Referring again to Figure 4.7 and to the time sequence shown in Figure 4.8, a fault at the end
of the line should be cleared by Rd and CB4. Rcd sees the same fault as Rd and starts to close its
a factor of safety (X) (including overtravel, VV ). It is usual to add 0.3–0.5 s coordinating time to
the operating time of Rd which is calculated at its maximum fault. The same fault current is used
to determine the operating time of relay Rcd.