scope:

Purpose

Short circuiting bars are provided for use as a last resort to isolate the current to the DC third rail system, also the DC fourth rail systems between Richmond and Gunnersbury or Wimbledon and East Putney, in the following circumstances:

When it is apparent that a person is in danger though contact with the conductor rail.

For the protection of passengers alighting from a train stopped by failure or accident.

When a short circuit on a train cannot be isolated immediately and there is severe arcing.

As specified in the Drivers Manual.