Hazards During Ground Faults on 480-V Grounded Systems

It is known that arcing ground faults on 480-V systems are often too small to actuate phase protective devices. GFI's have been introduced to ensure clearance of such faults. They are costly when used in quantity and are mandatory only on large-capacity circuits. Their use will, therefore, be limited. The hazard of exposure voltages which are not removed by phase protective devices, therefore, remains of great concern. The magnitude of exposure voltage on several common wiring systems is explored and the relative safety evaluated. Different systems produce exposure voltages with maximums ranging from 40 to 190 V. Means are presented for reducing the exposure voltage on those systems that are most hazardous.