Zs ohms with maximum rcd ohms

[Wilson12]

If the maximum zs is okay up until 1667 ohms protected by a rcd why do we care about maximum disconnection times for the mcbs e.g why do we test and it's important to meet 1.37 or 1.1 zs on a 32 amp circuit

 

[Wilko]

The 80% factor is a good estimate of copper resistance at 70C when remeasured at 20C. So it's not a tolerance.
The BS7671 tabulated values will have the conductor temperature stated, and it's often 70C. We tend to test and measure when a circuit is at room temperature and so we multiply by 0.8 to get an equivalent value.

 

[Richard Burns]

The 80% factor is a good estimate of copper resistance at 70C when remeasured at 20C. So it's not a tolerance.
The BS7671 tabulated values will have the conductor temperature stated, and it's often 70C. We tend to test and measure when a circuit is at room temperature and so we multiply by 0.8 to get an equivalent value.

I think I have probably misinterpreted your words, but the proximity of the 80% appears to refer to correcting a measured resistance to a 70°C resistance.
Whereas it is the 70°C resistance that is multiplied by 0.8 to give an value close to the expected measured resistance at 20°C.
Or alternatively the resistance measured at 20°C is multiplied by 1.2 to give the expected resistance at 70°C

 

[Wilko]

... it is the 70°C resistance that is multiplied by 0.8 to give an value close to the expected measured resistance at 20°C...

Thanks - that's what I meant to say