An earth leakage relay monitors residual current and trips a companion circuit breaker or contactor when leakage exceeds a set threshold. The 5TT30010Y is the relay module itself — not the toroid, not the breaker. You pair it with a separate core-balance transformer and a shunt-trip or undervoltage-release accessory on the upstream breaker. Typical install is in a distribution panel feeding industrial or commercial loads where ground-fault protection is required by code or by process (e.g., wet environments, livestock buildings, temporary power).
Physical handling note
At 4.54 kg, this is a substantial relay module — not a DIN-rail component you toss in a bag. Plan for a separate shipping carton and a handling step during panel assembly. The weight suggests a robust enclosure with internal components rated for industrial vibration and thermal cycling.