AC type RCDs are only sensitive to sinusoidal type fault currents. A type RCDs, on the other hand, are sensitive to both sinusoidal currents and “unidirectional pulsed” currents, which may be present, for example, in systems with electronic devices for rectifying the current. These
devices are capable of generating pulsed‐shape fault currents with continuous components that an AC type RCD is unable to recognize. B type RCDs, besides being able to protect against sinusoidal and “unidirectional pulsed” fault currents, also protect against DC earth fault currents above 6mA DC. They also protect against high frequency fault currents.
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