On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
wrote:

In the 'old' days; mains powered clocks (squirrel cage, synchronous) were
common.

This is Usenet isn't it? There'll be complaints....

Of course not all clock motors are shaded pole. The Warren Model A was,
back in 1916 (I think the first synchronous clock motor)

However the well-known Westclox / Sangamo design of the '30s and onwards
used an induction rotor - effectively a "squirrel cage". This gave good
starting torque, but obviously had the slip problem. To keep it locked
and synchronous there was also a permanent magnet rotor. This gave
adequate torque at synchronous speed, without slip, but wouldn't have
been able to start the clock unaided.

Some British designs used a single permanent magnet rotor and required a
mechanical pushbutton, or an extra winding for starting.