Alert no. 446 | 21 February 2024 | Version 1

Electric shock from accessing a high voltage enclosure

What happened?

On Thursday 15 February 2024, an electrical worker at an underground coal mine in the Bowen Basin gained access to an 11kv electrical enclosure (refer Figure 1) on a transportable substation. After accessing this enclosure an arcing event occurred and the worker received burns to their left arm and right hand. The worker was admitted to hospital for further treatment.

How did it happen?

A group of electrical workers were tasked with performing maintenance work on the 1000v equipment of an 11kv/1000v underground transformer. During this work an electrical worker opened and entered an 11kv enclosure without following site procedures for access to high voltage conductors.

Key issues

Initial investigations show that:

• high voltage isolation and access procedures may not have been followed.
• testing prior to accessing electrical enclosures may not have been adhered to.

Recommendations

All site senior executives should:

• review preventative access measures for high voltage enclosures, taking into consideration, but not limited to the following (Locks / Cable continuity circuits / Upstream interlocking / Special fasteners and tools / Live line indication / Audible alarms / Visual alarms).
• review their site procedures and interlocking standards against the requirements of Australian Standard AS/NZS 4871.1:2012 section 2.2.6 Interlocking.
• consider Isolation matrixes to clarify isolation processes.
• review differentiation of signage for high voltage and low voltage equipment.

All supervisors should:

• ensure they know and understand the requirements of standard work instructions.
• ensure that the standard work instructions and procedures are available to Coal Mine Workers (CMWs).
• provide leadership and guidance to CMWs, under their control.

All electrical workers should:

• ensure they and their workgroup understand and comply with the standard work instructions/procedures.
• ensure they and their workgroup identify all access isolation requirements.
• conduct hazard identification and risk management before starting a task.
• if unsure of isolation requirements for access to electrical conductors, stop work until confirmation of requirements is determined.

References and further information

• AS/NZS 4871 Electrical equipment for mines and quarries.
• AS/NZS 3007 Electrical equipment in mines and quarries.
• Recognised Standard 01 - Underground electrical equipment and electrical installations