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Earth Leakage Relays ELR | Adjustable 30mA-30A | External CT | DIN Rail Mount
Industrial-Grade Factory Direct Supply
KRIPAL manufactures earth leakage relays (ELRs) in the UKE1 series for earth fault detection and protection in low-voltage power distribution systems. The UKE1 works in conjunction with a separate zero-sequence current transformer (ZCT) to detect residual current flowing to earth, and provides an output contact that can trip a circuit breaker, sound an alarm or signal a SCADA system. Available with adjustable sensitivity from 0.03A to 30A and adjustable time delay from 0 to 10 seconds, the UKE1 provides the flexibility to configure earth fault protection for any application from personal protection (30mA) to equipment protection (1-30A) with selective coordination between upstream and downstream devices. The relay features a digital display showing the real-time earth leakage current in amperes, an LED bar graph for at-a-glance leakage level monitoring, and non-volatile memory that stores the last 20 trip events with date/time stamp and the leakage current at the moment of trip. Powered from 230V AC or 24V DC auxiliary supply, the UKE1 is DIN-rail mounted (4-module width) and connects to the ZCT via a shielded twisted-pair cable up to 10 meters in length. Compliant with IEC 60947-2 Annex M for earth leakage relays, KRIPAL UKE1 relays are used with UKM1 MCCBs (via shunt trip) and UKA1 ACBs (via the trip unit input) to add earth leakage protection to any LV circuit breaker.
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How to Select an Earth Leakage Relay
An earth leakage relay is a protection device that detects earth fault current using an external current transformer and provides an output signal to trip a circuit breaker, activate an alarm or log the event to a SCADA system. Unlike an RCCB which integrates the detection and tripping functions in one device, an ELR provides the detection and signaling functions separately from the circuit breaker, allowing earth leakage protection to be added to any circuit breaker (MCCB or ACB) simply by installing the ZCT on the circuit conductors and wiring the ELR output to the breaker’s shunt trip or trip unit input. This selection guide covers the ELR sensitivity range, time delay, ZCT selection, output configuration and integration with the circuit breaker.
UKE1 Earth Leakage Relay Technical Specifications
Sensitivity and Time Delay Configuration
The UKE1 sensitivity is adjustable in 10 steps from 0.03A to 30A via a rotary switch on the front panel, covering the full range from personnel protection (30mA, requiring a dedicated ZCT with high-permeability core) to equipment damage prevention (10-30A for large motors and generators where earth leakage indicates winding insulation degradation). The time delay is adjustable from 0 to 10 seconds, with a choice of definite-time (fixed delay once the threshold is exceeded) or inverse-time (delay decreases as the leakage current increases) characteristics. The inverse-time curve approximates the I squared t heating characteristic of cable insulation, providing faster tripping for higher leakage currents that would cause more rapid insulation thermal damage. For selective coordination, the upstream ELR is set to a higher sensitivity and longer time delay than the downstream device, achieved through the relay settings rather than the circuit breaker trip unit.
ZCT Selection and Installation Guidelines
The ZCT is a separate device, selected based on the sensitivity required and the conductor diameter. For 30mA sensitivity, a ZCT with a high-permeability mu-metal core (initial permeability greater than 50,000) is required to produce sufficient secondary voltage at such a low primary current. For sensitivities of 1A and above, a standard silicon-steel core ZCT is sufficient. The ZCT internal diameter must accommodate all the phase conductors (and neutral if a 4-pole system) with adequate clearance for the conductor insulation. KRIPAL supplies ZCTs in diameters from 35mm (for cables up to 25 sq mm per phase) to 210mm (for multiple 240 sq mm conductors per phase on a 1600A circuit). The ZCT must be installed with all conductors passing through in the same direction, with the conductors centered in the aperture and secured against vibration. The ZCT secondary cable is a shielded twisted pair that must be routed at least 200mm from power cables to avoid electromagnetic interference.
Output Configuration and Breaker Integration
The UKE1 provides two output contacts: a trip contact (1NO, rated 250V AC 5A) that closes when the earth leakage exceeds the set threshold for the set time delay, and an alarm contact (1CO changeover, rated 250V AC 3A) that operates at a user-configurable pre-alarm threshold (typically 50-80 percent of the trip threshold). The trip contact is wired to the circuit breaker’s shunt trip coil (for MCCBs) or to the external trip input on the electronic trip unit (for ACBs), causing the breaker to open on an earth fault. The alarm contact is wired to a panel indicator lamp, a PLC digital input or a SCADA RTU, providing early warning of increasing earth leakage before the trip threshold is reached. The relay includes a manual reset button (front panel) and an external reset input for remote resetting via a pushbutton or SCADA command. After a trip, the relay displays the tripping leakage current value until reset, aiding fault investigation.
