×
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

Step Potential

Step Potential

Step Potential

(OP)
Why does the tolerable step potential change with your soil parameters inside of ETAP?  I would have thought that your maximum allowable step potential would be fixed and independent from the soil parameters.  If my left foot is Va and my right foot is Vb, I am going to have (Va-Vb)/(resistance of me) current running through me. What am I missing?

RE: Step Potential

If the top layer of the soil that you are standing on has a very high resistance, such as if you put crushed rock on the surface of the soil, then you can allow for a higher earth potential difference between your feet - the additional resistance underneath your foot is saving you!

Test it for yourself in your ETAP, by increasing the resistivity of the surface layer of soil you will find that you tolerable step potential limit is increased.

RE: Step Potential

To meet the safe criteria, the surface voltage between the legs (Va-Vb), should be less than the allowable step voltage.

              Va-Vb < Estep

In accordance with the IEEE Std 80, the allowable step voltage for a 50 kg person standing in bare foot can be considered as follow:
                             
        Va-Vb < (1000+6Cs.ρs)x 0.116/√(tc)

For given fault clearing time (tc), the allowable voltage that a person can safely withstand is function exclusively of Cs and r

Cs = is the surface layer derating factor that account for the surface material thickness. As larger is the thickness larger will be the tolerable voltage

ρs= soil resistivity (Ω.m). As higher is the soil resistivity, the allowable voltage became larger.
         
(Ex. Crushed rock ~3000 Ω.m, asphalt 10,000 Ω.m)


 

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