The longwall was operating normally when the AFC stopped. When a restart was attempted the feeder cable was blown out of a 3.3kV flameproof restrained plug, causing an electric arc and endangering a maintenance fitter standing nearby.

DME said the plug and cable had received a force and bending movement which led to undue tension on the retaining screws, causing separation of the cable's phase contacts at the thimbles.

This in turn led to heating and arcing in the interior moulding where the contact sockets connected to the cable thimbles, and a short circuit fault occurred as the cable was expelled from the back of the plug.

In a similar incident at a different mine, a 3.3kV cable plug was blown out of the receptacle in which it was restrained.

At the time the longwall was starting up after a short down time. As the crusher motor attempted to start the 3.3kV cable receptacle failed and the cable plug was blown out.

Investigations into the second incident found the plug to receptacle seal was missing and the interior moulding fitted to the receptacle did not meet certification requirements shown on the manufacturer’s drawing for the receptacle.

Current volts recorded at the time of the incident were within levels the equipment was designed to withstand, and there was no excess tension on the plug itself.

DME said the incident occurred because an internal electrical fault in the receptacle was not adequately contained.