Ring Main

The problem can only be solved by local observations and testing.

As said by #1, observation of the site/fault will be essential to solve the question.

Also, the over-current will operate first if the fault condition to earth was not happening quicker and first:

if the cable damage happened in a way that the conductors shorted 1st, before the path to earth was fully established, then the over-current will trigger 1st. Then the earth fault would not have materialized.

Just a possibility...

Dear Mr.Lucke,

Thanks for your reply. I have one more doubt. How the EFI indicator connected to the cable?. Will it operate during phase fault???.

Rgds

Byju

EFI = Earth Fault Indicator ?

If yes, in your question you seem to have said that this did not operate! (Or I did not understand your english properly). I don't have a diagram of the connection of this EFI but as its definition suggests, it must be connected on the earth return line to detect an earth fault current only. Phase to phase fault will not normally trigger it unless the same fault produced an earth leakage current at the same time.

I assume the wiring is correct. Earth fault & EFI has a different CT (different input current) respectively.

Check the Current Transformer for Earth Fault. Is it Residual Connection or Current Balance Current transformer.

Please check the Over Current Relay and Earth fault current ampere setting and time setting. If the OCR time setting is faster than Earth fault protection, then the earth fault wil not operate because the fault already cleared by OCR.

If your EFI and earthfault has the same input current and the same relay please disobey this information, then the problem is in the relay.