What this MCCB is and what it does
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 ETU350 electronic trip unit provides adjustable overload and short-circuit protection curves — line protection design, not motor or generator duty.
Dimensions and panel fit
At 140 mm wide, 181 mm tall, and 86 mm deep, this MCCB fits standard SENTRON 3VA panel cutouts and busbar systems. 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. IP40 on the front face means tools or fingers won't contact live parts, but the breaker is not sealed against water ingress; mount it in a dry enclosure.
What the ratings mean for your application
The 440 kA at 240 V and 330 kA at 415 V are the interrupting capacities — the maximum fault current the breaker can safely clear. For a 25 A feeder on a 1000 kVA transformer secondary (prospective fault current typically 25–50 kA), this breaker has substantial headroom. The 800 V rated insulation voltage (Ui) means it is suitable for 480/277 V and 600 V systems with margin. 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. No undervoltage release, no ground-fault monitoring, no communication function — this is a straight line-protection breaker.