Hazardous zones and grounding

[DigiMan]

Okay, I'm lost again with this one...

I got a question that said something like:
"In a class 1 div 1 location, what must be grounded?"
possible answers:
1) everything must ground ISOLATED
2) all permantly fixed, conductive surfaces must be grounded
3) all movable and non-movable surfaces must be grounded
4) any metal surface that can become charged must be grounded. (not sure about the wording of this last answer choice)

I found 501.30(a) that speaks of bonding, but nothing too specific. In 250.100 (bonding in hazardous locations), it only speaks of bonding non-current carrying metal parts being required to be bonded. I'm guessing it's answer #2... but im also deliberating with #3 -- all movable and non-movable surfaces and equipment must be grounded.

 

[rbalex]

This is a case where the exact wording of both the question and optional answers is probably necessary.

As a general rule, what must be grounded in a Classified location is the same as ordinary locations under Art 250. Sections 250.4(A)(2) and 250.4(B)(1) give the direction on what must be grounded for either Classified or ordinary locations. Sections 501.30 and 250.100 only restrict or mandate specific means and methods of grounding/bonding, but do not alter the targets.

 

[sgunsel]

As usual, it depends. If you are in a Class I area, static eletcricity can be a very real ignition hazard. Take a look at NFPA 77, Recommended Practice on Static Electricity. To prevent static electricity charge accumulation and subsequent discharge (sparks), ALL conductive objects, including personnel, must be grounded. Grounding for static dissipation requires a maximum resistance of one megohm(!). In special circumstances, such as operating rooms, minimum and maximum flooring surface resistances are specified. Explosives handling areas may also have specific requirements. Any fixed object that is conductive needs to be grounded. As the EC, you won't normally deal with personnel or portable apparatus, unless you are working in the classified area, but you may be required to provide grounding attachment points. That may or may not be part of your responsibility.

 

[rbalex]

As usual, it depends. ...

Boy is that ever true - which is why I wanted the exact question and answers.

For static electricity though the primary goal is bonding. Of course, if it is done correctly, eventually the bonds will also connect to a properly grounded surface. (Even if it weren't technically a "requirement," it's still the "nature of the beast")

This does bring up an ocassionally overlooked issue. As I mentioned in my original response, Sections 501.30 and 250.100 restrict or mandate specific means and methods of grounding/bonding. Understood properly, the goal is to insure that there is nothing in the effective ground-fault current path [250.4(A)(4)] or path for fault current [250.4(B)(4)] where even the smallest amount of fault current is required to jump a possible gap in a classified location. While it probably would not affect the operation of protective devices, the arc may still be sufficient to ignite a hazardous atmosphere.