Results 1 to 5 of 5

Expected contact resistance measurement based on breaker frame size

  1. SecondGen's Avatar
    SecondGen is offline
    I push buttons.
    NETA Level III
    Join Date
    Jan 2014
    United States

    Expected contact resistance measurement based on breaker frame size

    Here is a pop quiz: What is the expected contact-resistance measurement for a 4000A 480V air circuit breaker in good condition?

    This question might be confusing to some technicians because there has been very little written on the subject and contact resistance readings in the field are often all over the place.

    Manufacturers will occasionally recommend values in their literature, but not often. The universal rule of thumb for contact resistance has often been to get it as low as possible and as even as possible between each phase. The higher the frame size, the lower the contact resistance readings should be.

    While this may be good advice, it does not reveal any underlying problems with the breakerís lubrication or contact pressure.

    Jim White has written about this in the Summer 2007 issue of NETA world. In his article titled ďCritical Maintenance for Circuit Breakers,Ē he says the expected contact resistance of a 4000 ampere 480 volt circuit breaker should have a reading of something less than 30 microhms. White says smaller breakers may have readings of 60 to 80 microhms, with molded case breakers having contact resistance readings in the hundreds of microhms.

    This criteria is based on the ampere rating of the breaker rather than its voltage rating, White says. For example, a 2000 ampere medium-voltage circuit breaker will exhibit similar contact resistance to a 2000 ampere low-voltage breaker.

    An experienced maintenance group knows the normal average contact resistance for a given size circuit breaker, according to White. A value somewhat higher than that average may indicate that the lubricant is beginning to dry out but hasnít reached the problem plateau yet. The important part of this is to perform the test annually and trend the changes.

    So there you have it, I have attached the entire article if anyone is interested in learning more circuit breaker maintenance techniques. Itís a good read.
    Reply to Post • 
    Attached Files Attached Files

  2. #2
  3. Join Date
    Jan 2015

    contact resistance of circuit breaker

    Read the article, it was very informative. Some points where known but others were new.
    Reply to Post • 

  4. #3
  5. Join Date
    Jan 2015
    good article. thank you
    Reply to Post • 

  6. #4
  7. Join Date
    Jun 2015
    agreed, good info.
    Reply to Post • 

  8. #5
  9. Join Date
    Apr 2015
    Milwaukee, WI

    Good Article

    Good article. I'm aware from experience where most breakers should come in, but wasn't aware that Jim White had an article out on this.

    Reply to Post • 

Login or register to leave a reply!

Related Topics

  1. Easiest method of determining contact sequence
    By lester mcmanaway in forum NETA Level 3 Exam
    Replies: 10
    Last Post: December 8, 2016, 06:34 PM
  2. Replies: 5
    Last Post: November 18, 2016, 09:36 AM
  3. How to Size Transformer Neutral Resistor
    By AlexT90 in forum NETA Level 3 Exam
    Replies: 3
    Last Post: April 12, 2016, 03:04 PM
  4. Replies: 11
    Last Post: March 31, 2016, 02:26 PM
  5. Schneider Electric Recalls Square D-Brand F and K Frame Circuit Breakers
    By veracon0700 in forum Safety and Arc-Flash Talk
    Replies: 0
    Last Post: December 4, 2014, 02:05 PM

Related Content

Tags for this Thread

Search TestGuy
   Tag Cloud   Advanced Search
Follow us

Explore TestGuy

NETA Certification Training

Help and Support