Eaton 15-820-33 Thermal Overload Relay

The Eaton 15-820-33 is a thermal overload relay specifically designed for the protection of small to medium three‑phase AC motors. With an adjustable current range of 2.5 to 4 amperes, it ensures accurate protection against overload, phase loss, and prolonged starting conditions. The relay can be mounted directly onto Eaton contactors (e.g., D25 series) to form a compact motor starter, or used independently with a separate mounting base. It is a reliable and cost‑effective solution for motor control applications.

Key Features

• Adjustable current setting: 2.5‑4 A (calibrated scale on front)

• Class 10 trip characteristic (trips within 10 seconds at 7.2x I_e)

• Phase loss sensitivity: trips within 3 seconds if a phase is lost

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

• Manual/automatic reset selection via switch

• Trip indicator (mechanical flag) for visual status

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

• Stop/test button for functional testing

• IP20 protection for finger‑safe terminals

Technical Specifications

Operating Principle

The relay contains three bimetal strips, each heated by the motor current passing through. When an overload occurs, the bimetals bend and activate a trip mechanism, opening the NC contact in the control circuit, which de‑energizes the contactor coil. In case of phase loss, the remaining phases carry excessive current, causing faster bending and quicker trip. Ambient temperature compensation ensures that the trip curve remains accurate regardless of the surrounding temperature.

Applications

• Protection of small motors in pumps, fans, compressors

• Machine tools and conveyors

• HVAC equipment

• Agricultural machinery

• Packaging machines

Installation and Wiring

The relay can be attached directly to a compatible Eaton contactor using the integrated hook and latch mechanism, ensuring electrical connection between the relay and contactor terminals. For standalone use, a DIN rail adapter (sold separately) can be fitted. Main circuit wiring connects to the top (line) and bottom (load) terminals with clear markings L1, L2, L3 and T1, T2, T3. Auxiliary contacts are accessible via screw terminals on the front.

The Eaton 15-820-33 overload relay provides dependable motor protection in a compact form factor, helping to prevent costly downtime and motor damage.