The cable tester CTP 3 A facilitates finding the right cable! Just plug the tester to one end of the cable (e.g. in the apartment) and hold the beeper to the other end (e.g. in the cellar). If there is a beep, you found the right cable.
The cable tester also shows short circuits with a red LED at the top of the device. Shipment: cable tester with beeper, adaptor and micro- / AAA battery.