What causes arcing

Learning from accidents: electric arc caused by a short circuit - employees narrowly escaped a serious accident

A company electrician was given the task of removing a badly damaged flexible cable. It was a three-phase device connection cable. This was firmly connected to a distributor (socket combination). The line was retrofitted to the combination.

Various safety elements were built into the distributor. When the flexible cable was subsequently connected, it was neglected to add the labeling of the circuits in the distributor. The company electrician assumed that the flexible cable was connected via the fuse element for the three-phase 16 A socket. Therefore, he switched off the three outer conductors on this fuse element.

Now, to be on the safe side, he wanted to use the two-pole voltage tester to determine the absence of voltage at the damaged area - that is, on the exposed wires of the flexible cable.

When trying to test the individual wires, two of the damaged outer conductors touched each other and triggered an arc. The industrial electrician got away with a great shock. The intensity of the arc was low because the RCD built into the distributor quickly switched off the circuit.

The operational accident investigation showed that two phases of the flexible lines were connected via a fuse element each and one phase via the phase of a three-phase fuse element. After switching off the three-phase fuse element, there were still two phases in the flexible line under voltage.

Accident prevention measures

In principle, compliance with the five safety rules is essential.

  1. Unlock
  2. Secure against being switched on again
  3. Ensure that all poles are free of voltage
  4. Earth and short-circuit
  5. Cover or cordon off neighboring, live parts

Apart from the fact that working under voltage is fundamentally prohibited, the correct switch-off sources (fuse elements) should have been identified in the case described: By opening the distributor, the connection points of the flexible line in the distributor would have to be determined in order to then switch on the correct fuse elements can. It would have been correct to first determine the absence of voltage at the switch-off points and then at the exposed wires for the flexible cable. Only then would it have been possible to start dismantling the defective line, taking into account the principles for working near live parts.