Fail-safe DOL starter with integrated safety logic
The Siemens 3RK1308-0CB00-0CP0 is a SIMATIC fail-safe direct-on-line starter built around a 4 via 3DI/LC module — four inputs routed through three digital inputs plus a load-current monitoring channel. It is a single unit that combines a contactor, overload relay, and safety isolation in one 30 mm wide housing that plugs into a base unit. The SCCR matches what you see on larger motor control centers, so it slots into existing coordination studies without rework. Trip Class is adjustable OFF / 5 / 10, letting you match the thermal curve to the motor's start profile. For high-inertia loads like fans or centrifuges, set Class 10; for frequent starts on conveyors, Class 5 keeps the reset time short. Class OFF disables the electronic overload for applications with separate protection.
Safety function and response times
The safe state is load circuit open — the starter drops power to the motor when a safety demand is triggered. ON-delay is fixed at 35 ms; OFF-delay is adjustable 35 to 50 ms, which lets you tune the response for different risk assessments without adding external timer relays. B10d value of 10,100,000 cycles. Safety-related channel count is 1.
Fieldbus and I/O mapping
Dual-protocol onboard — PROFINET and PROFIBUS DP are both supported. Input data mapped to 4 bytes, outputs to 2 bytes. Power supply tolerance is 24 V DC nominal, with a permissible range of 20.4 V to 28.8 V. That covers the sag you see on a long DC bus with multiple starters pulling inrush.
Pluggable into a base unit — no hardwiring of the power section. The module itself is 30 mm wide, 142 mm high, 150 mm deep. Mount vertically or horizontally, but if you go horizontal you need to derate per the manual. Vibration resistance is 2g up to 500 Hz; shock resistance is 6g for 11 ms, which covers most conveyor and pump applications. Minimum load is 50% of smallest adjustable rated current.