Overload Relay Keeps Tripping? 7 Causes & How to Fix It An overload relay that keeps tripping is protecting a motor from a real, sustained overcurrent condition in almost every case — the relay itself is rarely the problem. Before you swap it out, the two questions worth answering first are: is the relay actually set correctly for the motor's full load current, and is the motor drawing more current than it should be? Get those two right and most "faulty overload relay" call-outs resolve without a single part being replaced. Here are the seven most common reasons a thermal overload relay trips repeatedly, how to tell them apart quickly, and what actually fixes each one — for anyone chasing a nuisance trip on a motor starter rather than a genuine mechanical fault. Never bypass an overload relay to "solve" tripping. Overriding or oversizing it beyond the motor's rating removes the protection it exists to provide and risks burning out the motor winding. Every check below assumes safe isolation and current measurement by a competent person. Talk to Our Expert Team How a Thermal Overload Relay Decides to Trip A thermal overload relay mimics the heating behaviour of the motor windings it protects. Current flowing to the motor also flows through a set of bimetallic strips inside the relay; if that current stays above the relay's set point for long enough, the strips heat and bend, tripping a mechanism that opens the control circuit and drops out the contactor. The relay is deliberately built with an inverse time characteristic — a small overcurrent takes longer to trip than a severe one — because that mirrors how a motor winding actually heats up, and it's what lets the relay tell a brief, harmless starting surge apart from a sustained fault that will genuinely cook the motor. Inverse time trip curve of a thermal overload relay showing trip time falling as current rises above the set point As motor current rises further above the relay's set point, the time to trip falls sharply, mimicking how quickly a motor winding actually overheats. Trip time Current (× set point) 1.0× Never trips (set point) 1.2× 6× Trips in seconds Trips in minutes Overload Relay Terms Worth Knowing Term Meaning F.L.C.Full Load Current — the motor nameplate current the relay should be set to Trip class (10/20/30)Maximum seconds to trip at 7.2× set current — higher class allows longer starting times Single-phasing protectionDetects current imbalance between phases and trips faster than on a balanced overload Reset (manual/auto)Manual reset requires a physical button press; auto-reset re-engages once cool 7 Causes of an Overload Relay Tripping Repeatedly 1 Relay Set Too Low for the Motor's F.L.C. The single most common cause by a wide margin. If the dial is set below the motor's actual full load current — often left over from a previous, smaller motor on the same starter — the relay will trip under completely normal running conditions. Check the motor's nameplate F.L.C. against the relay's current dial setting before assuming anything else is wrong. 2 Genuine Motor Overload From Mechanical Strain A pump fighting a partially blocked line, a conveyor jamming intermittently, or a bearing starting to seize all increase the mechanical load the motor has to work against — and current rises with it. The relay is doing exactly its job here. Measure actual running current against the nameplate F.L.C.; if it's genuinely high, the fix is on the driven machine, not the electrical protection. 3 Single-Phasing on a Three-Phase Motor A blown fuse, a loose terminal, or a failed contactor pole on one phase leaves the motor running on two phases, drawing sharply higher current on the remaining two to try to maintain torque. Most modern overload relays include dedicated phase-loss/imbalance detection specifically because this failure mode is common and destructive if left running. A trip that coincides with unusual motor noise or vibration points here first. 4 Starting Time Longer Than the Relay's Trip Class Allows High-inertia loads — large fans, centrifuges, some pumps — can take longer to accelerate to full speed than a standard Class 10 relay is designed to tolerate, tripping the relay during every start even though the motor and load are both healthy. This calls for a relay rated to a higher trip class (20 or 30), not a higher current setting, since raising the current setting removes real overload protection instead of accommodating the longer start. 5 Frequent Start/Stop Cycling Without Enough Cooldown Thermal overload relays need time to cool between trips, just like the motor windings they're modelling. An application that starts and stops a motor frequently — jogging, inching, or a control system cycling too aggressively — can trip the relay from accumulated heating even if no single start looks abnormal on its own. If the process genuinely needs frequent cycling, an electronic overload relay with a proper duty-cycle rating is a better fit than a basic…