The ABB GSH202 AC‑D25/0.03 is a two‑pole residual current operated circuit breaker (RCCB/RCD) designed for electrical safety in low‑voltage AC distribution systems. It provides protection against earth leakage faults by rapidly disconnecting circuits when an imbalance between live and neutral currents exceeds 30 mA, helping to prevent electric shock and reduce fire risk. The AC‑D characteristic indicates that the device is sensitive to both standard AC residual currents and high‑frequency components typical of certain load types. This compact DIN‑rail mountable unit is suitable for residential, commercial, and light industrial installations requiring enhanced earth‑fault protection.