An apparatus (100, 400) comprising: - a tool (102, 402) comprising a first portion (106, 406) and a second portion (108, 408) at least partially surrounding the first portion, wherein the first portion is configured to receive a conductor (202, 411, 504) and the second portion is configured to hold a measurement coil (110, 404, 502); and - a holder (104, 300) configured to be detachably attached to the tool (102, 402), wherein the holder is to be employed to install the tool holding the measurement coil (110, 404, 502) onto a conductor (202, 411, 504), wherein the first portion (106, 406) is configured to snap fit onto the conductor (202, 411, 504) during installation, and the measurement coil (101, 404, 502) at least partially surrounds the conductor when installed, characterised in that the first portion (106, 406) and the second portion (108, 408) form a one-piece structure of flexible material; the first portion (106, 406) is formed of an open-curved wall and a plurality of interconnected elements (114, 116) configured to extend inwards from the open-curved wall towards a centre portion of the tool (102, 402) to apply a force onto the conductor (202, 411, 504), when installed, and accommodate the conductor in the centre portion thereof, and the second portion (108, 408) is formed of a plurality of fingers (120, 122) spaced apart, extending outwardly from the first portion (106, 406), each finger having an inner wall connected to the first portion (106, 406), an outer wall in parallel with the inner wall and a laterally extending base, defining a recess therebetween, and an aperture opposite the base to allow snap-fitting of the measurement coil (110, 404, 502) into said recess to hold the measurement coil when installed - a tool (102, 402) comprising a first portion (106, 406) and a second portion (108, 408) at least partially surrounding the first portion, wherein the first portion is configured to receive a conductor (202, 411, 504) and the second portion is configured to hold a measurement coil (110, 404, 502); and - a holder (104, 300) configured to be detachably attached to the tool (102, 402), wherein the holder is to be employed to install the tool holding the measurement coil (110, 404, 502) onto a conductor (202, 411, 504), wherein the first portion (106, 406) is configured to snap fit onto the conductor (202, 411, 504) during installation, and the measurement coil (101, 404, 502) at least partially surrounds the conductor when installed, characterised in that the first portion (106, 406) and the second portion (108, 408) form a one-piece structure of flexible material; the first portion (106, 406) is formed of an open-curved wall and a plurality of interconnected elements (114, 116) configured to extend inwards from the open-curved wall towards a centre portion of the tool (102, 402) to apply a force onto the conductor (202, 411, 504), when installed, and accommodate the conductor in the centre portion thereof, and the second portion (108, 408) is formed of a plurality of fingers (120, 122) spaced apart, extending outwardly from the first portion (106, 406), each finger having an inner wall connected to the first portion (106, 406), an outer wall in parallel with the inner wall and a laterally extending base, defining a recess therebetween, and an aperture opposite the base to allow snap-fitting of the measurement coil (110, 404, 502) into said recess to hold the measurement coil when installed