Example: The nominal phase to neutral voltage of the network is 230 V and
the maximum disconnection time given by the graph in Figure F15 is 0.4 s.
The corresponding value of Ia can be read from the graph. Using the voltage (230 V)
and the current Ia, the complete loop impedance or the circuit loop impedance can
Ia, the complete loop impedance or the circuit loop impedance can
be calculated from
Zs
a a
= =
230
I I
or Zc 0.8
230 .. This impedance value mustt nevveerr bbee
exceeded and should preferably be substantially less to ensure satisfactory fuse
operation.