63 A MCCB with 121 kA interrupting rating — what the numbers mean for your panel
The Siemens 3VA1063-4ED42-0JH0 is a SENTRON molded case circuit breaker (MCCB) rated for 63 A continuous at 40 °C, carrying that full rating up to 50 °C before it starts to derate — 62 A at 55 °C, 61 A at 60 °C, 60 A at 65 °C, 58 A at 70 °C. That thermal curve means you can load it to nameplate in most ventilated enclosures without bumping into the derate. The interrupting ratings tell you where this breaker can go: 121 kA at 240 VAC, 75.6 kA at 415 VAC, 52.5 kA at 440 VAC, and 11.9 kA at both 500 V and 690 VAC. That 121 kA figure at 240 V is the headline — it handles high-fault utility feeds common in North American distribution panels. At 415 V the 75.6 kA still covers most industrial transformer secondaries. Four poles, rated insulation voltage 800 V, line protection design — this is a straight feeder or branch breaker, not a motor-protective device. The 17.3 W max power loss matters for thermal coordination in a sealed enclosure; account for it in your heat budget.