A 4-pole RCD is used in industrial installations with a three-phase current voltage of 400 V, to protect people from current damage when touching, and for fire safety. Differential relay, additionally equipped with an automatic protection automatic, is used to protect against supervisor. The number of RCDs required to protect in premises is determined by the number of individual lines in the network. For domestic rooms with high humidity, devices are used that work on the leakage current with a force of 10 mA, if there is a threat of people under voltage, then it is recommended to use a differential relay for a current of 30 mA. It is better to choose fire -fighting RCDs with a characteristic of a nominal differential current from 100 mA. Differential relay, depending on the type, can respond to a leakage of constant, or alternating current.
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