The Schneider Electric G12T3A63 is a 3-pole GoPact MCCB 125 moulded case circuit breaker with a 63 A TM-D thermal-magnetic trip unit, rated at 40 °C ambient. It's built for distribution duty in panelboards and sub-distribution boards, not motor-starting — the utilisation category is A, meaning it's not intended for frequent switching of loads like contactors handle. It's a fixed-mount, backplate-mounted breaker with front-facing screw terminals for both line and load connections.
The TM-D trip unit gives you LI protection: L for thermal overload (inverse-time, handles sustained overcurrents like a stalled motor or overloaded circuit) and I for magnetic short-circuit protection (instantaneous, clears a hard fault fast). The 63 A rating is the thermal pickup — it'll hold 63 A continuous and trip on a sustained overload above that. The magnetic trip threshold isn't listed here, but TM-D units typically trip instantaneously around 10x In for distribution applications. Electrical durability is 8000 cycles at rated current and voltage — that's fine for a distribution breaker that sees infrequent operation. Mechanical durability is 30,000 cycles, which covers the life of the mechanism. Power dissipation is 18.7 W per pole, so at 63 A load, expect about 56 W total heat to manage inside the enclosure.
Mounts flat on a backplate — no DIN rail clip here. Dimensions are 130 mm high, 75 mm wide, 60 mm deep. The 25 mm pole pitch matches standard busbar systems. Screw terminals front-connect both line and load sides. Mounting position can be horizontal or vertical, which gives flexibility in panel layout.