Ze testing

[martysparky]

I sit corrected, cheers mate, I don't know what I was thinking there.


I guess, it would include the parallel paths then.

 

[brucelee]

yes mate for pfc earthing conductor and all bonding in place which is good because the lower the value of the Ze the higher the current that will flow in the event of a fault so will allow enough current to blow the fuse/Cb quicker than the max disconnection times and with the earthing conductor and main protective conductors connected it will lower the value of the Ze because of the paralell paths from the extraneous conductive parts this is what we want more current the better and as long as the pfc is lower or equal to the breaking capacity of the protective device then it will operate correctly and if all your protective devices in the installation have a higher breaking capacity than the pfc then you only need to measure pfc at the origin
Pfc is always higher at the origin so this is the best place to measure and its the highest of the pefc and pscc value which is the PFC for single phase
for three phase measure all lines to Neutral seperatly and double the highest by 2 to get the three phase pfc

When measuring Ze you are checking to see there is actually a earth present and is sufficiently low enough to meet the maximum for the system to allow enough current to flow through to the star point at the transformer and back to your suppliers protective device ie cut out fuse and then through the consumers protective device ie CB to meet max disconnection times for Zs

when measuring Ze by disconnecting the earthing conductor from the MET and disconnecting the main protective bonding conductors will give you the true value of Ze without the paralell paths
and also to check it complies with the designers intentions