Page 496 - IRSEM_Main Book

21.1.12 Point Control Circuits

(a) The points once set shall remain in the last operated position until these
are operated by different route setting or by individual operation of points,
except when stipulated otherwise. However, isolation points of catch
siding, slip siding may operate automatically after the passage of train to
their isolation position where sectional route release is provided.

(b) Moreover, soon after CH/NX control is released, points shall not be
operated by route setting operation. However, the points can be operated
individually from the control panel/Control Terminal till such time the
CH/NX key is not inserted in point machine.

(c) Operation of points shall be possible only when the interlocking is free
and relevant point track circuit is clear. Emergency operations, where
provided when point zone track circuit fails, it shall be possible to operate
the concerned point provided interlocking is free by releasing an
emergency control. Each such operation shall be recorded on a counter.

(d) Interlocking between points shall be provided only to the minimum extent
necessary.

(e) Point control circuits shall be so designed that a cross connection or a
short circuit cannot operate a point or give a false indication of the same.

(f) Hand operated points shall be equipped with circuit controllers that are
operated by the switches when closed. Keys controlling such switches
shall be electrically locked by the approach track back locking track circuit
so that it's not possible to work them in the face of an approaching train.

(g) Means shall be provided to cut off the motor feed in case of obstruction to
the point movement after a predetermined time lag, based on the type of
point machine used.

(h) The point operating control circuits shall have track circuit control,
overload protection and cross protection.

21.1.13 Crank Handle & Siding Control Keys

(a) Crank handle/point NX key provided for manual operation of the points
worked by electric point machine must be interlocked with signals.

(b) The crank handles shall be provided to facilitate operation of points in
case of failure of point machines. For this purpose, if necessary, the
points in the yard may be divided into convenient groups and to
distinguish particular groups, crank handles with different wards shall be
used. The crank handles shall, however, normally be locked. It shall be
possible to release them for use in point machine by releasing a control
from the control panel. With the crank handle released, it shall not be
possible to clear the signal for the concerned routes. The interlocking of
crank handle can also be achieved by using NX key of different wards.

Chapter 21: Relay & Electronic Interlocking Page 442 of 535