pscc and pfc

[baza]

Hi everyone
Im fairly new to electrics and the forum, im looking for some help on testing of a PME supply, It is my understanding that because the neutral and earth are combined the psc and pfc should measure the same. (as told by my assessor from Elecsa) I have a pfc of 3ka and a pscc of 2.4kk. Im using a fluke multi purpose testor and wondering i if it is faulty. Many thanks in advance for any assistance

 

[scotsparky]

you sure you have a PME ststem? not a TNS

 

[bugsy]

Whats your Ze , when was your fluke last calibrated,

 

[baza]

hi Scotsparky

It has a large lable saying pme below the fuse carrier and the seal has previously been cut, which allowed me to see the combined neutral / earth connection

 

[baza]

Hi my fluke is 6 months old and the Ze is 0.11

 

[WayneL]

Hi Baza,

I wouldn't worry about it too much.

Firstly, your PSCC is Line to Neutral and, at 2.4 KA, gives an impedance of 0.096 ohms.

Your PEFC is Line to Earth and could include parallel paths through bonding of extraneous parts - at

3 KA this gives an impedance of 0.077 ohms.

A difference of approx 0.02 ohms - basically negligible and could be down to the bonding, leads,

connections.

Your Ze reading of 0.11 gives a fault current of approx 2.1 KA - but this is with the earthing conductor disconnected from the MET.
The difference in CSA of the tails and the earthing conductor could give the slight discrepancy in this reading


I wouldn't worry about it - just record the highest - the readings seem fine to me.

 

[trebor]

Hi everyone
Im fairly new to electrics and the forum, im looking for some help on testing of a PME supply, It is my understanding that because the neutral and earth are combined the psc and pfc should measure the same. (as told by my assessor from Elecsa) I have a pfc of 3ka and a pscc of 2.4kk. Im using a fluke multi purpose testor and wondering i if it is faulty. Many thanks in advance for any assistance

Exactly as WayneL says, pefc should be measured with the earthing conductor connected to gain the worst case comparison for your protective devices, if there are parallel earth paths then its going to be higher than pscc