This is a Siemens SENTRON 3VA2063-5HL36-0DH0, a 3-pole molded case circuit breaker (MCCB) rated for 63 A continuous current across its full ambient temperature range from 40 °C to 70 °C — no derating needed up to that ceiling. It's a line-protection design, so it's the main overcurrent guard between the transformer or bus and a downstream distribution panel. The interrupting capacity is what earns its place: 187 kA at 240 V, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, and 3 kA at 690 V.
The 63 A rating means it uses a 63 A frame (not a 100 A frame), so it's compact for its interrupting class. If you need remote trip indication, the HQ alarm switch covers that.
