Electronic Overload Relay
Electronic motor overload protection using current measurement and an algorithmic thermal model.
An electronic overload relay evaluates motor loading from current measurement and a thermal model, providing more precise and broader protection than a conventional bimetal element.
It may support adjustable overload current, selectable trip classes, current unbalance, phase loss, stall, jam, locked rotor, and starting-time supervision.
Advanced versions report motor thermal-capacity utilization, use separate heating and cooling time constants, and inhibit restart until safe thermal conditions are restored.
Selection considers current range, protective functions, measurement method, indication interfaces, and integration with the control system.
Electronic overload relays and digital motor overload protective devices.
Electronic Overload Relay
Dimensions4
External horizontal dimension of the product between its outermost lateral points.
External vertical dimension of the product from its lowest to its highest point.
External distance between the foremost and rearmost surfaces of the product.
Mass of the product itself, excluding transport packaging, additional accessories, and external equipment.
Materials and Finish7
Primary material from which the product is manufactured.
Grade, alloy, class, or technical designation of the product's primary material.
Primary visually perceived colour of the product's external surface.
Designation of the product's primary surface colour according to the RAL colour system.
Type of final surface finish of the product determining its appearance and service properties.
Technological surface treatment applied to modify its protective, mechanical, or decorative properties.
Type of protective, functional, or decorative coating applied to the surface.
Mounting and Installation23
Installation arrangement permitted by the product design, such as wall-mounted, flush-mounted, floor-mounted, or another specified mounting type.
Method used to mechanically secure the product to a support, surface, or load-bearing structure.
Type of surface or supporting base to which the product may be fixed.
Permissible spatial orientation of the component during installation and operation.
Number of holes provided in the product for mechanical fixing.
Diameter of the hole provided for a fixing element used when mounting the product.
Distance between the centres of mounting holes in the horizontal direction.
Distance between the centres of mounting holes in the vertical direction.
Horizontal dimension of the mounting pattern between the outermost fixing points of the product.
Vertical dimension of the mounting pattern between the outermost fixing points of the product.
Size designation of the screw, bolt, or other threaded fastener used for mounting the product.
Designation of the thread provided in the product's mounting holes or fixing elements.
Tightening torque recommended or permitted for fasteners during product installation.
Indicates whether the required fasteners are included with the product.
Indicates whether the design provides for mounting equipment on a DIN rail.
Indicates whether equipment may be mounted directly to the mounting surface without an intermediate DIN rail.
Minimum free space required above the product for installation, cooling, or servicing.
Minimum free space required below the product for installation, cooling, or servicing.
Minimum free space required to the left of the product for installation or servicing.
Minimum free space required to the right of the product for installation or servicing.
Minimum free space required in front of the product for installation and normal operation.
Minimum free space required behind the product for installation and normal operation.
Maximum angle permitted by the manufacturer by which the product may deviate from the specified reference orientation during installation.
Electrical Parameters40
Type of electrical current for which the product's main supply circuit is intended.
Voltage value assigned to the product by the manufacturer for specified application conditions and characteristics.
Operating-circuit voltage with reference to which the product's performance characteristics are specified.
Minimum voltage at which the manufacturer guarantees the intended operating mode of the product.
Maximum voltage at which continuous operation of the product is permitted under the conditions declared by the manufacturer.
AC frequency assigned to the product for normal operating conditions.
Lower limit of the electrical network or signal frequency at which product operation is permitted.
Upper limit of the electrical network or signal frequency at which product operation is permitted.
Current assigned to the product by the manufacturer for the declared operating and thermal conditions.
Current that the product can carry continuously under the manufacturer's declared conditions without exceeding permissible temperature rise.
Voltage with reference to which the product's insulation clearances and dielectric properties are specified.
Peak value of an impulse voltage of specified waveform that the product insulation must withstand without breakdown.
Test voltage applied to verify the dielectric strength of the product insulation.
Minimum permissible insulation resistance between the specified electrically separated parts.
Category characterizing the expected level of impulse overvoltages at the product's point of use.
Degree of pollution of the surrounding microenvironment considered when selecting insulation distances and product characteristics.
Class of protection against electric shock determined by the product design and protective connection method.
Motor technologies and motor types that the product is designed to control, start, protect or drive.
Electrical phase configurations of motors supported by the product.
Minimum motor rated current supported by the product.
Maximum motor rated current supported by the product.
Conductor connection technology used specifically for the main power terminals of the switching device.
Minimum conductor cross-section accepted by the main power terminal.
Maximum conductor cross-section accepted by the main power terminal.
Manufacturer-declared tightening torque specifically for screw, bolt or clamp-type main power terminals.
Conductor connection technology used specifically for the control-circuit terminals.
Minimum conductor cross-section accepted by the control-circuit terminal.
Maximum conductor cross-section accepted by the control-circuit terminal.
Manufacturer-declared tightening torque specifically for a screw-type control-circuit terminal.
