Page 416 - IRSEM_Main Book

18.3.4 Earthing

(a) A separate earth shall be provided for each instrument. The earth shall be
of an approved type and should be buried at a depth of not less than 1.5
meters and at a distance not less than 2.5 meters from any other earth. The
resistance of the earth should not be more than 10 ohms.

Note: Separate earth is applicable for only those equipments which work on earth
return. (This does not apply to block instruments which work on metallic return)
Also the protective earth for SPDs of block instruments to be connected to
common ring earth of Indoor Signalling system.

(b) The length of the Earth wire shall be as short as possible and cross section
of the wire not smaller than the size of the line wire and in any case shall
not be smaller than 4 mm dia. The earth wire shall not have a sharp bend
or spiral. Earth wire should be adequately protected from mechanical injury
and be efficiently connected to the earth. All connections to the earth shall
be well soldered.

Section 4: Installation of Single Line Token Instruments

18.4.1 (a) The Token instruments shall be so installed that the token of one section
can not be placed in any other instrument at that station. It is also desirable
that the installation be such that if the token is over carried, it can not be
placed in any instrument at the next station.

(b) Consecutive block sections shall be provided with tokens of configurations
A, B & C. Following block sections shall also be provided with similar
configuration in the same order. Where a junction station falls in between or
new crossing station is opened, tokens with special configuration (D&E)
shall be provided.

(c) Block Instruments must be mounted level (spirit level may be used) so that
tokens will not get into any particular race in case of ball Token instrument
and the token will not tilt in case of tablet type Token instrument.

18.4.2 Tests to be Conducted After Installation and Before Commissioning

(a) Check that correct polarities are connected to the instruments at both the
ends.

(b) Check that all mechanical parts are free to move without undue friction and
that there is no jamming of moving parts.

(c) Check that the commutator does not change unless the token gets into the
races in the case of Ball Token instruments and slides down the rail beyond
the tablet receiver in the case of Tablet Token instrument.

(d) Check that the insulation of electrical components and internal wiring of the
block instrument is proper and free from leakage from the instrument
body/earth.

Note: RDSO Booklet STS/E/BTI/IMI may be referred to for detailed instructions
regarding installation & testing.

Chapter 18: Block Instruments, BPAC & IBS Working Page 364 of 535