Robbie comments about frequency tolerances for transformer type line
conditioners:

> The ordinary transformer doesn't offer the protection that the resonant
> line conditioner provides.  The two types are often installed together,
> however.  The line conditioner is usually rated for +/- 5% change in
> mains frequency, or +/- 3 Hz at 60 Hz.  -- Robbie >>

If I remember correctly, one of the original thread questions related
a local grid be disconnected from the mains and then motors, etc.
dumping high voltage into said local grid.  This is not my area, but,
I doubt we would see anything like a stable 60 Hz frequency under these
circumstances.

Will Dahlgren

 [ That's true, and the line conditioner is designed to deal with this
 [ condition also.  The ANSI/IEEE C62.41 specification has a gruesome test
 [ for 120-volt equipment: 390 vdc is suddenly added to the ac at the
 [ crest of the sine wave (170 v), making it 560 volts!  The dc voltage
 [ then decays exponentially over one cycle (16 msec).  One of the two
 [ transformers in the line conditioner unit simply saturates during this
 [ event, safely absorbing the surge.  The other transformer is the
 [ inductor of 60-Hz resonant "flywheel" circuit, and it provides
 [ additional suppresion of the transient pulse.  -- Robbie