Interlocking means an arrangement between points, signals, and other appliances operated from a panel or lever frame, either electrical locking or mechanical locking or both, so that their operation must take place in proper sequence to ensure safety.
Key Principles:
- 1
It shall not be possible to take 'OFF' signals for a route unless all the points are correctly set and the facing points are locked for that route.
- 2
Once the signals are cleared, it shall not be possible to alter the points on the route unless the signals are put back to 'ON'.
- 3
Even though the signals are put back to 'ON', it shall not be possible to alter the points unless the intended movement over such points is completed.
- 4
It shall not be possible to operate signals leading to conflicting movements.
- 5
The points and signals can be operated only in a sequence to ensure safety.
- 6
Where signals are connected to any device, the signal shall not obey until the conditions for working such devices are fulfilled.
Standards of Interlocking
There are four revised standards of interlocking, viz., Std–I (R), II (R), III (R), and IV (R). The equipment of signals, mode of locking, and operation of points, signals, etc., vary in these different standards and they are as follows:
| Sl. No. | Item | Std I (R) | Std II (R) | Std III (R) | Std IV (R) |
|---|
| Allowable speed (KMPH) | Up to 50 | Up to 110 | Up to 140 | Up to 160 |
| 1 | Isolation | Not compulsory | Compulsory | Compulsory | Compulsory |
| 2 | TAS/MAS | TAS/MAS | TAS/MAS | MAS | MAS |
| 3 | Double Distant | Not compulsory | Desirable | Compulsory | Compulsory |
| 4 | Point operation | Mechanical | Mechanical/electrical | Mechanical/electrical | Electrical |
| 5 | Point locking | Key/Facing point/hand plunger | Facing point locking with point machine | Facing point locking with point machine | Clamp type Direct desirable |
| 6 | Interlocking | Key/mechanical | Mechanical/electrical/electronic | Mechanical/electrical/electronic | Electrical/electronic |