Over half of all electric arcs occur at 277 volts. There are a few reasons for this. One reason is 277 vac is a single phase circuit of a three phase 480 vac circuit. This circuit typically provides considerable fault current, in amps. A second reason is due to the fact that commercial and industrial lighting circuits are powered by 277 vac due to the fact that 480 vac are readily available. When qualified workers take such circuits for granted, mistakes and errors frequently occur.

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