high zs reading advice please

[Farmelectrics]

an eicr was carried out to an industrial plant area were the zs readings were all high readings above the maximum for a tns installation i noticed that the supply cable in question was getting monitored by an elcb. However recently the company or contractors. have driven in earth rods local to the intake turning this into a TT install and the ze reading at the main db is now 15ohms which is acceptable for tt. My question is would you be happy with this, should there be labels indicating that this is a tt installation. interested to here your thoughts and advice. im told by the maintenance guys its been like this for years and the high reading was due to the fact that the separate cpc was stolen for scrap and was relying on the armour of the cable solely.

 

[westward10]

What was the Ze prior to the change to TT and is this a DNO supply or private.

 

[Farmelectrics]

its a private supply westward within the site its self the ze was 2.7ohms on the tns system. but obvisiouly all the readings from the outgoing circuits were high aswell and didnt meet there disconection times.

 

[Farmelectrics]

in a perfect world they should replace the separate cpc that was stolen and has caused this issue. however its at least a hundred metre run so there obviously trying to rectify this on the cheap just looking for reassurance that this is ok.

 

[westward10]

A 100m to the substation what is the line to neutral loop reading.

 

[Farmelectrics]

A 100m to the substation what is the line to neutral loop reading.

not aware that reading has been taken certainly not seen it anywhere on the test sheets. its had limitation on the ir tests so only ze/zs reading taken

 

[westward10]

The original 2.7 ohm says way too high even over 100m what size of cable is it.

 

[Farmelectrics]

it is high because the separate cpc was stolen for scrap. the cable i think is 4 core 185mm

 

[Farmelectrics]

my calculations at 100metres comes out at 0.33. however max zs value for 60947-2 is 0.36 as stated in the appendix of bs7671 so if the seperate cpc was still in the above would be the reading i think. my question is would you be happy with the 15ohm reading now its been converted to a tt system

 

[westward10]

15ohm is fine but i would be looking at why fault protection is not provided by the supply, something seems amiss with the earthing plus if the rcd is downstream what is protecting the incoming supply.