Eaton ZB12 Thermal Overload Relay

The Eaton ZB12 Thermal Overload Relay is a bimetallic, phase-loss-sensitive thermal overload relay covering the 0.1 A to 12 A adjustment range, designed to provide reliable and economical motor overload protection when combined with Eaton's DILM contactor series in standard motor starter assemblies. The ZB12 mounts directly onto the lower face of compatible DILM contactors via a snap-on mechanical connection, forming a compact motor starter unit without additional DIN-rail space, terminal wiring, or mounting hardware — a design that significantly reduces panel assembly time and wiring errors. The bimetallic strip elements respond to motor winding heating by deflecting progressively under increasing current, tripping the relay's contact mechanism when the accumulated thermal energy exceeds the setpoint calibrated by the front-panel adjustment dial. This thermal memory effect mirrors the actual heating behaviour of motor windings, providing protection that adapts to partial overload conditions that do not immediately trigger the trip but steadily damage insulation over time if uncorrected.

The ZB12's phase-loss sensitivity is achieved by a differential bimetallic mechanism that detects current imbalance between phases: if one phase is lost, the current in the remaining two phases rises to 1.15× rated value (for a delta-connected motor) or the single-phase current in the broken conductor drops to zero (for star connection), and the asymmetric deflection of the three bimetal strips trips the relay regardless of whether the per-phase current exceeds the overload setpoint. Phase-loss protection is crucial in Saudi Arabia's industrial facilities, where single-phasing caused by blown fuses, loose terminal connections in hot ambient conditions, or overhead line faults is a common cause of motor burnout. The relay provides 1 NC and 1 NO output contacts, supporting both motor circuit lockout (via the NC contact in the contactor coil circuit) and remote alarm or PLC fault indication (via the NO contact). Manual and automatic reset modes are switch-selectable from the relay front face.

In the Saudi Arabian market, the ZB12 is the standard overload relay for small motor starter assemblies in the 0.1–12 A range, encompassing motors from fractional kilowatt to approximately 5.5 kW at 400 V. It is used extensively by SEC-approved panel builders for instrument air compressor auxiliary motor starters, chemical dosing pump panels, small conveyor drive starters, and HVAC fan coil unit motor circuits. Saudi Aramco facilities management contractors and SABIC plant maintenance teams standardise on the ZB12 as a stock item given its direct compatibility with DILM7 through DILM17 contactors and its IEC 60947-4-1 certification. The 50°C ambient rating without compensation adjustment is essential for Saudi Arabia's summer conditions where switchgear rooms in industrial areas can reach 45°C. The relay is also used in standalone operation mounted on a DIN rail adapter for applications where the overload relay must be separated from the contactor.

Razz Middle East maintains comprehensive stock of ZB12 units across the full adjustment range, including the ZB12-4 (2.5–4 A), ZB12-8 (5–8 A), and ZB12-12 (8–12 A) variants, allowing motor-specific selection without ordering special current ranges. All units are supplied with IEC 60947-4-1 datasheets and coordination tables demonstrating Type 1 and Type 2 compatibility with the DILM7, DILM9, DILM12, and DILM17 contactors. We respond to RFQs with SAR pricing within 4 hours and support bulk orders for MCC panel projects across the Kingdom.