ABB RET650 Technical Manual page 258

Section 11
Secondary system supervision
252
The input signal DISCPOS is supposed to be connected via a terminal binary input to
the N.C. auxiliary contact of the line disconnector. The DISCPOS signal sets the
output signal BLKU in order to block the voltage related functions when the line
disconnector is open. The impedance protection function does not have to be affected
since there will be no line currents that can cause malfunction of the distance
protection.
1MRK 504 135-UEN A
Technical manual