Arrangement comprising - a terminal box for a centrifugal pump accommodating a pump control, - an electronic extension module extending the pump control by at least one additional hardware and/or software function, and - at least one locking element for securely holding the module at the terminal box the module being removeably mountable at the terminal box and having a pluggable electric interface (6, 6a) extending from the underside of a base plate through an opening (9, 10) into the terminal box to electrically connect the pump control for establishing a data link, characterized in that the locking element - is slidably accommodated within a cavity of the terminal box and can be moved tool-less from a first position to a second position and removed from said second position to said first position by means of a tool, - having, at a first side, a resilient latch engaging with either a first recess at the terminal box keeping the locking element in the first position, or a second recess at the terminal box keeping the locking element in the second position, - further being configured to give free way for plugging the module in the first position, and to arrest the module in the second position by means of at least one projecting bar (17, 18) arranged at a second side of the locking element, and the module comprising at least one pillar (20, 20a, 20b) extending in parallel to the electric interface (6, 6a) from the base plate and the pillar (20, 20a, 20b) being insertable through an opening into the cavity, when the locking element is in the first position, the pillar (20, 20a, 20b) having a notch for engaging with the bar (17, 18) in a form-fit manner, when the locking element is in the second position. - a terminal box for a centrifugal pump accommodating a pump control, - an electronic extension module extending the pump control by at least one additional hardware and/or software function, and - at least one locking element for securely holding the module at the terminal box the module being removeably mountable at the terminal box and having a pluggable electric interface (6, 6a) extending from the underside of a base plate through an opening (9, 10) into the terminal box to electrically connect the pump control for establishing a data link, characterized in that the locking element - is slidably accommodated within a cavity of the terminal box and can be moved tool-less from a first position to a second position and removed from said second position to said first position by means of a tool, - having, at a first side, a resilient latch engaging with either a first recess at the terminal box keeping the locking element in the first position, or a second recess at the terminal box keeping the locking element in the second position, - further being configured to give free way for plugging the module in the first position, and to arrest the module in the second position by means of at least one projecting bar (17, 18) arranged at a second side of the locking element, and - is slidably accommodated within a cavity of the terminal box and can be moved tool-less from a first position to a second position and removed from said second position to said first position by means of a tool, - having, at a first side, a resilient latch engaging with either a first recess at the terminal box keeping the locking element in the first position, or a second recess at the terminal box keeping the locking element in the second position, - further being configured to give free way for plugging the module in the first position, and to arrest the module in the second position by means of at least one projecting bar (17, 18) arranged at a second side of the locking element, and the module comprising at least one pillar (20, 20a, 20b) extending in parallel to the electric interface (6, 6a) from the base plate and the pillar (20, 20a, 20b) being insertable through an opening into the cavity, when the locking element is in the first position, the pillar (20, 20a, 20b) having a notch for engaging with the bar (17, 18) in a form-fit manner, when the locking element is in the second position.