What it is and what it does
The Siemens 3VA1140-4GF42-0AA0 is a SENTRON molded case circuit breaker (MCCB) rated for line protection — 40 A continuous at 40 °C, 4-pole, with a TM240 thermal-magnetic trip unit. The 121 kA interrupting capacity at 240 V AC means it can clear a bolted fault at that voltage without the arc re-striking or the case rupturing; at 415 V it still holds 75.6 kA, and at 690 V it's rated 11.9 kA. That's enough SCCR headroom for most 480 V distribution panels downstream of a transformer. Rated insulation voltage is 800 V, so the internal clearances and creepage are designed for 690 V AC systems with margin. The TM240 release is a fixed thermal-magnetic — no electronic adjustment, no communication module, no undervoltage release. It's a straightforward line-protection breaker: trip curve is what it is, no fiddling.
Thermal derating — the real-world current
The 40 A rating holds from 40 °C through 50 °C. At 55 °C it's 39 A, at 65 °C it's 38 A, and at 70 °C it's 37 A. If your panel ambient runs hot — say a packed enclosure near a furnace line — that 3 A drop matters for coordination studies. The maximum operating temperature is 70 °C; storage range is -40 °C to 80 °C.
Mounting and integration
The 3VA1140-4GF42-0AA0 measures 130 mm high, 101.6 mm wide, and 70 mm deep. Four poles in a single molded case — it's a 4-pole breaker, so it switches all three phases plus neutral (100% N-conductor protection). Front IP40 means it's protected against tools and wires >1 mm, but not against water ingress; mount it inside a panel, not in a washdown zone.