Digital Display and Event Logging
The UKE1 front panel features a 4-digit LED display showing the real-time earth leakage current (auto-ranging from 0.1mA to 30.0A), a 10-segment LED bar graph for at-a-glance leakage level monitoring (each segment represents 10 percent of the set trip threshold), and LED indicators for power ON, pre-alarm and trip status. The non-volatile event log stores the last 20 trip events, each recording the date and time (from an internal real-time clock with battery backup), the leakage current at the moment of trip, and the phase currents if the optional current inputs are connected. The event log can be reviewed on the front panel display or downloaded via the RS-485 Modbus communication port (optional) for analysis in the facility’s power monitoring software. This logging capability enables maintenance teams to identify circuits with progressively increasing earth leakage (indicating degrading insulation) and schedule preventive maintenance before a trip occurs.
Specify Earth Leakage Relays for Your Protection Scheme
- ELR and ZCT Selection: Provide your circuit breaker size and earth leakage protection requirements, and we specify the UKE1 model and matching ZCT.
- Integration Drawings: Request wiring schematics for UKE1 connection to UKM1 MCCB shunt trip or UKA1 ACB trip unit input.
- OEM Supply: Source UKE1 relays and ZCTs pre-wired and tested with your MCCB or ACB for plug-and-play switchboard integration.
Applications of Earth Leakage Relays
KRIPAL UKE1 earth leakage relays provide flexible earth fault protection for any low-voltage circuit breaker by adding earth leakage detection and signaling capability to a standard MCCB or ACB. From the 30mA personal protection on a laboratory bench supply to the 10A equipment protection on a 6300A generator incomer, the UKE1 plus ZCT combination provides earth leakage protection at any current level and for any circuit configuration.
Generator Earth Fault Protection
A 2000 kVA standby generator uses a UKE1 ELR with a 210mm ZCT around the generator’s three-phase output cables, set to 5A sensitivity with a 2-second time delay. Generator stator winding insulation degrades over time due to thermal cycling and vibration, and the earth leakage current provides the earliest indication of insulation breakdown before a full phase-to-earth short-circuit develops. The UKE1 trip contact is wired to the generator ACB’s shunt trip, disconnecting the generator from the busbar on an earth fault. The pre-alarm contact (set to 3A, 60 percent of trip) alerts the maintenance team via the BMS to increasing leakage, allowing the generator to be scheduled for winding insulation testing and repair during the next planned maintenance outage rather than suffering an unexpected trip during a grid outage when the generator is required to supply the facility.
Mining Conveyor Motor Earth Fault Protection
A coal mine conveyor system powered by a 500 kW motor uses a UKE1 ELR with a 110mm ZCT around the motor feeder cable, set to 1A sensitivity with a 0.5-second time delay. In mining environments, motor winding insulation is subject to coal dust ingress, vibration and moisture, and earth leakage faults can escalate to phase-to-earth arcing that could ignite methane gas if present. The UKE1 trips the motor feeder MCCB via the shunt trip within 0.5 seconds of detecting 1A earth leakage, faster than the MCCB’s standard overcurrent protection would respond. The UKE1 display allows the mine electrician to monitor the motor’s leakage current trend during weekly inspections, identifying motors with increasing leakage for proactive replacement during scheduled maintenance shifts.
Data Center Power Distribution Earth Leakage Monitoring
A data center uses UKE1 ELRs on the UPS output feeders to each server room PDU, set to 300mA with a 1-second time delay and wired to alarm only (not trip). The 300mA threshold is below the 500mA level at which earth leakage current through cable insulation can cause ignition of surrounding materials, providing fire prevention monitoring. The UKE1 Modbus output reports the leakage current to the DCIM system, which trends the leakage over time and generates a predictive maintenance work order if the leakage increases by more than 50 percent from the baseline, indicating degrading insulation in the PDU transformer or the server power supplies. The alarm-only configuration ensures that a single server power supply developing an earth fault does not trip the entire server room PDU, which would cause a more severe outage than the earth fault itself.
