In article ,
Frank Erskine writes:

I was once given a beautiful brass timeswitch from a GPO telephone
box. It had been used in East Durham, where the supply was 30 c/s at
about 200 V. I believe the supply came from nearby collieries, which
generated thir own power and fed a few "customers".

It was very common for large industrial concerns to generate
their own electricity. Where large motors where driven, often
lower frequencies were used. 16 2/3rds Hz was a frequency used
by some very large motors.

--
Andrew Gabriel