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Chapter 18: Block Instruments, BPAC & IBS Working

Section 1: Block Instruments General Requirements

18.1.1 General

(a) All block instruments shall be of robust construction and approved type only.

(b) On sections where AC voltages are induced due to power line parallelism,
suitable block instruments with appropriate protective measures shall be
provided as per Section.

(c) Block instruments shall normally be worked on physical conductors. Where
required, block instruments may also be worked on Radio/Optical Fibre
Cable with appropriate security features.

(d) Lightning Discharger: All Block instruments shall be provided with lightning
discharger to approved specification. Where a return line wire is used,
lightning discharger must be installed on both wires.

(e) Prevention of Irregular Operations: There shall not be any opening giving
access to the interior of the instrument through which it is possible to operate
the mechanism by any irregular means.

(f) Locking and Sealing Facilities: Facilities shall be provided for locking and
sealing the Block instruments. The doors of the Block instruments giving
access to the internal mechanism shall be provided with a double lock, the
key of one of which shall be in the custody of the Station Master on Duty
and the key of the other will be with the technician signal incharge of the
maintenance of Block Instruments. It shall not be possible to open the door
of the Block Instruments without the co-operation of both the agencies.

(g) Prevention of Unauthorized Operation: A lock or other device shall be
provided to enable the Station Master on duty to prevent unauthorized
manipulation of the instrument during his absence.

(h) Isolation of Telephone Circuit: Telephone instrument shall be provided in
conjunction with block instruments. It is desirable that the condenser or
other means provided for isolating the telephone circuit from the instrument
circuit is located within the instrument or in such a way as to be inaccessible
for outside interference.

(i) Bell Push: A Bell push button or a bell plunger shall be provided on the
instrument for exchange of bell codes.

(j) An isolated power supply (battery in standalone mode or DC-DC Converter
with isolated output) shall be used for line circuit for each block instrument.
This power supply shall only feed the block instrument and not any other
circuits. The power supply housing shall be locked and sealed if provided in
the SM’s Room.

Note: Where Integrated Power Supplies (IPS) are used for Block working, isolated
DC-DC convertor Modules shall be used for each Block separately.

(k) Tokenless Block Instruments worked on physical conductors shall be worked
on metallic return circuits.

Chapter 18: Block Instruments, BPAC & IBS Working Page 356 of 535