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This specification relates to design requirements for a miniature tractive armature line relay of the plug-in type for use in 110v signalling circuits, incorporating a rectifier feed unit, and suitable for use with 110v 25w lamps. It is intended to be used without an external resistor and with a lamp circuit having characteristics such that under extreme variations of lamp consumption and supply voltage the line currents will meet the operating values specified in Clause 18.2. The relay will operate with four lamps burning and will release with only two lamps burning. The relay shall not make front contacts when two cold lamps are switched on.