Hazardous equipment certification

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joshtrevino

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Location
Beaumont, TX
Before I state my question let me state a "for dummy's" definition of three hazardous area certifications. Please elaborate or tell me how inadequate my definitions are.

Explosion proof: The housing or enclosure is designed to contain any explosion.

Non-incendive: The device is designed to limit energy below levels that would cause an explosion with standard wiring???

Intrinsically Safe: Wired through an intrinsically safe barrier to limit energy below levels that would cause an explosion??? (Bonus: Does this require a calculation??? If yes, where is this calculation listed???)


After correcting my rudimentary definitions, please see actual question below:
If a transmitter is rated "FM IS, Non-incendive, and explosion proof" what does that mean? If the enclosure is explosion proof, why do I care if the transmitter is also IS and NI?

Please help!
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If the equipment is rated IS, it might allow you fewer restrictions on the wiring you connect it to.
Explosion proof, on the other hand, may put some restrictions on how you connect to it or attach it to maintain that rating.
 
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
 
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Oops, missed your real question at the end.

OK, somethings you need to apply more than one protection method to a product to use it in a haz loc. In this case of your transmitter, something inside the transmitter is capable of generating an incendive spark. So in order to locate the transmitter in the haz loc, it must use either a containment or exclusion protection method. Explosionproof is a containment protection method. At least one of the field wired circuits is IS or NIFW. These signals would not need to be wired using a Div. 1 or Div. 2 wiring method. So for this particular installation, it is very important to read the control drawing and follow all manufacturer installation instructions to the letter.

We also sometimes get multiple approvals on the same product like this transmitter (NI and IS). The NIFW approval is so you can install it in a Div. 2 location and connect it up to other NIFW apparatus. If you were to use IS in Div. 2, then the associated apparatus must be IS and have the 2 countable fault protection (expensive). Remember you can not connect IS to NIFW even in Div. 2! Where as if it is also approved for NIFW, then you can get away with either NIFW barrier (no faults) or use other compatible NIFW equipment. Just remember that you will either use IS OR NI, not both simultaneously.

Bill
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
If a transmitter is rated "FM IS, Non-incendive, and explosion proof" what does that mean? If the enclosure is explosion proof, why do I care if the transmitter is also IS and NI?

Please help!

Because that allows you to use any of the wiring methods allowed for XP, IS, and NI.

It is probably more cost effective for the manufacturer of such an instrument to get it rated all three ways rather than make three different versions of the same product.
 
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