Line-down spare: what fits, what doesn't
The Siemens 3VA1163-3EF32-0AG0 is a SENTRON molded case circuit breaker (MCCB) spec'd for line protection — 3-pole, 63 A continuous at 40 °C, with a TM240 thermal-magnetic release. That TM240 means the thermal pickup is fixed at 63 A; the magnetic trip is adjustable between 5–10× In (315–630 A). It's current-production, so no last-time-buy scramble. Breaking capacity is the headline: 75.6 kA at 240 V, 52.5 kA at 415 V, 32 kA at 440 V, and it still holds 11.9 kA all the way up to 690 V.
Thermal derating: the real-world current
At 55 °C it drops to 62 A, at 60 °C to 61 A, at 65 °C to 60 A, and at 70 °C to 58 A. That's a shallow slope; if your panel ambient is 65 °C you still get 60 A, which is 95% of nameplate. The maximum power loss is 17.3 W, so enclosure heat rise is manageable with standard ventilation.
The width is important for multi-breaker groupings: 76.2 mm per pole center matches the standard 25.4 mm pitch, so three poles occupy three module spaces on a DIN-rail adapter plate. If this lives in an unheated enclosure in a northern climate, the cold-start behavior is fine — the thermal-magnetic release isn't affected by low ambients the way electronic trips can be.