Thank you for the guidance so far, unfortunately the previous EICR's carried out (by the company i now work for) simply put the maximum Zs as non verified and placed a limitation on the EICR, now that I have come in and started to source the actual maximum Zs figures its causing issues as circuits that should have likely failed previously but were passed are now failing. We were doing the testing on behalf of another contracting company who now need to explain the C2's to the client and feels allowing a 20% decrease in the maximum Zs is unfair, unfortunately knowing the operating current would require a thermal of all the conductors to be done and the more accurate factors allowed for at the time of test which has now passed. Although thermal imaging was carried out of the distribution boards as a whole and no conductors were noticeably sitting much above ambient at the time of test. 

The contracting company has asked since the incoming supply is greater than 230V (around 245v) can the measured voltage be used instead of the 230v nominal line to earth voltage as stated in the regs. The transformers on site are client owned. However i can see In ESQCR that unless specified in writing the voltage shall be assumed to be 230V. Would this therefore only be possible if the generator/distributor of the supply states it will be 245 and not change.

As much as id like to say accept the report, I am unfortunately now dealing with the incompetence of my predecessors who failed to verify these measurements on previous inspections. 

Thank you for the guidance so far, unfortunately the previous EICR's carried out (by the company i now work for) simply put the maximum Zs as non verified and placed a limitation on the EICR, now that I have come in and started to source the actual maximum Zs figures its causing issues as circuits that should have likely failed previously but were passed are now failing. We were doing the testing on behalf of another contracting company who now need to explain the C2's to the client and feels allowing a 20% decrease in the maximum Zs is unfair, unfortunately knowing the operating current would require a thermal of all the conductors to be done and the more accurate factors allowed for at the time of test which has now passed. Although thermal imaging was carried out of the distribution boards as a whole and no conductors were noticeably sitting much above ambient at the time of test. 

The contracting company has asked since the incoming supply is greater than 230V (around 245v) can the measured voltage be used instead of the 230v nominal line to earth voltage as stated in the regs. The transformers on site are client owned. However i can see In ESQCR that unless specified in writing the voltage shall be assumed to be 230V. Would this therefore only be possible if the generator/distributor of the supply states it will be 245 and not change.

As much as id like to say accept the report, I am unfortunately now dealing with the incompetence of my predecessors who failed to verify these measurements on previous inspections.