scope:

Those involved in the procurement, design and manufacture of track feed capacitor units used in conventional track circuits need to use this specification. It should be when procuring new / replacement track feed capacitor units used in conventional track circuits.

Note: The following two capacitor unit options are covered by this document:

a) An adjustable capacitor unit with five capacitors and an arrangement to put the capacitors IN or OUT of the circuit, giving a range of 1µF to 20µF in 1µF increments

b) A single capacitor unit with a one 20µF capacitor and an arrangement to put the capacitor IN or OUT of the circuit, giving either 20µF or open circuit.

Purpose

The purpose of this specification is to set out the London Underground (LU) requirements for the function and design of capacitor units for signalling track circuits.

Note: These units are used in safety critical signalling systems.