Help me understand this load detecting circuit
For those not familiar with woodworking, this device is intended to be installed in the power feed to a table saw, and will start a vacuum to collect sawdust when the saw is operating.

If you remove the bridge rectifier, you will see that the 6 volt winding of the transformer is connected in series with one leg of the AC.

As the bridge rectifier is wired it is effectively two pairs of series-connected diodes, with the pairs connected with opposite polarities, like so:







simulate this circuit &ndash; Schematic created using CircuitLab

When the saw is operating, the diodes will produce a voltage drop of about 2 volts which will be stepped up by the transformer to produce sufficinet voltage to operate the relay to start the vacuum.