400V,
I can't say that I've ever installed a new sub-circuit, with Fault-Loop impedance solely in mind.
However, Voltage drop is always taken into account.
Regarding formulae, for calculating this,
I prefer to use this one:

Vd = lxIxVc
--------------
1000
Where l= Length of run(metres)
I= Circuit current(A)
Vc= mV drop per ampere-metre

There are also tables around for finding the voltage drop of a given length of run of a certain size of cable.
These are distributed by cable manufacturing companies.
Hope that this helps. [Linked Image]

[This message has been edited by Trumpy (edited 06-13-2003).]