When electricity is passed through the bi-metal strip (This electricity is supplied from the motor supply), it warps from the resistance (or heat), and pushes on the cam to release the cover. It needs at least 5.5 Amps to function properly, about 6 amps of power is passed through the strip.
So to answer your question, because the lead comes off of the motor draw, its somewhere around 120 volts and 6 amps is required to make it warp and open.