Eaton OFT-10W01 Thermal Overload Relay

The Eaton OFT-10W01 is a thermal overload relay specifically designed for the protection of three‑phase AC induction motors in industrial applications. With an adjustable full‑load current range of 7‑10 A, it provides reliable protection against overload, phase loss, and prolonged starting conditions. The relay can be either directly mounted to a compatible Eaton contactor to form a compact motor starter or installed independently on a DIN rail using an optional base.

Key Features

• Adjustable current setting: 7‑10 A (scale marked on dial)

• Class 10 trip characteristic – ideal for standard motor starting

• Phase loss sensitivity: trips within 3 seconds on loss of any phase

• Manual/automatic reset selector (toggle on front)

• Ambient temperature compensation: -5 °C to +40 °C

• Integrated trip indicator (mechanical flag)

• 1 NO + 1 NC auxiliary contacts (rated 5 A, 250 VAC)

• Stop/test button for functional testing without overload

Technical Specifications

Protection Principle

The OFT-10W01 uses a bimetallic strip mechanism that bends when heated by the motor current. The heat generated is proportional to the current squared (I²t) and the duration of the overload. When the bimetals reach a threshold, they trip the relay, opening the NC contact in the control circuit, which de‑energizes the contactor coil. Phase loss causes an imbalance that accelerates tripping, preventing single‑phasing damage. The ambient temperature compensation ensures the trip curve remains accurate even if the surrounding temperature varies.

Applications

• Protection of small motors in pumps, fans, compressors

• Machine tools and conveyors

• HVAC equipment

• Agricultural machinery

• Any application requiring reliable motor overload protection

Installation and Wiring

When mounting directly to a contactor, the relay slides onto the contactor terminals and locks with a spring clip. For DIN rail mounting, an adapter (sold separately) is attached to the relay base. Main circuit wiring connects to the top terminals (line side) and bottom terminals (load side) with clear markings L1, L2, L3 and T1, T2, T3. Auxiliary contacts are accessible via screw terminals on the front.

The Eaton OFT-10W01 combines compact size with robust performance, ensuring long motor life and reduced downtime in industrial environments.