3RU2116-1FB0 | Thermal Overload Relay 3.5 – 5 A, Direct Mounting, Manual Reset, Suitable For S00 Size 3RT Contactor – Siemens

Q: How do I set the 3.5–5 A adjustable range on the 3RU2116-1FB0 for my motor?

A: Turn the setting dial to the motor’s nameplate full-load current (FLC) — the FLC must fall within the 3.5–5 A range of this device. Setting it at the motor FLC (not the maximum of the range) gives correct overload trip timing while still riding through normal starting inrush. If the motor FLC is outside this range, select the adjacent rating in the same series.

Q: Does the 3RU2116-1FB0 provide single-phase (phase loss) protection?

A: Siemens thermal overload relays include single-phase sensitivity: if one phase is lost, the remaining phases carry higher current, causing the bimetal to heat and trip within the specified time. For critical motors, add a dedicated phase-loss relay for faster response independent of load — overload relay phase-loss protection is load-dependent and may take minutes to trip at light load.

Q: How do I set the 3RU2116-1FB0 to protect a motor without causing nuisance trips on starting?

A: Set the thermal overload dial to the motor’s nameplate full-load current (FLC) — ensure the FLC is within the 3.5–5 A range of this relay. For star-delta starters, set the overload relay to 58% of motor FLC (line current in delta = FLC × 0.58). Allow 10 trips for the relay’s thermal memory to stabilise before adjusting the setting.

Q: What is the difference between an Overload Relay and a standard MCB — and why use the 3RU2116-1FB0?

A: A standard MCB protects against overload and short-circuit only. An Overload Relay provides thermal overload protection calibrated to motor FLC, protecting the motor from sustained overloads that would destroy windings before a standard MCB trips. Choose the 3RU2116-1FB0 when the application specifically requires overload relay characteristics.