B switch units are available in only one size - 5 x10

up to three of them can have their O/L's commoned together to give a B switch of 15 x 10.

Five such 15 x 10 B switches are used in every full major of 3 A switches.

The B switch itself contains only a cross point matrix. It contains no test access relays, control or alarm equipment

Selection Sequence

1. When the A pattern Relay's operate, theT & M wires of the A-B trunks ( B switch Inputs) are extended to the B switch Selector

2. When the B switch selector make sits choice it extends a +7.5v mark on the chosen M wire

3. When the C switch crosspoint relay operates the 15v form the C switch is extended on a H wire to the B switch and the cross point relay operates.

4. When the common equipment releases the A pattern relays release and the Mark in released from the M Wire

Release

On a normal cleardown release of the supervisory relay set releases the Crosspoint.