We recently investigated several incidents where switchboard wiring had been damaged, resulting in active conductors shorting to either earthed switchboard enclosures or neutral bars inside the switchboard.
When a fault occurs between an active conductor and earth or neutral within a switchboard, the fault current can cause an arc flash which can injure workers and damage property. The switchboard and installation earthing system will be live during the fault, creating the risk of electric shock to the person working on the switchboard and people nearby.
Three common mistakes were identified as contributing factors to these incidents.
- Wiring on hinged meter panels was pushed onto uncovered neutral links installed behind the hinged meter panel when it was closed (as there is often very little room between them in modern switchboards), resulting in cable damage and a short circuit.
- Wiring was not appropriately secured to prevent cables contacting metal edges near the meter panel hinge points. Cables pushed against the metal edges were damaged, resulting in a short circuit to the switchboard enclosure.
- Wiring was not suitably fixed at the hinged panel and the switchboard, resulting in movement at terminals of electrical equipment and energised cables being dislodged from the terminal.
Every switchboard is different, but electrical workers and contractors must ensure that switchboard wiring is electrically safe when installed. This includes fixing cables so they don’t suffer damage, cause pressure on electrical equipment, or stress on terminals when the panel is moved.
An example of good design and work practice is shown below:
For more information, refer to the Wiring Rules:
- section 1.4.39 – contact, indirect
- section 2.10.6 – switchboard wiring
- section 220.127.116.11 – mechanical damage
- section 18.104.22.168 – other mechanical stresses.