Water Treatment Plant Submersible Pump Monitoring
A water treatment plant uses UKE1 ELRs on each submersible pump feeder, set to 100mA instantaneous for trip and 50mA for pre-alarm. Submersible pump motors are the most common source of earth leakage faults in water industry installations, with water ingress through worn mechanical seals being the primary cause of winding insulation failure. The pre-alarm threshold provides the earliest possible warning of seal degradation (leakage current typically increases from less than 10mA to 50-100mA over several weeks as the seal wears), allowing the pump to be scheduled for seal replacement before the trip threshold is reached and the pump is taken out of service by the protection system.
Port Crane Shore Supply Earth Leakage Protection
Container port quay cranes are supplied via flexible cables from shore supply pillars equipped with UKE1 ELRs, set to 1A with a 0.2-second time delay. The flexible supply cables are subject to mechanical damage from container handling equipment, and a damaged cable can energize the crane structure, creating an electric shock hazard for the crane operator and ground crew. The UKE1 detects the resulting earth leakage current and trips the shore supply MCCB, de-energizing the cable before personnel can contact the energized crane structure. The UKE1 event log records the leakage current at trip, allowing the port electrical engineer to distinguish between a gradual insulation degradation (requiring cable replacement) and a sudden mechanical damage event (requiring inspection of the cable route).
Add Earth Leakage Protection to Your Installation
- Protection Scheme Design: Our engineers design an earth leakage protection scheme with UKE1 relays and ZCTs for every protection level in your installation.
- ZCT Specification: Provide your cable sizes and circuit breaker details, and we specify the correct ZCT diameter and sensitivity.
- OEM Integration: Source UKE1 relays and ZCTs pre-assembled and tested with your switchboard for factory-tested earth leakage protection.
KRIPAL Earth Leakage Relay Manufacturing
KRIPAL earth leakage relays are manufactured in an ESD-protected electronics assembly workshop where the microprocessor-based detection circuit is assembled on surface-mount PCB lines, the summation current transformer interface is calibrated, and the output relay is verified for correct tripping. Each ELR undergoes sensitivity and time delay testing for global earth fault protection in LV and MV distribution systems.
Surface-Mount PCB Assembly and Conformal Coating
ELR printed circuit boards are assembled on automated SMT placement and reflow soldering lines with AOI (Automated Optical Inspection) after soldering. Assembled PCBs are conformally coated with acrylic or silicone coating for protection against humidity and chemical contamination in industrial environments. Coating coverage is verified under UV inspection.
Summation Transformer Interface Calibration
The ELR is calibrated with a reference ZCT (Zero Current Transformer) across the rated sensitivity range. The primary injection current at the trip threshold (adjustable from 30mA to 30A) is verified against the front-panel setting, with calibration data stored in non-volatile memory. Multiple ZCT types with different transformation ratios are supported and verified during calibration.
Time Delay and Output Relay Verification
The adjustable time delay function (0 to 5 seconds, or inverse-time characteristic) is verified by injecting a residual current at 2 times the set threshold and measuring the time to output relay operation. The output relay contacts (volt-free changeover, rated 5A at 250V AC) are tested for contact resistance and dielectric withstand between coil and contacts.
EMC Immunity Testing on Production Samples
Sample ELRs from each production batch undergo EMC immunity testing per IEC 61000-4: electrostatic discharge, radiated RF fields, electrical fast transients, and surge immunity. This ensures that production units maintain trip accuracy in electrically noisy environments such as VFD-driven motor installations and welding shops.
Distributor Stock Holding Programs for Earth Leakage Relays
KRIPAL supports distributor inventory programs with agreed stock levels for standard ELR models with matched ZCTs. Analog dial and digital display versions are available, with shipments planned based on demand data and scheduled replenishment.
Private Label and OEM Branding for Earth Leakage Relays
Custom front-panel overlays with OEM branding, distributor part numbering, and customized instruction manuals are available. Neutral-packaged supply is provided for private label programs.
Multi-Region Certification and Compliance Support
CE, UKCA, and IEC 60947-2 Annex M compliance documentation is provided according to target export markets. EMC compliance certificates to EN 61326-1 are available for all ELR models.
Direct Technical Access to KRIPAL Electronics Engineers
Your technical team communicates directly with the electronics engineers who designed the ELR detection algorithm and hardware. Application questions including earth fault protection coordination with upstream and downstream devices receive answers within 24 hours during China business hours.
Frequently Asked Questions
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