×
Follow Us
Page 2 of 2 FirstFirst 12
Results 11 to 13 of 13

How do you calculate microhms from millivolt drop test?

 Jump to latest post
Page 2 of 2 FirstFirst 12
    #11
  1. STXERS17 is offline Junior Member Pro Subscriber
    Join Date
    Jul 2017
    Location
    South Texas
    Posts
    7
    Reputation
    Quote Originally Posted by SecondGen View Post
    I've seen this exact question. They are basically testing you on two fronts:

    1.) Can you calculate the value using ohms law?
    2.) Based on your experience, is this acceptable?

    250 micro-ohms is way to high for a 1600A breaker of any type. Test enough breakers and you will understand.

    You can usually find recommended values in circuit breaker instruction books, and if you compare them, you will find that they are all pretty similar. Here is an example from Square D:

    Attachment 195

    NW08 = 800A, NW12 = 1200A, etc.
    Great info, thanks.

  2. #12
  3. mattj77 is offline Junior Member Pro Subscriber
    Join Date
    Aug 2019
    Posts
    2
    Reputation
    15. You have performed a millivolt drop test on a 1600-ampere, low-voltage circuit breaker. The result is 25 millivolts at 100 amperes. What is the contact resistance, in micro-ohms, and is the value acceptable?
    Your Answer: 400 microhms; no
    Correct Answer: 250 microhms; no

    I'm not sure why my answer is wrong.

  4. #13
  5. Join Date
    Aug 2016
    Posts
    2
    Reputation
    Quote Originally Posted by mattj77 View Post
    15. You have performed a millivolt drop test on a 1600-ampere, low-voltage circuit breaker. The result is 25 millivolts at 100 amperes. What is the contact resistance, in micro-ohms, and is the value acceptable?
    Your Answer: 400 microhms; no
    Correct Answer: 250 microhms; no

    I'm not sure why my answer is wrong.
    You are applying Ohm's law incorrectly.
    V/R=A
    Solving for R
    V=R*A
    V/A=R
    .025V/100A=.00025 ohms

Page 2 of 2 FirstFirst 12
Subscribe

Share this thread

Related Topics

  1. AC millivolt test on battery banks
    By Machine Gun Kelly in forum Electrical Testing Talk
    Replies: 7
    Last Post: November 1, 2016, 10:10 PM
  2. Sizing equipment grounding conductors for voltage drop
    By testguy in forum Electrical Testing Talk
    Replies: 0
    Last Post: August 14, 2016, 05:04 PM
  3. Easy way to calculate transformer fault current
    By SecondGen in forum Electrical Testing Talk
    Replies: 0
    Last Post: June 11, 2015, 06:40 PM
  4. Calculate capacitor current knowing only V and C?
    By zofofg in forum NETA Level 2 Exam
    Replies: 2
    Last Post: February 26, 2015, 07:40 AM

Tags for this Thread

Follow us


Explore TestGuy


NETA Certification Training


NICET Electrical Power Testing


Help and Support




You are viewing the archives. Enjoy new features and join the conversation at wiki.testguy.net