A switch assembly includes first and second contact members which are operatively provided to take one of two positions, a break-position in which the first and second contact members are separated from each other, and a make-position in which the first and second contact members are electrically connected with each other. Magnetic members are provided operatively in association with the first and second contact members to define a closed magnetic loop with a current path extending through the loop, when the first and second contact members are turned to the make-position. The magnetic members attract each other by the magnetic flux through the closed loop to maintain the first and second contacts in the make-position when the current flowing through the current path is not zero. Thus, the first and second contact members are permitted to return to the break-position at a zero crossing point of a.c. current flowing through the contacts.