A valuable article from WaterWorld on the use of GFCI devices in industrial settings
A major water utility that provides drinking water to 3 million residents faced a challenge when performing annual cleaning on their two Olympic swimming pool sized tanks. Each tank contains a 7 to 10 horsepower submersible pump that runs on 600 VAC.
The tanks must be cleaned by hand, requiring workers to enter them with water still present and the pumps running. Due to the conduction of electricity through water, the risk of electric shock increases when water comes in contact with electrical equipment and workers.
In an effort to be proactive regarding safety, the supervisor at this municipal water facility wanted to protect the workers from electrical shock hazards. He asked his electrical distributor for a solution and a ground fault relay was his initial recommendation. However, he later learned of a new device for worker shock protection – an industrial ground fault circuit interrupter (GFCI).
Recent advances have been made in GFCI technology allowing them to provide sensitive, low-level protection without nuisance tripping at higher voltages. In 2012, UL (Underwriters Laboratory) approved the first GFCI for applications up to 600 V. UL 943C defines the characteristics expected of “special purpose” GFCIs operating up to 600 V and separates industrial GFCIs into Classes C, D and E.
- Class C is for use in circuits with no conductor over 300 V to ground where reliable equipment grounding or double insulation is provided.
- Class D is for use in circuits with one or more conductors over 300 V to ground and with over-sized grounding to prevent the voltage across the body during a fault from exceeding 150 volts.
- Class E covers equipment similar to Class D but with high-speed tripping required, not requiring the over-sized ground of Class D.
Industrial GFCIs are especially valuable in situations combining electricity, people and the presence of water; including submersible pumps, aerators, mixers, and equipment subject to wash-down cleaning. Consideration should also be given to damp or wet-work areas or locations where temporary loads are plugged into welding receptacles. Other areas to consider using a GFCI include dewatering pumps used for construction and maintenance activities. Public areas like pools or fountains are also areas with high-voltage pumps where people/water/electricity are frequently combined.