×
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

Arc Flash/Ground Fault

Arc Flash/Ground Fault

Arc Flash/Ground Fault

(OP)
Hi All,

While I'm still very much learning about this subject, as I look in the standard, there's no talk of ground fault settings for breakers.  Probably an ignorant question, but why?

Mike

RE: Arc Flash/Ground Fault

Mike,

In IEEE 1584, they state that three-phase faults should be used as the basis for arc-flash calculations.  There are a couple of reasons for this:

Arc-energy release for three-phase faults should be the worst case.  

Arcing faults that start as something tend to escalate (very quickly) to three-phase faults within equipment, due to the conductive plasma that forms.

So no matter what type of system grounding and ground fault protection you have, the PPE requirements are always based on the three-phase fault energy and phase protection (per IEEE 1584).  I don't think NFPA 70E really specifies this one way or the other.

For outdoor substations, with the much greater spacing between phases, these assumptions probably don't make much as much sense.  The Arc Pro software that is used by some utilties is based on line-to-ground faults, so I assume you can use the ground fault clearing times to determine the arc energy.  

RE: Arc Flash/Ground Fault

The proposed OSHA 1910.269 (generation, transmission and distribution) tabulated values (see http://mywebpages.comcast.net/dwallis2/subv.pdf) are based on line to ground faults, so the clearing times should be based on ground fault settings. Better yet, when performing live line work sacrifice coordination for safety and set the relay (selectable setting groups required) to trip instantaneously.  

RE: Arc Flash/Ground Fault

(OP)
dpc,

Thanks for that.

Mike

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