A terminal box for a centrifugal pump is releasably connectable to an electronic extension module by a locking element. A pluggable electric interface extends through an opening from an underside of the base plate into the terminal box to electrically connect the pump control for establishing a data link. The locking element is slidable in the cavity and is movable manually from a first position to a second position and by a tool from this second position to this first position. It also has on a first side a resilient latch engaging with either a first recess of the terminal box and holding the locking element in the first position, or a second recess of the terminal box holding the locking element in the second position. Thus the locking element frees the module for plugging-in in the first position, and arrests the module in the second position.