Poor Zs

[stuart569]

Getting around 0.15ohms on a 400amp supply. It's a 4-core 240 and the run is about 120m. The spark at the job says he thinks the cable has been jointed twice due to being dug up and damaged. Its hrc cartridge link fuses. Had a squint around and reckon the max Zs is 0.09? Is this correct?

 

[IQ Electrical]

You are quite within your rights to use manufacturers data for maximum Zs values rather than the often much lower values tabulated in BS7671.

Also remember that with a site transformer in very close proximity, your Zs readings will be affected by the very low impedance and inductive reactance and that most earth fault loop impedance testers are only designed for circuits rated at around 50 Amps.

 

[steveberry11]

Not sure will find out soon enough

The reason I ask is that if it won't your efforts may be a waste of time if the installation was of a poor design and a EIC cover up.
Not sure if I would want a saw mill on an RCD
if the repairs will not address the loops on the other distribution boards one answer may be to re supply them from the main supply point. Not cheap but is one answer to the problem.