signals on this wiring are not capable of generating an incendive spark in an atmosphere that it is approved for. Therefore ordinary location wiring methods can be used with NIFW. But remember: Div. 2 only (for the Class and material group that the equipment is marked for). And be sure to follow the equipment's control drawing to properly connect the NIFW connections!!! NIFW may have NIFW parameters that need to be verified to ensure two pieces of equipment are compatible and safe.
Intrinsically safe equipment is not capable of generating an incendive spark in the Class and material group it is marked even after two countable faults are applied to the equipment. Because of this degree of safety, IS is allowed in Div. 1 areas of the Class and material group that it was approved and marked for. If the equipment is self contained (handheld radio, etc) it is still considered IS, but obviously there is no wiring methods associated with it. For interconnecting IS, you have two classes of equipment: IS apparatus (located in the haz loc) and associated apparatus. Generally (and this point is also true for NIFW just substitute the word associated NIFW apparatus) you need to connect a device in the haz loc with something in the ordinary location. The device in the ordinary location that is approved to connect to an IS apparatus is the associated apparatus. Note that a lot of times, IS barriers must be located in an unclassified location, because they can be incendive in the event of a fault on the unclassified area wiring. However, it will prevent that energy from passing into the IS wiring. To connect up IS circuits, you must follow the control drawing of both the associated and IS apparatus to the letter! This drawing will also direct you to any calculations that you need to make to ensure suitable comparability of entity parameters. Sometimes, a system is approved as IS and there are no calculations required as long as the system is installed per the control drawing.
This was just a quick overview. There is a lot more to learn about NI and IS. I would encourage you to obtain and read UL/ISA 12.06.01 as a primer on IS. You can also apply this to NIFW as well.
Oh and yes, this rambling was only in context of Class/Div per NEC 501-504. Zones do not have NIFW or Explosionproof as a protection method. - Another topic for another day...
Cheers,
Bill
