Organisational Factors » LTA investigation of prior incidents

18Failure To Properly Isolate Electrical Conductors

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

At approximately 1pm on a Friday afternoon an electrician received an electric shock from 240V control wiring while working inside a motor control centre cubicle. Prior to the commencement of work, conductors had been tested for dead using an Easy Scan device. A live phase was detected but voltage present was believed to be as a result of capacitance or electromagnetic coupling from VF drives operating from another motor control centre. The work was completed and the shock reported at end of shift to the shift supervisor who requested that an incident form be completed - this was not done. The following Monday the supervisor reported the shock to the Electrical Engineering Manager. An investigation was started immediately and it was discovered that a phase in the isolator for the motor control centre did not break when the isolator was opened.

Identified Root Causes:

The internal mechanism of the circuit breaker was broken which prevented one phase out of three breaking when the isolator was opened.

All three electricians working at the plant had received at least one shock each at the same location in preceding years. An assumption amongst all electricians existed that the voltage present was not mains supply and was thus harmless - both wrong and potentially fatal assumptions.

Energy Type(s) Involved:

Direct contact with live electrical conductors

Equipment Type(s):

Isolators for electrical equipment

Root & Contributing Cause(s):

LTA isolation

LTA Isolation hardware

LTA maintenance work method

Stated or Potential Consequence(s):

Potential Fatality

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

1. Review procedural controls for access to electrical conductors to ensure the method and equipment to be utilised is adequate.

2. Implement a system of task observation and review of procedural controls to ensure the stated way is being performed.

3. After any incident or after identifying any hazard ensure that the situation is safe for yourself and others to the best of your ability and resources. Ensure no one is put at risk or put at further risk.

4. Ensure that all employees are aware of their obligation to report all hazards, incidents, accidents and injuries.

Don't assume anything always verify and check. The person who is responsible for management of risk is the person with the most ability to control it - This is everyone's responsibility!


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


Here are the results.


Reference Type:

Safety Alert #72

Mine Type:

Any Mine Type







Australia, Queensland

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