Maximum manufacturer-declared voltage that may be switched by the relay-output contacts.
Maximum manufacturer-declared current that may be switched by the relay-output contacts.
Maximum manufacturer-declared active power that may be switched by the relay-output contacts.
Declared number of mechanical operating cycles that the product can perform without electrical switching load.
Declared number of electrical load-switching cycles under the conditions specified by the manufacturer.
Supported methods for connecting the monitored current to the measuring device.
Indicates that the measuring circuit supports connection through an external current transformer.
Indicates that the current transformer ratio used for measurement scaling can be configured in the device.
Minimum configurable primary current value used for current transformer scaling.
Maximum configurable primary current value used for current transformer scaling.
Standard secondary current ratings of external current transformers supported by the measuring input.
Protection and Safety58
Degree of enclosure protection against access to hazardous parts and ingress of solid objects and water, designated by the IP code.
IP degree of protection provided by the accessible front side of the product after its intended installation.
Class of enclosure resistance to external mechanical impacts designated by the IK code.
Indicates whether the declared ingress protection of the enclosure has been verified by certification or testing.
Method or level of protection of the user against direct contact with hazardous live parts.
Minimum adjustable overload current setting.
Maximum adjustable overload current setting.
Smallest selectable increment of the overload current setting.
Standardized overload-relay trip classes supported or selectable by the product.
Minimum declared trip time from the applicable initial condition at 7.2 times the overload current setting.
Maximum declared trip time from the applicable initial condition at 7.2 times the overload current setting.
Indicates that overload tripping characteristics are compensated for ambient temperature.
Minimum ambient temperature within the declared overload temperature-compensation range.
Maximum ambient temperature within the declared overload temperature-compensation range.
Indicates that the motor overload protection characteristic is specifically sensitive to single-phasing or phase-loss conditions through motor-current imbalance or an equivalent protection principle.
Set of protection functions integrated into the product or provided by it in its normal intended configuration.
Reset or restart modes supported after the condition that caused a trip, protection action, alarm or safety stop has been cleared.
Indicates whether the product has a local TEST button for the specified functional check of the device.
Indicates whether a local mechanical or electronic indicator shows that the circuit breaker has tripped protectively.
Minimum configurable motor phase-current unbalance threshold that can initiate protection.
Maximum configurable motor phase-current unbalance threshold that can initiate protection.
Minimum configurable delay before tripping on excessive motor current unbalance.
Maximum configurable delay before tripping on excessive motor current unbalance.
Minimum configurable stall-protection current threshold expressed as a percentage of the relevant motor-current reference.
Maximum configurable stall-protection current threshold expressed as a percentage of the relevant motor-current reference.
Minimum configurable delay before a detected motor stall causes a protective trip.
Maximum configurable delay before a detected motor stall causes a protective trip.
Minimum configurable current threshold for motor jam protection.
Maximum configurable current threshold for motor jam protection.
Minimum configurable delay before a detected motor jam causes a protective trip.
Maximum configurable delay before a detected motor jam causes a protective trip.
Minimum configurable current threshold for locked-rotor protection.
Maximum configurable current threshold for locked-rotor protection.
Minimum configurable delay before locked-rotor protection trips.
Maximum configurable delay before locked-rotor protection trips.
Minimum configurable maximum permitted motor starting time.
Maximum configurable maximum permitted motor starting time.
Maximum permitted or configurable number of motor starts within one hour.
Indicates that motor thermal state is calculated using an internal thermal model.
Indicates that calculated motor thermal-capacity utilization can be displayed, communicated or otherwise reported.
Configurable motor thermal-capacity utilization level at which a warning or alarm is generated.
Minimum configurable motor heating time constant used by the thermal model.
Maximum configurable motor heating time constant used by the thermal model.
Minimum configurable motor cooling time constant used by the thermal model.
Maximum configurable motor cooling time constant used by the thermal model.
Indicates that motor restart can be inhibited after a protection trip until defined restart conditions are satisfied.
Minimum configurable restart-inhibit time after a motor protection trip.
Maximum configurable restart-inhibit time after a motor protection trip.
Indicates whether thermal memory is used by the overload protection algorithm.
Number of independent thermistor sensor circuits evaluated by the protection relay.
Sensor-circuit resistance at which the thermistor protection relay changes to the trip or overtemperature state.
Sensor-circuit resistance below which reset or return from the thermistor trip state becomes possible.
Sensor-circuit resistance below which the thermistor input is interpreted as a short circuit.
Maximum permissible total cold-state resistance of the connected thermistor sensor circuit.
Maximum number of PTC thermistor sensors permitted in series in one sensor circuit where declared by the manufacturer.
Indicates support for a separate thermistor warning or pre-alarm sensor circuit in addition to the trip circuit.
Sensor-circuit resistance corresponding to operation of the thermistor warning or pre-alarm function.
