Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


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

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

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

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?

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

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?

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

Perhaps IEEE 1584 section 4?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


White Paper - Considerations for choosing a 3D printing technology
The adoption of 3D printing into major companies’ product development life cycles is a testament to the technology’s incredible benefits to consumers, designers, engineers and manufacturers. While traditional production methods have limitations in manufacturability, 3D printing provides unparalleled design freedom due to the additive method of building parts layer by layer. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close