A Latent Electrical Hazard – An arc flash incident

A team of electricians was removing redundant electrical cables from a 440 volt switchboard at a Pilbara Iron Ore Mine.

The task was to remove “Dead – Non-Energised” redundant electrical cables from the switchboard by externally pulling the cable out of the switchboard via the cable gland outlets.

No contact or entry was required into the switchboard during this work and the switchboard busbars remained live during the cable pulling.

The switchboard door was opened to enable the apprentice electrician to observe and report on the cable removal and any obvious issues.

Whilst the cable was being pulled out there was a loud bang and an arc flash in inside the cabinet.

The apprentice suffered burns to his face but his eyes were protected by his safety glasses. His body was also protected as he was wearing cotton clothing. (Non-flammable and did not melt).

A small nut found welded between two bus bars was the cause of the flash-over. It was determined that the nut had been left sitting free in the cabinet – some time previously (probably construction) and had been dislodged when the cable was being pulled out of the cabinet.