Could some one clarify the position on the tables to be used when assessing the actual zs readings against the max permissible in BS7671. The tables in the on site guide are obviously reduced by 20% to account for certain factors but the tables in 7671 do not have the formulae applied. When assessing the actual readings against the permissible and an assumption is made that the average ambient temp is within 10 > 20 OC could the 7671 table be used as the reference. I understand that although the NIEIC table within the front cover of the inspection pads is factored the inspectors do not recommend using that but refer you to the 7671 tables. I have an element of confusion here and would appreciate guidance on this matter.
Many thanks