What it is and what it does
The Siemens 3VA1112-3EE32-0AA0 is a SENTRON molded case circuit breaker (MCCB) built for line protection — the primary disconnect and short-circuit protection in a distribution panel or machine load center. Three poles, rated 125 A continuous at 40 to 50 °C ambient, with a TM220 thermal-magnetic overcurrent release that handles both overloads and short events without external control wiring. Breaking capacity hits 75.6 kA at 240 V, derating to 52.5 kA at 415 V and 11.9 kA at 690 V, so it clears high-fault utility feeds or transformer secondaries where the available current is serious.
Thermal derating and real-world current
Rated 125 A up to 50 °C, then it steps down: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, 114 A at 70 °C. That curve matters if this breaker sits in a crowded enclosure with other heat sources — a 70 °C internal panel temp clips the continuous rating by nearly 9 %. The maximum power loss is 28.1 W, which is the heat the breaker dumps into the cabinet; factor that into your thermal budget if you're stacking several MCCBs on a DIN rail.
Mounting and panel fit
Width is 76.2 mm (3 in) — standard 3-pole MCCB footprint for a 125 A frame. Depth is 70 mm, height 130 mm. No voltage trip or undervoltage release built in, no communication module, no ground-fault monitoring. IP40 on the front keeps dust out of the mechanism; fine for indoor panel mounting. No trip indicator, so you'll need a visual check or a remote auxiliary contact if you want panel-door indication.