D curve at 0.3 A — what that means for the circuit
The 5SY4214-8: The D curve means the magnetic trip is set to 10–20 times In (3–6 A), so it handles the high inrush of a small transformer, solenoid valve, or motor starter without nuisance tripping — that is the whole point of the D curve on a 0.3 A frame. The UL1077 listing widens the regulatory acceptance for North American machine builders.
Panel fit — DIN rail space and thermal derating
Depth is 76 mm from the rail surface; the installation depth is 70 mm. The breaker mounts in any position and accepts supply from either end — top or bottom feed, no restriction. The combined terminal top/bottom means the same clamp accepts both the line and load conductor. In a sealed enclosure with a 55 °C internal ambient, the effective continuous current is 0.25 A — the D curve still holds, but the thermal element runs hotter. The surrounding humidity limits are 95 % up to 55 °C, 55 % up to 70 °C, and 35 % at the max 75 °C.
Sourcing and lifecycle — current production
Lifecycle stage is marked as current — this is an active-production part from Siemens, not a phase-out or end-of-life line. If the BOM requires a 2-pole D-curve 0.3 A MCB, this is the direct fit.