“The cables have been poorly located in ‘fixed cable’ racks on the goaf side of the AFC spill-plates at the mid-face area of the longwall, and have been damaged by chock pontoons,” regional inspector of mines Michael Downs said.
Two incidents involved open arcing, whilst in the third conductors were exposed.
In each case, electrical protection circuits isolated the power and limited the extent of electrical arcing.
These cables supply electrical power at 3300 volts to the shearer and the tailgate motors, and are meant to run along the back of the pan line in purpose-designed cable ways.
“The accumulation of excess cable at mid-face is an unacceptable safety risk, as an electrical arc here has the potential to cause the ignition of gas and/or coal dust,” Downs said.
“But while mid-face is the most common point for the migration of cables and looping, it can occur at any point along the cable trays on the pan line with the same high potential for damage.”
The inspectorate made the following recommendations:
- Electrical cables (and hoses) must be anchored and retained on the fixed cable goafside cable trays along the spill-plates. Additional anchors may be required to equalise the strain on the cables throughout the pan line, and if uni-directional cutting is employed on the face more anchor points are likely needed.
- If excess cable develops at mid-face or along the pan line such that the cable protrudes from the cable way, the longwall should be stopped and the loop pulled to the maingate or tailgate as required. The practice of tying up loops of surplus cable may lead to unacceptable levels of risk.
