Originally Posted by
Rick Christopherson
The reason this occurs when he hears the centrifugal switch re-engage, is because the start winding in the motor has stored magnetic energy, and the switch closes to permit this to suddenly drain back into the system. It is an unexpected current that did not originate from the mains.
To clarify Rick's comment just a bit, it's unlikely that the starting winding has any stored magnetic energy. A coil cannot store energy for any appreciable length of time. As soon as current stops flowing in the coil, the magnetic field collapses and can self induce continued current flow. But that happens very quickly and the starting coil has been disconnected from the circuit for a very long time by the time the motor is turned off.
However, in the starting circuit is a capacitor, which can store energy for a very long time. If that discharges (somehow) when the centrifugal switch closes, it can send current someplace.
But that someplace is a problem. For current to flow, you must have a complete circuit. So if you have a capacitor and you touch one pole of the capacitor, you will not be shocked because the current must flow from that pole, through you, to the other pole.
Since the black line has been broken by the time the centrifugal switch cuts in, the only way current could flow in the white line is if there's an arc across the black line switch points, or if the current flows between the white (neutral) and ground.
We're always warned about handing a starting capacitor if disconnecting it shortly after running the motor because it could still have a charge. That's because when the motor is turned off (one line or two) the capacitor may not be able to discharge.
Mike
Go into the world and do well. But more importantly, go into the world and do good.