Network Rail KSW Sectional Appendix - SO250 Pantograph on the move
Class 378 drivers are authorised to change over traction modes using the following,

Maintain 25mph (in 60mph zone) leaving Shepherd's Bush.
Reaching dual voltage zone warning board,
- reduce throttle to 0
- contact shoes up and then pantograph up.

Wait till power change complete message and continue driving.

If signal VC813 is at danger. Stop at AC only zone board
and complete power change.

Note. It might take up to 15 seconds for power change.