Fault currents
There has been recent concern over the failure of electricians to consider fault currents when working on, or near live parts and to design protection systems correctly.
The high levels of energy dissipated during faults can cause damage to plant and property or injury to people.
Some of the issues identified by the Electrical Safety Office include:
- failure to consider fault current when working near live parts
- instruments not suitably rated for prospective fault currents, e.g. Category III or IV
- using alternative fault current protection devices in place of the equipment specified by the designer/ manufacturer
- installation of incorrectly rated protection devices, inappropriate for the fault levels available
- incorrect substitution of cascading protection equipment
- cables incorrectly sized in accordance with AS/NZS 3000:2000 Electrical installations clause 2.4.4.3 e.g. failure to ensure cable temperature rise is within tolerance under fault conditions
- continuing to close circuit breakers onto faults
- failure to adjust moulded case circuit breakers from preset values
- failing to consider the increase in fault current levels caused by transformer upgrades or alternative supplies i.e. generators.
When working on or near live parts, fault current must be considered in a safe system of work. The Code of Practice – Electrical Work, Code of Practice – Working near Live Parts and AS/NZS 4836:2001 Safe working on low-voltage electrical installations (non-Queensland government site) provide guidance on safe systems of work.