A knife switch assembly (1) comprising a pair of hinged contact knives (3, 5), arranged parallel to each other and connected to each other at a first respective end (31, 51), and moveable between at least two positions, and a first electric contact element (13) comprising a current carrying conductor (15), said contact knives being made of an electrically conductive material and being electrically connected at said first end (31, 51) to a first electric conductor (9). The assembly further comprising an operator device (11) for moving said pair of contact knives between the at least two positions, of which a first position is an open position in which a respective second end (32, 52) of the contact knives (3, 5) is disconnected from any electrical contact, and a second position is a first contact position in which said respective second end (32, 52) of the contact knives is in electrical contact with the first electric contact element (13). The assembly is characterized in that it comprises a guide member (17; 27) located between the two contact knives (3, 5), said guide member having two projecting side parts (171, 172; 271, 272), each projecting side part extending along at least part of a respective side of each contact knife , which side faces a corresponding side of the other contact knife, and that said guide member (17; 27) is made of a non-conductive material and has a shape adapted to receive the first electric contact element (13) between the two projecting side parts (171, 172; 271, 272). An electric power distribution switchgear is also disclosed and a method for preventing electric discharges.