The inspectorate said in a safety bulletin that the area of a motor control centre in the vicinity of the incoming cables and circuit breaker presents an area of high risk to electrical persons working in the enclosure.
Often the hazards of live equipment, such as voltmeters and busbars, exist when the main incoming circuit breaker is open.
In a recent incident an electrician came into contact with an exposed 240-volt to earth cable termination on the back of a voltmeter. The terminals were not shrouded. The voltmeter was protected by fuses which were located at the rear of the incoming circuit breaker enclosure.
“This area of a motor control centre, ie from the low voltage cable terminations of the transformer to the line side terminations on the incoming circuit breaker, is a high arc flash energy area,” the inspectorate’s safety alert issued Tuesday stated.
“There is often no electrical protection between the low voltage terminations of the transformer to the line side terminations on the incoming circuit breaker. The level of arc flash energy at the incoming circuit breaker will be high.
“The electrical protection for the load side of the transformer is back at the high voltage circuit breaker or switch fuse unit, which can be up to several hundred metres away and often supplied by underground cable."
Queensland Department of Mines and Energy incident data shows 65 electric shocks to persons have occurred involving inadvertent contact with exposed conductors; 28 have been electrical personnel working on and around switchboards.
Thirty lost-time injury incidents due to burns occurred while people were working on and around switchboards and of 32 fatalities due to electrical energy since 1908, nine have involved electrical personnel working on or around switchboards.
The inspectorate issued the following controls to prevent similar incidents in the future:
- Inspect and test to ensure that all components in the incoming circuit breaker cubicle are well shrouded, with insulation material, against direct contact;
- Mark all shroud covers to indicate status and voltage with cubicle door open;
- Increase the level of protection in the event of short circuit faults. This may include fitting the HRC fault current limiting fuses to the transformer low voltage cable terminations prior to the feeders to the motor control centre; and or fitting the earth leakage detection to the load side of the transformer which trips back to the line side supply high voltage circuit breaker;
- Ensure arc flash energy levels are calculated and appropriate measures put in place to limit the extent of flash burns. This may include reviews of protection trip times and the provision of special clothing when working in the vicinity; and
- Prior to working in the incoming enclosure ensure all energy sources are identified and where necessary are isolated – for example, transformer, bus tie circuit breaker, interpanel control and voltage transformers and auxiliary/stand-by generators.