What it is and what it does
The Siemens 3VA1020-4ED32-0AH0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection — the workhorse overcurrent device in a distribution panel or motor control center. It's a 3-pole unit rated 20 A continuous, with a TM210 thermal-magnetic overcurrent release (meaning the thermal element handles overloads, the magnetic element handles short circuits). The insulation voltage is rated 800 V, so it's comfortable on 480 V or 600 V class systems. Breaking capacity is where this part earns its keep: 121 kA at 240 V AC, 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at both 500 V and 690 V. Those numbers mean it can interrupt a fault current up to those levels without welding its contacts or venting plasma — critical for high-fault installations like large transformer secondaries or industrial switchboards.
Thermal derating — the real current you get
The breaker carries a full 20 A from 40 °C through 55 °C ambient. At 60 °C it derates to 19 A, and stays at 19 A through 70 °C. That's a tight thermal curve — you don't lose much capacity in a warm panel. If your enclosure hits 70 °C, you're still getting 19 A continuous, not a derate to 16 A like some older designs. The maximum power loss is 12 W, which is reasonable for a 20 A frame.
Panel fit and auxiliaries
Dimensions are 70 mm deep, 76.2 mm wide, 130 mm tall — a 3-inch wide footprint that fits standard panel-mount cutouts. The breaker ships with 2 auxiliary switches plus 1 trip alarm switch (HQ type) already fitted. That's three built-in contacts for status feedback to a PLC or annunciator, no separate accessory kit needed. No undervoltage release, no ground-fault monitoring, no communication module — this is a straight line-protection device, not a smart breaker.