OP
steveberry11
Don't go down the TT route as you say the supply is at 400A I am guessing that it is some sort of factory with lots of machinery and associated equipment.
If an RCD trips you can import lots of hazards.
If the ZS value is high work out the R1 + R2 values from manufactures data add them to the ZE to determin if you do have a fault. if there is a fault repair it. If it is a case of a faulty joint on the SWA is that is due to poor workmanship. Check the resistance of all conductors from manufactures data. You can also check all conductors have the same resistance. Any odd readings may suggest that the line conductor joints may fail. You may have to remake the joints
If you are happy with the line conductors your customer may have to take the hit and excavate the cable and lay a new earthing conductor.
Asyou say the PIR 5 years ago was OK this may be a developing fault that you have found and not a cover up by the first contractor.
If an RCD trips you can import lots of hazards.
If the ZS value is high work out the R1 + R2 values from manufactures data add them to the ZE to determin if you do have a fault. if there is a fault repair it. If it is a case of a faulty joint on the SWA is that is due to poor workmanship. Check the resistance of all conductors from manufactures data. You can also check all conductors have the same resistance. Any odd readings may suggest that the line conductor joints may fail. You may have to remake the joints
If you are happy with the line conductors your customer may have to take the hit and excavate the cable and lay a new earthing conductor.
Asyou say the PIR 5 years ago was OK this may be a developing fault that you have found and not a cover up by the first contractor.
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