Tag: earth leakage

Why Your LT Panel Keeps Tripping — A Diagnostic Guide for Plant Teams

Short answer: an LT panel trips repeatedly for one of four reasons — a real fault such as insulation failure or earth leakage, protection settings and coordination that do not match the load, genuine overload from equipment added since the panel was designed, or harmonics and leakage current from variable frequency drives. The pattern of the tripping tells you which one you have. Resetting a breaker that has tripped three times in a week is not maintenance; it is postponement. Worse, repeated resetting onto a live fault damages the breaker and whatever lies downstream. Here is how experienced teams narrow it down. Step 1: Record the Pattern Before You Touch Anything Note which device tripped, what was running, the time of day, the weather, and whether any load was starting at that moment. Four or five recorded events usually identify the cause faster than a day of testing. Symptom Pattern Most Likely Cause What to Check Trips only when a motor starts Starting current exceeding the magnetic setting Breaker curve and Ii/Ir settings against motor starting current and starter type Trips during or after rain Moisture ingress and insulation leakage IR values of cables and motor windings, gland sealing, panel IP integrity Incomer trips instead of the faulty feeder Protection discrimination not coordinated Settings study across incomer, bus and outgoing feeders Trips at the same time each day Coincident peak load or a scheduled heavy load Logged demand profile against the panel rating ELCB or RCD trips with no obvious load Cumulative earth leakage, often from VFDs and filters Measured leakage current per feeder, RCD type and sensitivity Trips with heating and discoloured terminals Loose or corroded terminations Thermography scan under load, torque check at terminals Trips as new machines were added Overload — the panel is carrying more than it was designed for Actual load survey against original design load list Step 2: Separate a Real Fault From a Protection Problem A real fault means something downstream has failed: insulation breakdown, a shorted winding, a damaged cable, water in a junction box. A protection problem means nothing has failed, but the device is set to trip where it should hold — or is holding where a downstream device should have cleared the fault first. The test is simple in principle: measure insulation resistance of the outgoing circuits. Healthy insulation plus repeated tripping points at settings, leakage or overload, not at a fault. Step 3: The Coordination Issue Nobody Budgets For Discrimination — the nearest protective device clearing a fault before the one upstream — does not happen by default. It happens when relay and breaker settings are calculated as a system, from the fault level downwards. In plants that have grown over several expansions, the original coordination almost never survives: feeders are added, cables are extended, a transformer is uprated, and nobody revisits the settings. The visible symptom is exactly the one that costs the most: an entire section goes dark because one machine faulted. A protection coordination study, with settings applied and recorded, usually pays for itself in a single avoided shutdown. Step 4: Suspect Harmonics and Leakage in Modern Plants Variable frequency drives, servo drives, UPS systems and switch-mode supplies inject harmonic currents and generate high-frequency earth leakage through their EMC filters. The consequences show up as overheated neutrals and transformers, capacitor bank failures, and RCDs that trip from cumulative leakage with no fault anywhere. The fixes are design-level: correct RCD type and sensitivity, detuned reactors on power factor correction, harmonic measurement, and in some cases filters — not a larger breaker. Step 5: Confirm the Panel Is Still the Right Panel Compare the present connected load against the original load list Check the incoming cable size and transformer capacity against actual peak demand Verify the fault level assumption still holds after any transformer change Inspect busbar temperature rise and ventilation — panels in hot rooms derate Check earthing continuity and measured earth resistance, which degrade quietly over years What a Proper Investigation Delivers A structured investigation ends with a document, not an opinion: thermography report, insulation and earth resistance records, a measured load and leakage profile, a fault level and coordination study, and a settings schedule actually applied to the devices. That record is what prevents the same problem returning after the next expansion. VTPL carries out electrical system studies, protection coordination, panel and distribution upgrades, and corrective works as part of its industrial electrification scope. With 33+ years of electrical EPC experience across 1,000+ projects in 19+ states, our teams work inside live plants for clients in oil and gas, steel, railways and infrastructure — under their safety and shutdown regimes. Frequently Asked Questions Why does my MCCB trip when a motor starts? Usually because the instantaneous (magnetic) setting is below the motor’s starting current, or the starting method produces a higher inrush than assumed. The fix is a correct breaker selection and setting, not a larger breaker. Why does the main incomer trip instead of the faulty feeder? Because protection discrimination has not been coordinated. Settings across incomer, bus coupler and outgoing feeders must be calculated as a system so the nearest device clears the fault first. Why does the ELCB trip during rain? Moisture lowers insulation resistance and increases earth leakage current. Check cable glands, outdoor junction boxes, panel sealing and the insulation resistance of outgoing circuits. Can VFDs cause nuisance tripping? Yes. Drives generate harmonic currents and high-frequency earth leakage through their filters, which can overheat neutrals, fail capacitor banks and trip RCDs with no actual fault present. Is repeated tripping dangerous? Yes. Repeatedly resetting onto a fault damages switchgear contacts and downstream equipment, and masks a developing insulation failure that can lead to an arc event. VTPL provides industrial electrification, protection coordination and distribution upgrade works across India. Losing production to repeated tripping? Talk to our engineering team →