TELECOM Digest OnLine - Sorted: 25 Hz power

25 Hz power

jsw (
Wed, 8 Mar 2006 12:45:38 CST

>> We were still operating units 25 hz 24, 25 and 26 and a reversable
>> frequency changer.

> Who bought this 25Hz power?

IIRC, and somebody please correct me if I'm wrong, 25Hz power was used
even in residential settings up into the early 50's in some parts of
eastern Canada.

In NYC up into the 70's at least, power for two of the subway
divisions (BMT and IRT) was generated at 25Hz but converted to DC in
the field. However, I very distinctly remember the flicker of the
incandescent lamps in some of the BMT stations in the 60's, as these
were operated from the unrectified 25Hz source. I do remember that
some people claimed they could not see this flicker, but it was very
obvious, to me, anyway.

As another trivia point, commercial DC power was still available to
some grandfathered customers in parts of Manhattan until just a few
years ago.

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