The Schneider Electric G12T4A40 is a fixed-mount GoPact MCCB 125 molded-case circuit breaker, 4-pole (4D protected), rated 40 A at 40 °C with a TM-D thermal-magnetic trip unit providing LI protection — thermal for overload, magnetic for short-circuit. It carries a 10 kA breaking capacity at 415 V AC 50/60 Hz per EN/IEC 60947-2, making it a straight distribution breaker for panel feeder or sub-feed duty. Rated operational voltage is 415 V AC; insulation voltage is 440 V AC.
If your panel runs hotter, you derate — the TM-D thermal element responds to ambient temperature. Electrical endurance is 8000 cycles at rated current and voltage; mechanical endurance is 30,000 cycles. For a distribution breaker switched infrequently (once a month or less), that's ample. If it's used as a manual disconnect cycled daily, watch the electrical count. Power dissipation per pole is 18.7 W, so four poles at full load shed about 75 W into the enclosure. Factor that into your panel thermal budget — especially in a sealed, non-ventilated box.
Mounts fixed to a backplate — not DIN rail. The 100 mm width, 130 mm height, 60 mm depth footprint fits standard panel cutouts for 4-pole MCCBs in the 125 A frame class. Connection pitch is 25 mm; both line and load connections are front-access screw terminals, so you can busbar or cable it without reaching behind the panel. Neutral is on the left, protected at 1 x Ir (full rating). Toggle control with a grey RAL 7035 housing; IP20 finger-safe terminals when wired.