What this MCCB is and what it does
The Siemens 3VA1120-3GD42-0AA0 is a SENTRON-series 4-pole molded case circuit breaker (MCCB) rated for 20 A continuous, with a TM210 thermal-magnetic overcurrent release. It is designed for line protection — meaning it sits at the feeder or subfeeder level in a distribution panel, not on a motor starter or a specific load. The 75.6 kA interrupting rating at 240 V AC gives it the headroom to clear high-fault currents without upstream coordination issues; at 415 V it still holds 52.5 kA, and at 690 V it drops to 11.9 kA, which is typical for this frame size. The front face carries IP40 protection, so it's fine in a clean indoor panel but not washdown-rated.
Ratings that matter for panel fit
The 20 A rating is flat across ambient temperatures from 40 °C to 55 °C — no derating needed in a warm panel. At 60 °C it drops to 19 A, and at 70 °C it's still 19 A. That's a tight thermal curve, so if your panel ambient runs above 55 °C, you size for 19 A, not 20. The 4-pole configuration means it switches all three phases plus neutral; the neutral pole is switched but not protected (typical for TN systems). Dimensions are 130 mm height, 101.6 mm width, 70 mm depth — standard for the 3VA1 frame, so it mounts on a DIN rail or panel-mount plate without surprises. Maximum power loss is 12 W, which matters for thermal budgeting inside a sealed enclosure.
Coordination and selectivity notes
The TM210 release is thermal-magnetic — fixed thermal pickup for overload, magnetic for short-circuit. No trip indicator, no undervoltage release, no communication module on this variant. If you need selectivity with a downstream 20 A MCB, the MCCB's magnetic trip threshold (typically 10x In for TM releases) should coordinate, but you'll want to verify with the selectivity tables in the 3VA manual. The 800 V rated insulation voltage gives margin for 690 V systems. Storage range is -40 °C to 80 °C, which is wider than the operating range (-25 °C to 70 °C) — that storage spec governs shipping and idle spares, not running conditions.