An apparatus for electrically insulating a lateral connecting portion of a laminated multi-phase busbar comprises an elongated housing having first second housing sections made of an electrically insulating material that are pivotally connected to each other along a hinge section extending in a longitudinal direction of said housing and an opening arranged opposite to said longitudinal hinge section for receiving a connecting portion of a laminated multi-phase busbar. The first housing section comprises a plurality of first engagement structures and said second housing section comprises a plurality of second complementary engagement structures adapted to engage with said first engagement means when pivoting said first and second housing section towards each other from a first assembling position to a second clamping position.