Trailing and reeling cables

Regulation 5.21 requires that trailing and reeling cables must conform to Australian Standard AS 2802 and incorporate a pilot core arranged to cut off the supply of
electricity in the event of a break in the earthing circuit.
Note: There are currently no underground coal mines in Western Australia so AS 1802 does not apply.
Once an earth continuity relay and associated connections of the protection system are installed, the pilot core allows pilot earth loop or earth continuity monitoring
protection to function.
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Why is a pilot core included?
The inclusion of a pilot core allows pilot earth loop or earth continuity monitoring protection to function. It is important to realise, though, that this protection method is
not the same as pilot wire differential protection (where the current entering and leaving a cable is measured and compared).
Rather, earth continuity protection functions by establishing a loop current through the pilot core, returning through the cable earth. This is typically achieved using an
earth continuity protection relay to apply a low voltage DC signal between the pilot and earth of the cable. By measuring this signal, the resistance of the circuit can be
determined and protection operation initiated for variance from a pre-tested value. This variance is indicative of a break in the earth return path of the cable, and
possibly the cable itself. With this arrangement, an end-of-line resistor is required to avoid a short circuit between the pilot cable and the earth.
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Functions required for the earth continuity protection system
For the overall earth continuity protection arrangement, the system must perform the functions listed below.
• The protection system must monitor the status of the earth continuity for any break in the earth return path. Typically, this will require a status indication of earth
continuity healthy, open-circuit or short-circuit.
• In the event that the status of the pilot earth continuity circuit is open-circuit or short-circuit, an interlock must immediately initiate automatic de-energisation of the
mobile apparatus.
• When a fault does occur, the system should require manual reset — the system should latch and thereby store the fault condition in order to prompt fault-finding
and testing.
• The protection system should ideally interface with the control system of the mobile apparatus such that a healthy status indication for the pilot cable is required
prior to start.
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Commissioning and testing required at installation
Earth continuity protection must be installed, commissioned and tested in accordance with the manufacturer’s instructions and recommendations. Regulation 5.21 also