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103Switchboard Incoming Supply Hazards

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Brief Description of Incident/Accident & Description of Consequences/Outcomes:

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, e.g. voltmeters and busbars, exist when the main incoming circuit breaker is open.

Recently an electrical tradesperson came into contact with an exposed 240 volt to earth cable termination on the back of a voltmeter. The terminals were not shrouded, as shown in figure 1. The voltmeter was protected by fuses which were located at the rear of the incoming circuit breaker enclosure.

Energy Type(s) Involved:

Electrocution due to contact with exposed live parts at 240 volts and above.Arc fault energy developed as a result of a short circuit fault.

Equipment Type(s):

Motor Control Centre

Root & Contributing Cause(s):

LTA awareness

LTA equipment

LTA hazard identification

LTA isolation

LTA work method

Stated or Potential Consequence(s):

Potential Fatality

Preventative/Recommended/Accepted Steps of Risk Mitigation, Points of Interest:

The controls necessary to prevent similar incidents may include one or more of the following:

  • 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 one or more of the following:

o Fit HRC fault current limiting fuses to the transformer low voltage cable terminations prior to the feeders to the motor control centre.

o Fit 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.
  • Prior to working in the incoming enclosure ensure all energy sources are identified and where necessary are isolated, e.g. transformer, bus tie circuit breaker, interpanel control and voltage transformers and auxiliary/stand-by generators.


Queensland Government Department of Employment, Economic Development and Innovation (DEEDI)


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Reference Type:

Safety Bulletin #73

Mine Type:

Any Mine Type







Australia, Queensland

ICAM Categories

Organisational Factors

• LTA commissioning procedures

• LTA equipment integrity

Task or Environmental Conditions


Individual or Team Actions

• LTA hazard identification

Failed or Absent Defences


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