help filling in condition report

Discussion in 'Electricians' Talk' started by AlexGoode, Feb 9, 2016.

  1. AlexGoode

    AlexGoode Member

    hi, I am an apprentice learning to do a bit of testing and am wondering if you could please help with a few boxes I am struggling with on a condition report as below.

    1.nature of supply parameters- taken at the board, can my prospective fault current be 587A( result given at same time as earth fault loop impedance)

    2.details of rcd main switch- difference between current rating( this time is 100A) and the 'fuse/device rating or setting'

    3.details of red main switch-cannot find the 'rated time delay'

    Thanks in advance
     
  2. Risteard

    Risteard Screwfix Select

    The result is given in kiloamperes, so you should record 0.59kA

    However don't do that because it isn't the Prospective Fault Current (PFC).

    Prospective Fault Current is the GREATER of the Prospective Earth Fault Current (PEFC) - which is what you have measured - and the Prospective Short Circuit Current (PSCC).

    It is PFC and not PEFC or PSCC which is to be recorded.

    The setting relates to an adjustable device.

    An S-type RCD to BS EN 61008 should operate within the time frame of 130mS to 500mS.
     
    FatHands likes this.
  3. spinlondon

    spinlondon Screwfix Select

    There are two currents that you have to measure.
    One is Prospective Earth Fault Current (PEFC), and the other is Prospective Short Circuit Current (PSCC).
    It is the greater of these that you note on the report.
    When conducting the PEFC test, you should have all bonding and earthing conductors re-connected.
    Many main switches are neither RCDs or MCBs. As such they do not trip.
    Some installations (such as where the earthing system is TT), use an up front RCD as the main switch. This is usually 100mA and time delayed.
    You only need to record the details of an RCD main switch, if one is installed.
     
    FatHands likes this.
  4. AlexGoode

    AlexGoode Member

    i thought that disconnecting the earth and applying the 3 leads would give me the z reading and prospective fault current reading, what is the difference between testing pscc and pefc?
     
  5. peter palmer

    peter palmer Screwfix Select

    The PFCC could be across either L-E (all bonding etc. connected) or L-N you record whatever is the highest reading, or it could be across phases if testing a 3 phase installation.

    Top tip : don't test across 2 phases with a single phase loop tester.
     
  6. peter palmer

    peter palmer Screwfix Select

    You do a Ze test with everything disconnected, this gives you a true reading of the incoming earth conductor. If you dont disconnect the bonding the main incoming earth could well be caput and you would never know it. Doing this test will give you a reading in amps as well but you normally never record it because with the bonding re-connected its almost always higher, or the L-N reading is higher.

    Actually its a good way to see if you have a TNS or TNCS supply, TNCS should give the same reading on the earth and neutral, if the earth reading is higher then its probably TNS.
     
  7. AlexGoode

    AlexGoode Member

    so i do the test with he main earth connected and then the same test without the earth connected is that right? and by only doing it dis connected i am probably recording the lower reading?
     
  8. spinlondon

    spinlondon Screwfix Select

    One you have completed the Ze test, you then reconnect all the earthing and bonding, and conduct a Zs test. Basically both the same.
    You then need to switch your tester to PSCC and may need to swap leads round.
    Obviously, I don't know what tester you are using, and don't know the markings on the switches or whether you are conducting a three or two lead test.

    To determine the PSCC for a 3 phase installation with a single phase tester, it is usual to test between each phase and neutral and the add the two highest values together. Some people just double the highest value.
     
  9. peter palmer

    peter palmer Screwfix Select

    One of the boxes on the cert asks for the Ze reading, you disconnect the main earth from the block/consumer unit, clip onto the main earth and do the test, you are looking for a reading in ohms, 0.35 say. You also take notice of the fault current in amps but only record the Ze on the cert.

    You then reconnect everything, make sure all bonding is in place and clip onto the main earth bar and repeat the test, the figure you are now looking for is the fault current (amps), this should be higher than the last reading in an ideal world (lower Ze reading but you dont need that). You then repeat the test again but this time on the neutral conductor instead of the earth. Whatever the greatest reading in amps you get between the 3 tests you record on the cert under "prospective fault current" or similar wording.

    Basically for PFC test you are trying to find out what the worst that can happen if there is a short right at the source of the supply and can the cut out fuse/sub fuse etc. handle it.
     
  10. AlexGoode

    AlexGoode Member

    thanks for the help, i did go through it with someone but after this discussion, there are a couple of uncertain areas. so my ze reading is with the earth disconnected and my zs at board is with the earth connected. is this right?
     
  11. Bazza-spark

    Bazza-spark Screwfix Select

    Spot on.

    Kind regards
     
  12. AlexGoode

    AlexGoode Member

    thanks, so will i take the highest current reading from these tests was the pfc?
     
  13. spinlondon

    spinlondon Screwfix Select

    Yes the highest value from the PEFC and PSCC tests is your PFC.
    This is required to ensure the withstand rating of equipment in the installation is satisfactory.
     
  14. peter palmer

    peter palmer Screwfix Select

    You can also use the reading in the adiabatic equation to look a smart **** in front of your assessor to explain why you have used a 10mm earth and not a 16mm
     
  15. AlexGoode

    AlexGoode Member

    Thanks for the replies, it takes a while but we get there haha
     

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