In article ,
Brian Lawson wrote:

On Tue, 18 Sep 2007 06:47:23 GMT, "Leo Lichtman"
wrote:

When I was in school, we synchronized a generator with the utility power by
connecting a light bulb between them. When the bulb went out, they were in
phase, and we threw the switch.
SNIP

Hey Leo,

Old "Preston Chronicle" newspaper report:

--------The cause of death was trauma caused by exploding machinery
when the new plant operator threw the switch to connect the building
generator to the incoming supply. In his previous place of
employment, they had used a "lamp out" system, while this plant used a
"bright light" system to detect phase synchronization.------

And the same is possible if the "lamp" burns out at just the wrong
time, as it is prone to do with the voltage fluctuations during
run-up. Bright-light is not as sensitive, but somewhat safer.

Use two lamps, one "lamp on" (in a green globe), the other "lamp out"
(and in a red globe)?

Joe Gwinn