A Zone Selective Interlocking, ZSI, arrangement in a power distribution system, the ZSI arrangement comprising a first trip unit (610, 700) disposed in a first zone of the power distribution system, a second trip unit (620, 700), and a third trip unit (640, 700), each trip unit being associated with respective circuit breaker within the power distribution system, the first trip unit (610, 700) comprising: an Input/Output circuit comprising a ZSI input terminal and a ZSI output terminal, wherein the ZSI input terminal is configured as an input mode responsive to a fault condition comprising a short-circuit or a ground-fault in the power distribution system, and configured as an output mode responsive to a normal condition without the short-circuit or the ground-fault in the power distribution system, and wherein the ZSI output terminal is configured as an output mode responsive to the fault condition and as an input mode responsive to the normal condition; a heartbeat signaling module configured to transmit a second signal to the second trip unit (620, 700) in a lower-level zone of the power distribution system than the first zone, the second signal being responsive to the normal condition; a first monitoring module configured to monitor a first signal received by the first trip unit (610, 700) from the third trip unit (640, 700) in a higher-level zone of the power distribution system than the first zone, the first signal being responsive to the normal condition, wherein the first trip unit further configured to enable detection of a loose or broken ZSI cable after a wait time period that is longer than a period of the first signal; and a second monitoring module configured to detect the fault condition; characterized in that the second trip unit (620, 700) comprises a self-interlocking jumper, and wherein the self-interlocking jumper is configured to couple a ZSI input terminal of the second trip unit (620, 700) with a ZSI output terminal of the second trip unit (620, 700). an Input/Output circuit comprising a ZSI input terminal and a ZSI output terminal, wherein the ZSI input terminal is configured as an input mode responsive to a fault condition comprising a short-circuit or a ground-fault in the power distribution system, and configured as an output mode responsive to a normal condition without the short-circuit or the ground-fault in the power distribution system, and wherein the ZSI output terminal is configured as an output mode responsive to the fault condition and as an input mode responsive to the normal condition; a heartbeat signaling module configured to transmit a second signal to the second trip unit (620, 700) in a lower-level zone of the power distribution system than the first zone, the second signal being responsive to the normal condition; a first monitoring module configured to monitor a first signal received by the first trip unit (610, 700) from the third trip unit (640, 700) in a higher-level zone of the power distribution system than the first zone, the first signal being responsive to the normal condition, wherein the first trip unit further configured to enable detection of a loose or broken ZSI cable after a wait time period that is longer than a period of the first signal; and a second monitoring module configured to detect the fault condition; characterized in that the second trip unit (620, 700) comprises a self-interlocking jumper, and wherein the self-interlocking jumper is configured to couple a ZSI input terminal of the second trip unit (620, 700) with a ZSI output terminal of the second trip unit (620, 700).