At a wood products manufacturing plant, a three-phase motor was single-phasing. To find out why, an electrician was testing the incoming voltage to the electrical components inside a 600-volt 600-amp main service panel. A planerman was assisting by holding the multimeter, which was rated at 600 volts and was not CSA-certified. There was a flashover across the circuit board inside the multimeter. The arc ignited sawdust in the service panel. A sudden fireball caused burns to both workers.

• Practise regular housekeeping to keep dust from building up around service panels.
• Keep the covers to all electrical panels closed unless an electrician is working on the panel.
• Have an electrician perform regular maintenance to keep service panels clean inside, especially when they are exposed to contaminants such as sawdust.

• Use a good-quality multimeter with external fused leads when measuring voltage on energized electrical equipment. Fuses and thermal resistors inside older multimeters cannot react quickly enough to protect against sudden spikes in voltage.
• Expect line voltages to be 20 percent higher than rated when build-out capacitors are connected to the electric circuit. The investigation found that build-out capacitors may have caused higher than rated voltages at the motor input terminals.
• Use a multimeter rated at least 25 percent higher than the expected voltage when testing energized electrical equipment. This allows for spikes in voltage.
• Use electrical testing equipment that is CSA-certified or meets other specific safety requirements.