Patent ID: 8242719

Claim:
A method for connecting at first and second AC electric motors (M 1 , M 2 , . . . MN) to an AC electricity network (L) in a system which comprises a frequency converter (FC), with which the each of the motors is started, and a pair of contactors (S 11 , S 12 , S 21 , S 22 , SNI, SN 2 ) corresponding to each of the motors which are switchable in order to change a source of supply voltage of the corresponding motor from the frequency converter (FC) to the AC electricity network (L), the method comprising: starting control of the pair of contactors which connect the first motor to the frequency converter (FC), stopping the frequency converter (FC) after starting the control of the pair of contactors connected to the first motor, and before changing the source of supply voltage of the first motor from the frequency converter (FC) to the AC electricity network (L), and only then changing the source of supply voltage of the first motor from the frequency converter (FC) to the AC electricity network (L), wherein the contactors are adapted to allow only one of the first and second electric motors to be connected to the frequency converter (FC) at any one time, the other of the first and second electric motors being connected to the AC electricity network (L).