Operator receives shock from overhead crane

Mine type

All mine types

Incident

A crane operator and his assistant received multiple electric shocks from an overhead crane that developed an intermittent electrical earth fault.

Equipment

Overhead gantry crane

Hazard

High resistance in the earth circuit of the crane electric's prevented the earth leakage relay from isolating power when the earth fault occurred. The operator went on using the crane after receiving the initial shocks.

Cause

The high electrical earth resistance through the crane wheel and rail connection prevented the installed 100mA earth leakage circuit breaker fitted to the crane supply circuit breaker from operating. The intermittent electrical earth fault on the overhead crane occurred each time the crane was stopped and tracked through the two operators in turn.

Comments and recommendations

• It is a requirement for all mains supplied cranes to be earthed effectively and comply with AS/NZS 3000 Wiring rules and AS 1418.1 Crane code. Clearly the overhead crane installations that rely on earth connection being maintained between the wheel and rail need regular checking to ensure the earth bond is low in resistance.
• Engineering solutions such as an auxiliary collector earth wire are among those methods that have been employed to ensure this style crane is effectively continually bonded to earth.
• It is not recommended that known or suspected electrical equipment remains in service. All faulty electrical apparatus must be withdrawn from service and be repaired by a competent electrical tradesperson.

Authorised by Peter Minahan - Chief Inspector of Mines

Contact: minesafetyandhealth@dnrm.qld.gov.au

Issued by Queensland Department of Mines and Energy