Blue Square Electrical Control System
E.P. Control Relay Panel
One was provided per power car, located on the underframe. "E.P." was the abbreviation for Electro-pnuematic.
The relay board was manufactered by J. Stone & Co. (Deptford) Ltd. but supplied by B.U.T.
Description
From the BUT 50000 Series Service Manual:
The E.P. control relay box contains an insulated panel on which are mounted thirteen Tonum type relays of three different specifications; the specification is stamped on a plate attached to each unit.
One relay (specification T3500) consists of one pair of normally closed main contacts. This unit is mounted horizontally so that the contact faces are in a vertical plane, thereby ensuring that they not collect dust.
Two relays (specification T3501) each consist of two pairs of normally open main contacts, in the centre of which is located one pair of normally open auxilliary arcing contacts. These are often referred to as the "sparking tips" and are accordingly arranged to "make" a fraction before and "break" a fraction after the main contacts.
The remaining ten relays (specification T3502) are similar to specification T3501, except that they only have one pair of normally open main contacts and one pair of normally open auxiliary contacts.
Schematic
This shows the connections to the panel, taken from the BUT 50000 Series Service Manual.