The Siemens SENTRON 3VA4120-5ED14-0AA0 is a 1-pole molded-case circuit breaker (MCCB) with a TM210 thermal-magnetic release, rated 20 A at 40 °C. It's built for system protection in distribution panels — the single-pole form factor (25.4 mm wide) saves rail space on branch circuits where you only need to break the line conductor. The 85 kA interrupting rating at 120 V AC means it can handle high-fault scenarios common in industrial lighting or control transformer feeds without cascading failure upstream. At 277 V it still clears 35 kA, and at 347 V it holds 18 kA — that covers most North American 347/600 V lighting and small power circuits. The IP40 front protection keeps dust and tools out of the breaker face in a closed panel.
The 3VA4120-5ED14-0AA0 snaps onto a standard DIN rail — 25.4 mm wide, 129.4 mm tall, 75.1 mm deep. That single-pole width means it occupies one 1-inch module position.