No fewer than three nor more than 30 days before each election, the electoral board or general registrar shall instruct, or cause to be instructed, on the use of the equipment and his duties in connection therewith, each officer of election appointed to serve in the election who has not previously been so instructed. The board or the general registrar shall not permit any person to serve as an officer who is not fully trained to conduct an election properly with the equipment. This section shall not be construed to prevent the appointment of a person as an officer of election to fill a vacancy in an emergency.