2391 practicle advice please

Uptonelectrics · Sep 1, 2012

Hi, please i am studying for this and am starting to confuse myself,
1. Zs=Ze+(R1+R2) , (R1+R2) for radial and (R1+R2) for ring this I understand, but where do you get the R1+R2 for the distribution board (taking into acount that there are several circuits)
Live Tests
2.prospective earth fault current- remove main earth from MET and test on earth loop test against each phase incoming side of isolator - record highest reading. I believe this is correct.
3.prospective short circuit current - test between neutral and each phase record highest value and double record this on test sheet, I believe this is correct.
4.motor circuit - disconnect motor (R1+R2) on each phase or confirm continuety of conductors if on earth. if wired in SWA do you use the banjo/cable armour to do the R1+R2
Many thanks

telectrix · Sep 1, 2012

Uptonelectrics said:
Hi, please i am studying for this and am starting to confuse myself,
1. Zs=Ze+(R1+R2) , (R1+R2) for radial and (R1+R2) for ring this I understand, but where do you get the R1+R2 for the distribution board (taking into acount that there are several circuits). you don't. that is the Ze or Zdb for the board
Live Tests
2.prospective earth fault current- remove main earth from MET and test on earth loop test against each phase incoming side of isolator - record highest reading. I believe this is correct. no, you test Zewith earth dissed. PSCC with it connected to give the worst scenario.
3.prospective short circuit current - test between neutral and each phase record highest value and double record this on test sheet, I believe this is correct.
4.motor circuit - disconnect motor (R1+R2) on each phase or confirm continuety of conductors if on earth. if wired in SWA do you use the banjo/cable armour to do the R1+R2. if armour is used as cpc, then yes. if a earth conductor is used, then both are in the equation
Many thanks

my comments in red.

sparks1973 · Sep 1, 2012

Uptonelectrics said:
Hi, please i am studying for this and am starting to confuse myself,
1. Zs=Ze+(R1+R2) , (R1+R2) for radial and (R1+R2) for ring this I understand, but where do you get the R1+R2 for the distribution board (taking into acount that there are several circuits)
Live Tests
2.prospective earth fault current- remove main earth from MET and test on earth loop test against each phase incoming side of isolator - record highest reading. I believe this is correct.
3.prospective short circuit current - test between neutral and each phase record highest value and double record this on test sheet, I believe this is correct.
4.motor circuit - disconnect motor (R1+R2) on each phase or confirm continuety of conductors if on earth. if wired in SWA do you use the banjo/cable armour to do the R1+R2
Many thanks

1) if your on about the single phase sub board on the 2391 rig...then you would connect the line+earth/cpc on the sub cable at origin (3 phase panel)....and test between the 2 at the sub board....this would be R1+R2 for the sub...
2) correct...but dont forget to ask permission from the person ordering the test..or any other interested parties to isolate the supply (this would be the instructor)...safe isolation procedure and lock off....KEY IN POCKET...NOT LEFT ON THE TABLE...THEY WILL FAIL YOU FOR THIS......
3)you use the metal enclosure.....dont forget...an R1+R2 value you record should be the HIGHEST value aheaved....this would typically be between the line and an earthed metalic enclosure......such as a C/U...or panel....

plugsandsparks · Sep 1, 2012

Uptonelectrics said:
Hi, please i am studying for this and am starting to confuse myself,
1. Zs=Ze+(R1+R2) , (R1+R2) for radial and (R1+R2) for ring this I understand, but where do you get the R1+R2 for the distribution board (taking into acount that there are several circuits) R1 and R2 refer to cables, not DBs, you measure them, usually by connecting the live and earth together at one end and measure continuity between both legs together at the other end
Live Tests
2.prospective earth fault current- remove main earth from MET and test on earth loop test against each phase incoming side of isolator - record highest reading. I believe this is correct. nearly.. leave the earth on the MET
3.prospective short circuit current - test between neutral and each phase record highest value and double record this on test sheet, I believe this is correct. Nearly, only double for TP ccts, some meters measure L-L anyway so no need to double and can test L-L
4.motor circuit - disconnect motor (R1+R2) on each phase or confirm continuety of conductors if on earth. if wired in SWA do you use the banjo/cable armour to do the R1+R2 - same as any other cct, if SWA has earth core and its terminated in DB, use that. If its using the armourings - use that.
Many thanks