[Question] Earth Loop (Can it be achieved?)

[Neal]

Hi All

Need some help please.
I have a large customer that has had most of his earthing stolen.
The building has various 11kv substations that feed LV rooms that feed sub DB’s that feed consumer DB’s
The layout out does not allow for complete new copper earthing and neither does the budget. We have installed various earth bonding straps and used all the armouring strands that we can get our hands on. We have managed to get the Ze of the sub DBs down to 0.11 Ohms. (Main breaker off and new earth strap disconnected)
Now if we follow SANS
I have a Main breaker of 1250Amps
So calculate Ze = 240V/2(1250) = 0.096 Ohms.
I have tried many things including new copper earthing and I can NOT get it below the 0.1 Ohm mark.

Many thanks
Neal

[ians]

It wouldn't be chrome international by any chance?

[AndyD]

Can you maybe attach a drawing of your system layout? Is the LV main earth busbar bonded back to the main substation earth (are the HV and LV earths bonded)? What is the arrangement on the LV side (TN-S TN-C-S TN-C)?

Immediately I'm sceptical about achieving a sub0.1 ohm Ze using aluminum, what CSA have you specified and how did you come up with the requirement of 0.096ohms? Also how are you measuring your present Ze of 0.11ohms, what instrument and what proceedure are you using?