Arc Flash Hazard Mitigation at Winstone Aggregates Quarry

Winstone Aggregates Quarry operates motor control centres (MCCs) and switchboards that, like many industrial environments, present significant arc flash hazards. These hazards can lead to devastating outcomes such as explosions, severe burns, equipment damage, and extended operational downtime.

Under AS/NZS 4836:2011 and Electrical Safety Regulation 100, arc flash is recognised as a serious risk within the framework of New Zealand’s Health and Safety at Work Act (HSWA). Fault currents during an arc flash event can surge up to 20 times the rated current, generating incident energy levels that may exceed the protective capabilities of standard personal protective equipment (PPE).

In one documented case, the incident energy was calculated to exceed 40 cal/cm², a level at which no PPE can provide adequate protection. The potential consequences of such an event at Winstone Aggregates include:

• Fatal or life-altering injuries
• Complete destruction of MCC infrastructure
• Legal penalties and financial reparations
• Prolonged plant downtime with multimillion-dollar losses
• Damage to market position and corporate reputation

A WorkSafe-directed audit prompted an arc flash study at the quarry’s MCC. Personnel were routinely required to open panel doors to access insulated bus assemblies for isolating or resetting motor overloads and breakers—activities that exposed them to high-risk conditions.