Blue Square Electrical Control System
Battery Isolating Switch
One was provided per power car located on the underframe, normally at the centre of a larger panel that also contained rows of fuses.
Description
From the BUT 50000 Series Service Manual:
This two-pole switch when open, isolates the battery from the remainder of the electrical equipment on the car.
Note — This is NOT a circuit-breaker, therefore all other switches on the car should be opened before this is operated.
Schematic
This shows the connections to the switch, taken from the BUT 50000 Series Service Manual.
When the switch is closed, the battery is connected to circuits 51 and 52, the "Local +" and "Local –" circuits.
A few items are connected direct — the starter motors and "Fire Alarm Control Panels" — but the remaining items are connected after passing through fuses.