Zs, R1+R2 Measured Values?

[IQ Electrical]

Hypothetical question here

If you did measure the Zs and it was within tolerance and later one of the parallel paths was removed i.e. An extension was built and the incoming water pipe was changed to plastic, then how would you ensure that the Zs value was still within tolerence.

I know that at the time of install it was ok and you cant foresee every future change but surely it is better to ensure that the individual circuit Zs ( by calculation ) is within tolerance.

I see your point but remember that BS7671 values even after correction have large tolerances built in-as an exercise, ask Wylex etc for their manufacturers max Zs ratings (which you are quite entitled to use)

There's a surprisingly large difference.