What it is and what it does
The Siemens 3VM1332-5MH32-0AA0 is a SENTRON molded case circuit breaker (MCCB) rated for 320 A continuous at 40 °C, with a TM120M thermal-magnetic overcurrent release. Three poles, no trip indicator, no undervoltage release, no ground-fault monitoring — a straight feeder or main breaker for distribution panels. Breaking capacity is 187 kA at 240 V, 121 kA at 415 V and 440 V, and 76 kA at 500 V — numbers that put it squarely in high-fault-duty commercial and industrial switchboards. The 800 V rated insulation voltage means it can sit on a 480 V or 600 V bus without derating the dielectric.
Thermal derating — the real continuous current
The 320 A rating holds flat from 40 °C through 50 °C. Above that it steps down: 313 A at 55 °C, 306 A at 60 °C, 299 A at 65 °C, 292 A at 70 °C. If your panel ambient runs hot — say a non-climate-controlled enclosure near a furnace line — the 70 °C figure is the one to size against.
Panel fit and integration
Dimensions are 248 mm high, 138 mm wide, 110 mm deep — a standard 3-pole MCCB footprint that fits most DIN-rail or panel-mount enclosures. IP40 on the front face means it is protected against solid objects over 1 mm but not sealed against moisture; keep it inside a rated enclosure.