Results 1 to 9 of 9

Thread: Earth fault loop impedance test above 100A

  1. #1
    Full Member
    Join Date
    Mar 2013
    Location
    Gauteng
    Posts
    86
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Earth fault loop impedance test above 100A

    Hi guys, would you guys agree with not using your loop tester to test at mains when its above 100A supply ? Cause ive heard that the earth fault loop impedance and PSSC test should only be carried out on installations with a main circuit breaker of 100A or less. For larger installations the value should be calculated. What if you don't have the values of the transformer etc to do the calculation?

  2. #2
    Email problem
    Join Date
    Nov 2016
    Location
    Umkomaas, KZN
    Posts
    5
    Thanks
    1
    Thanked 3 Times in 1 Post
    As far as I know its only PSC that must be calculated above 100A, earth loop impedance can still be tested above 100A.

    I have tested a 160A supply PSC with a meter, I had calculated the PSC and just wanted to check my calculations. I found that the meter overheated and the thermal cutout came in after testing the second phase. I would think on higher amp ratings you could damage the meter or worse have it catch fire or blow up in your hands while doing a PSC test at over 100A.

    Lionel.

  3. #3
    Full Member
    Join Date
    Mar 2013
    Location
    Gauteng
    Posts
    86
    Thanks
    0
    Thanked 0 Times in 0 Posts
    How would you go about calculating it?

  4. #4
    Bronze Member ACEsterhuizen's Avatar
    Join Date
    Mar 2012
    Location
    South Africa
    Posts
    151
    Thanks
    108
    Thanked 19 Times in 15 Posts
    Reg 8.5

    Click image for larger version. 

Name:	PssC Regs.jpg 
Views:	835 
Size:	44.6 KB 
ID:	6671

  5. #5
    Full Member
    Join Date
    Mar 2013
    Location
    Gauteng
    Posts
    86
    Thanks
    0
    Thanked 0 Times in 0 Posts
    I hoped there's another way cause I never have access to get the transformer vaulues needed for the calculation

  6. #6
    Silver Member
    Join Date
    Mar 2008
    Posts
    293
    Thanks
    5
    Thanked 45 Times in 38 Posts
    On most supplies its impossible to get to the transformer. I usually test after the first small breaker if I don't feel it safe to test directly at mains position.

    My meter, fluke 1653B, can test from 0 - 25kA. Its designed to handle such tests.

    Its pretty standard practice in most countries to test with a meter (well i can speak for the UK, Australia and New Zealand)

    If you are working with stuff with fault currents over 25kA then that is next level stuff. You must be practically working in the substation to get that kind of fault current.

    Fluke 1653B
    Computation: PFC or PSC determined by dividing measured mains voltage by measured loop (L-PE) resistance or line (L-N) resistance
    Range: 0 - 25 kA
    Resolution (Ik < 1000 A): 1 A
    Resolution (Ik >= 1000 A): 0.1 kA
    Accuracy: Determined by accuracy of loop resistance and mains voltage measurements.

  7. #7
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,874
    Thanks
    566
    Thanked 924 Times in 746 Posts
    All live tests can be dangerous and should only be done in conjunction with a risk assessment. That said, impedance testers are designed to accommodate overheating, it's expected and there's built in protection to prevent damage from occurring so I doubt the 100A live-test limit in the regs is motivated by the protecting the instrument.

    I still use my old Robin loop tester for determining PSC, it uses a 25A test current rather than the somewhat limp wristed 12A test the new fandangled Flukes use . If there's three phases to test it often gives the overheating warning on the third test if I do them in quick succession. No big drama, no explosions just the warning light comes on and it won't perform further tests until it's cooled down.

    If you can't calculate the PSC because of not having the transformer details you should be able to take the Ics rating of the suppliers MCB as an indication of the maximum possible PFC.
    _______________________________________________

    _______________________________________________

  8. #8
    Full Member W-TDMI's Avatar
    Join Date
    May 2013
    Location
    George
    Posts
    32
    Thanks
    1
    Thanked 4 Times in 4 Posts
    Quote Originally Posted by Pieter00 View Post
    I hoped there's another way cause I never have access to get the transformer vaulues needed for the calculation
    Do your LOOP impedance test and use the formula to calculate PSC if your tester is not capable of conducting such test.
    PSCC=V/Zloop 1PH
    PSCC=V/SQ3.Zloop 3PH

    V In both formulas is measured incoming voltage:
    V- 1Ph (P - N)
    V- 3Ph (P - P)

    Regards
    TDMI

  9. Thanks given for this post:

    Lionels (09-Mar-17)

  10. #9
    Site Caretaker Dave A's Avatar
    Join Date
    May 2006
    Location
    Durban, South Africa
    Posts
    22,296
    Thanks
    3,235
    Thanked 2,632 Times in 2,217 Posts
    Blog Entries
    12
    Quote Originally Posted by W-TDMI View Post
    Do your LOOP impedance test and use the formula to calculate PSC if your tester is not capable of conducting such test.
    The earth loop impedance test?

Similar Threads

  1. [Question] Loop Impedance
    By C-Cam in forum Electrical Contracting Industry Forum
    Replies: 6
    Last Post: 20-Jan-21, 03:00 PM
  2. Earth loop impedance testing
    By ians in forum Electrical Contracting Industry Forum
    Replies: 16
    Last Post: 24-Jan-19, 09:34 AM
  3. Domestic Earth Fault loop at mains position - convert to TNC-S?
    By skatingsparks in forum Electrical Contracting Industry Forum
    Replies: 2
    Last Post: 09-Jul-16, 11:49 AM
  4. Earth loop impedance and prospective short circuit (PSC)
    By mikilianis in forum Electrical Contracting Industry Forum
    Replies: 11
    Last Post: 21-Jan-16, 04:10 PM
  5. [Question] Earth Loop Impedance on COC test.
    By Jasond MIE in forum Electrical Contracting Industry Forum
    Replies: 8
    Last Post: 06-Mar-15, 01:42 PM

Did you like this article? Share it with your favourite social network.

Did you like this article? Share it with your favourite social network.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •