The Siemens SENTRON 3VA2125-8HN42-0AA0 is a 4-pole molded case circuit breaker (MCCB) rated for 25 A continuous current across the full ambient range from 40 °C to 70 °C — no derating needed up to that ceiling. It carries a 300 A frame, meaning the interrupting mechanism and bus are sized for that maximum, while the trip unit is set for 25 A. Breaking capacity hits 440 kA at 240 V, 330 kA at 415 V, 220 kA at 500 V, and 52.5 kA at 690 V, so it handles high-fault utility feeds and transformer secondaries without cascading upstream.
The 86 mm depth (3.39 in) is the dimension from the mounting surface to the front of the breaker — check gland-plate clearance if the panel door closes tight.
For a 25 A feeder on a 1000 kVA transformer secondary (prospective fault current typically 25–50 kA), this breaker has substantial headroom. The ETU350 release allows field-adjustable long-time pickup and short-time delay, so you can coordinate with downstream breakers without changing the trip unit.