Is an Arc-Flash Analysis valid if the gear isn't rated for the available short circuit current?

[McDaniel8402]

I've got a bit of an interesting situation on my hands. A customer has asked me to review a short circuit study performed by a 3rd party engineer. The "other guy" found that the customer's gear is rated at 65kA short circuit, but the available fault contributions (utility + in-plant motor backfeed) is about 75kA. So far, I can't find anything at all wrong with the report written by "the other guy". Obviously somebody failed to do a thorough study before this gear was spec'd, ordered, and installed.

Soooo, I'm fully expecting to have the customer request an arc-flash analysis, complete with a report and arc flash labels for this gear. I have absolutely no intentions of providing any such report or labels knowing that the gear is basically a bomb waiting to detonate in the event of a severe fault.

That said, I can't find anything to support my stance on the issue. I'm not sure if the arc-flash results would be valid if the gear is not rated for the available short circuit current. I'm no stranger to these studies, and I know the studies are examining two different issues (worker surviveability vs equipment surviveability), but the two are very much intertwined.

At this point, the issue of mitigation is a whole other story. I'm just looking for some document (OSHA, IEEE, NFPA, etc) which would corroborate my judgement call to refuse to give arc flash labels on gear that isn't rated for the available fault current.

Anybody got anything? Been in this spot before? Whatcha got?

 

[wbd]

I assume that the overdutied equipment is the main that is fed from the utilities transformer? If so, then the downstream equipment may still be able to be analyzed for incident energy. A couple thoughts on this:

1. When you use the term "gear" is that the switchboard/switchgear/panelboard rating or is it the installed breakers?
2. If it is the breakers causing the overdutied issue, have you checked to see if there is a series rating for these breakers?
3. If it is the buswork that is 65kA, you may want to contact the manufacturer as I have seen one manufacturer come out to the site and change the short circuit labels as the equipment was designed for higher but lower labels were used. (marketing I think)
4. Typically for arc flash the arcing current is much lower (for <1000V) than the bolted fault current so the arcing current may be within the rating of the breaker?
5. Are the motor loads realistic? For example: the motors were all lumped together for modeling purposes and assumed to be 100% on where in reality maybe only 75% are on at one time?
6. Are any motors on non-regen VFDs that may have been shown connected directly to bus?

 

[stevenal]

Perhaps IEEE 1584 section 4?