"Sim" wrote

Some differences between Overground and Underground:
1. Third rail electrification rather than fourth, so not compatible
for through running.

The NLL is 25 kV OHLE between Acton and Camden Road, and between Dalston
Kingsland and Stratford, and will be all the way between Acton and Stratford
once the NLL refurbishment is complete. The WLL switches from 25 kV OHLE to
3rd rail between North Pole Junction and Shepherds Bush. Goblin remains
diesel worked (and if it is electrified it will be 25 kV OHLE.

BTW, the Broad Street to Dalston line, most of which is being incorporated
into the ELL, was originally 4th rail, but IIRC was converted to 3rd rail
before closure.

Peter