×
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

Parallel cable impedance

Parallel cable impedance

Parallel cable impedance

(OP)
In the IEEE Buff Book (ANSI/IEEE std 242-1986) more specifically page 94, figure 21 shows the basic formula for calculating parallel impedance.

Z= (R1+jX1)*(R2+jX2)/(R1+jX1)+(R2+jX2)

If you substitute some simple whole numbers for the values such as R=2 and X=2 (for ease of calculation) the resulting impedance is

Z= 1/2 +j1

This illustrates that the resistance value is divided by the number of conductors (in this case 2) and the reactance value of 2 parallel cables is the reactance value of the one cable.

In the Buff Book on the next page 96, however, there appears a contradiction in the example where it shows the reactance value being divided by 2 for paralleled cable.

I must be missing some basic understanding here. Can anyone explain the difference?

The basic question is: What do you do with the reactance component for paralleled cables?

The calculation is being used for fault current and voltage drop.

RE: Parallel cable impedance

Do your math again.  I used R=2 and X=2 and came up with the parallel combination of Z=1 +j1 which is correct.  Be careful of all the j^2 terms in the equation - don't forget that j^2 is -1.

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