×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Jobs

Ground Fault and Arc Flash

Ground Fault and Arc Flash

Ground Fault and Arc Flash

(OP)
The topic came up on another thread, so I'm posting a follow up here.  (http://www.eng-tips.com/viewthread.cfm?qid=199403&page=1)

The basic question is: Should ground fault protection be taken into account when performing an arc flash study?

Most (MOST, not all) arcing faults will propagate to 3 phase to ground faults, and will probably be taken out with the ground fault detection (if it exists). So, should this be taken into account when calculating trip times?

Currently, we do not look at this at our location, as I have yet to see anything on this, but it would make sense to use the ground fault clearing time.

RE: Ground Fault and Arc Flash

In enclosed equipment spaces, most faults start as line-to-ground but often escalate almost instantaneously to three-phase due to the ionized gases present.  Three-phase faults also result in the highest arc-flash levels.  

For these reasons, IEEE 1584 recommends that all arc-flash calculations be based on three-phase faults.  

Certainly ground fault protection can lower the risks associated with arcing faults (and impedance grounding can reduce it even further).  But unless you can lower the risk of  three-phase faults to a very low level, the PPE protection needs to be based on the worst case and that is three-phase faults.  

For outdoor equipment, with the much greater spacing between phases, three-phase faults are very uncommon and the new arc-flash requirements in the 2007 NESC are based on line-to-ground faults.  But inside equipment enclosures, it's a different story.

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!


Resources