Type B Vital Relays - Alstom

Theory of Operation
2.2. RELAY CONTACTS AND COILS
2.2.1. Definitions
The following terms are used in the descriptions of how relay contacts operate:
• Front -Relay contact that is open when relay is de-energized.
• Heel - Contact that is driven by pusher.
• Back - Relay contact that is made when relay is de-energized (normally closed).
• Make - Specified dimension that will cause all front or back contacts to be just made
(closed) when a gauge of the specific dimension is inserted between the armature
residual screw and core face with the relay energized.
• Break - All front or back contacts are just open when a gauge of a specific
dimension is inserted between the armature residual screw and the core face with
the relay de-energized.
• Break-before-make - In a dependent front-heel-back contact, the back contact will
break before the front contact makes as the relay is energized.
• Makes-before-break - In a dependent front-heel-back contact, the front contact will
make before the back contact breaks.
A complete glossary of terms used in this manual is available in Appendix B.
2.2.2. Contact Groups
There are typically six springs per contact group, furnished in various combinations of
contacts. The AC Vane Relay contact groups contain four springs.
Springs are furnished for each group in various combinations of contacts. For example,
a contact group can have two dependent front-back (FB) contacts or three independent
contacts (front or back).
• A dependent FB contact uses three springs, one for the stationary front (F), one for
the stationary back (B), and one for the movable heel.
• An independent contact uses two springs, one for the stationary contact (front or
back), and one for the movable heel.
P1457, Rev. Nov/07 2–3 Alstom Signaling Inc.