Indicates suitability for direct thermal monitoring of motor or generator windings using embedded temperature sensors.
Environmental Conditions19
Minimum ambient temperature at which normal operation of the product is permitted.
Maximum ambient temperature at which normal operation of the product is permitted.
Minimum ambient temperature permitted during storage of the product while not in operation.
Maximum ambient temperature permitted during storage of the product while not in operation.
Minimum relative air humidity permitted for the declared operating or test condition.
Maximum relative air humidity permitted for the declared operating or test condition.
Temperature at which the corresponding relative humidity value is specified or standardized.
Nature of the humidity conditions for which product operation or resistance is declared.
Indicates whether the permissible humidity value applies only to non-condensing conditions.
Maximum altitude above sea level at which the product may be installed without exceeding the declared conditions.
Indicates whether the permissible product load must be reduced as installation altitude increases.
Altitude above sea level above which the permissible product load must be reduced.
Indicates whether the product's resistance to vibration has been verified under the declared conditions.
Lower limit of vibration frequency applied or permitted in the relevant test.
Upper limit of vibration frequency applied or permitted in the relevant test.
Amplitude or test-method-specified acceleration of vibration applied during product testing.
Indicates whether the product's resistance to short-duration mechanical shocks has been verified.
Maximum acceleration generated during mechanical shock testing of the product.
Duration of an individual mechanical shock pulse during product testing.
Included Equipment10
Indicates whether the product supports installation or connection of specified auxiliary contacts.
Indicates whether one or more auxiliary contacts are included in the standard product configuration.
Number of normally open (NO) auxiliary contacts installed in or supplied with the product.
Number of normally closed (NC) auxiliary contacts installed in or supplied with the product.
Number of changeover auxiliary contacts installed in or supplied with the product.
Indicates whether a local human-machine interface (HMI) is provided for monitoring, configuration, or control.
Indicates whether the product has an integrated local display.
Technology or construction type of the product's integrated display.
Indicates whether the integrated display has a backlight.
Number of integrated LEDs used to indicate product status or operating modes.
Special Features24
Indicates whether current unbalance measurement or calculation is supported.
Number of available digital inputs of the product.
Number of available digital outputs of the product.
Indicates whether user-configurable functions can be assigned to one or more digital inputs.
Indicates whether user-configurable functions can be assigned to one or more digital outputs.
Number of independent relay outputs or sets of switching contacts provided by the product.
Contact configurations provided for the product relay outputs.
Functions permanently assigned or assignable to the product relay outputs.
Number of integrated analogue input channels.
Analogue signal, sensor or resistance input types supported by the product.
Indicates whether the product supports digital data exchange with external devices or systems.
List of supported digital data communication protocols.
List of supported physical or logical digital communication interfaces.
Indicates whether the product can store an internal event log.
Maximum number of event records that can be stored in the product's internal log.
Indicates whether an integrated real-time clock is provided for timekeeping, event time-stamping, or time-based functions.
Indicates whether the product can store a history of protective trips or openings.
Maximum number of protective trip or opening records stored by the product.
Indicates whether measured electrical or other parameters associated with the moment of protective tripping are recorded.
Indicates whether a data-logging function is provided for recording supported measurements, states, or process parameters.
Indicates whether the product stores or provides minimum and maximum values of measured quantities.
Indicates whether the product performs internal diagnostic checks to detect or report internal faults.
Indicates whether a latched trip, fault, or alarm state can be reset remotely through a supported command or interface.
Indicates that warning, fault, status or diagnostic information can be transmitted through a supported digital communication interface.
Standards and Compliance18
Primary normative document or standard according to which the manufacturer classifies or assesses the product.
Additional normative documents and standards declared by the manufacturer as applicable to the product.
Indicates whether an official declaration of conformity is available for the product.
Indicates whether a certificate relating to the declared certification or conformity of the product is available.
Indicates whether the CE marking is applied to the product where applicable.
Indicates whether the UKCA marking is applied to the product where applicable.
Indicates whether the EAC marking is applied to the product where applicable.
Indicates whether the product has a declared UL Listed certification or recognition status.
Indicates whether the product has a declared UL Recognized certification or recognition status.
Indicates whether the cULus mark is applied to the product where applicable.
Indicates whether the manufacturer declares product compliance with IEC 60529.
Indicates whether the manufacturer declares product compliance with IEC 62262.
Indicates whether the product has been tested according to applicable methods of the IEC 60068 series.
Indicates whether product compliance with applicable RoHS restrictions on hazardous substances has been declared.
Indicates whether the manufacturer declares compliance of the product with applicable REACH Regulation requirements.
Indicates whether the product falls within the scope of WEEE requirements for waste electrical and electronic equipment.
Compliance with IEC 60947-4-1 requirements applicable to electromechanical contactors and motor-starters.
Compliance with UL 60947-4-1 requirements applicable to contactors and motor-starters.