What this MCB is and what it does
The Siemens 5SP3340-3 is a 3-pole SENTRON miniature circuit breaker (MCB) rated 40 A at 400 V AC, 50 Hz, with a 25 kA breaking capacity per EN 60898. Its tripping characteristic E is designed for motor and transformer circuits where inrush currents exceed the B or C curve — it holds through short-duration surges without nuisance tripping, then clears fast on a hard fault. Overvoltage category IV means it's rated for the service entrance, not just downstream subpanels.
Lockout/tagout — this one has it built in
The 5SP3340-3 has an integrated locking slide that accepts a padlock, wire seal, or cable tie. That means positive mechanical isolation — the handle can be locked in the OFF position. No exceptions. If you're specifying for a LOTO program, this saves you from having to add an external lockable handle or a separate disconnect. The switch position indicator shows green for OFF, red for ON — no ambiguity when you're verifying isolation.
Mounting and wiring
Snaps onto a standard 35 mm DIN rail per EN 60715. Takes up 4.5 width units — plan your enclosure fill accordingly. Terminals accept solid or stranded copper from 2.5 mm² up to 50 mm², with saddle terminals for secure clamping. Infeed can be at the box terminal, and the supply cord position is any orientation — no top-feed restriction. Depth is 76.3 mm, height 128 mm. IP40 with conductors connected, so it's suited for dry indoor panels, not washdown zones.
Environmental and mechanical endurance
Rated for ambient temperatures from -25 °C to +55 °C, storage from -40 °C to +70 °C. Survives 30 g shock (11 ms, 3 impacts minimum) and 2 g vibration per IEC 60068-2-6 (20 cycles, 5 to 150 Hz). Surge voltage withstand is 6 kV, insulation voltage 690 V. This is a robust part for industrial panel environments — not just residential.