"Boltar" wrote:

Why do the trains on the NLL switch over to 25Kv AC at Hackney Wick
and then switch back to DC at Dalston when the 3rd rail is continuous
along that section anyway? Why not just stay on DC and save the wear
and tear on the pantograph?

Because the DC supply in that area is somewhat constrained, and only allows
a limited number of simultaneous train movements.*

No time to check, but I believe the NLL timetable is more intensive than
when that section was first used by the 2-EPBs.

Chris

* So says Mr Rob Curling on Video 125's 'North London Line Drivers Eye
View'.