2-pole, 30 A C-curve — what it means on the line
This 5SJ4230-7HG42 is a 2-pole MCB from the Siemens SENTRON series, with a C-curve trip characteristic and a 30 A rating at 40 °C ambient. The C-curve means it holds through mild inrush — typical for motor starters, contactor coils, and small transformer loads — then trips fast on hard shorts. At 30 A, it's sized for a 7.5 kW motor at 400 V three-phase or a cluster of smaller loads on a subfeed.
DIN-rail fit and panel space
The breaker snaps onto standard 35 mm DIN rail and takes up 36 mm (2 modular width units). Depth is 70 mm — the same as most SENTRON 5SJ4 breakers — so it lines up with adjacent units on the rail. Mounting position is any orientation, which helps when you're packing a tight enclosure.
Temperature derating — what the numbers show
Rated current holds at 30 A up to 40 °C ambient. Above that it steps down: 29.1 A at 45 °C, 28.5 A at 50 °C, 27.8 A at 55 °C, and 27 A at 60 °C. If your panel internal temperature runs warm — say next to a drive or transformer — factor in the derating so the breaker doesn't nuisance-trip on a hot day.
Vibration, sealing, and materials
Rated for vibration up to 50 m/s² at 25–150 Hz and 60 m/s² at 35 Hz (4 sec), so it holds up on machine-mounted subpanels. IP20 with conductors connected, IP40 in the handle area — enough for enclosed industrial use but not washdown. The breaker is sealable, halogen-free, and silicon-free, which matters for food, pharma, or clean-room panels where outgassing or contamination is a concern.