I want to calculate the size of the cable to be used for earthing for 11 kv having a short circuit current as

1) 25KA

2) Above 25KA

Can you e-mail the answer to my question as a table showing the size of earthing cable recommended?

 

Anonymous' 30-Nov (23:28) question needs clarification:

1) What does the 25-kA figure represent... the magnitude of a 3-phase fault, or a single-phase to earth-fault?

2) Is the 11-kV system neutral earthed? If so, is it solidly-earthed? Or is current restricted by installation of a neutral resistor?

3) To properly size a cable, current alone is insufficient! Many of its parameters must be known! What is conductor material: Cu; Al? Constuction type: 3x1/C; 1x3/C? Insulation material? Installation: in air; direct buried; in conduit (magnetic, non-magnetic, plastic, ceramic? Proximity to other cables? Non-sheathed? Magnetic or non-magnetic metal screen?

Please note the above items are only some of the particulars that must be known! And, there are a host of others. Other parameters include, but by no means limited to: ac and dc transients associated with the fault current; clearing time of the protective device, i.e., fuse or breaker!

Regards, Phil Corso ([email protected])