OMRON K8DS-PM2 Relay

OMRON K8DS series slim three-phase voltage + phase-reversal & phase-loss monitoring relays deliver integrated protection for industrial 3-wire three-phase power systems. A single unit monitors four major faults simultaneously: overvoltage, undervoltage, phase loss and phase reversal. Featuring enhanced anti-interference performance against inverters, it supports adjustable wide industrial voltage ranges from 380V to 480V. Adopting a slim 17.5mm standard DIN rail housing, it drastically cuts cabinet installation space. Widely installed on the power supply side of power equipment including three-phase asynchronous motors, water pumps, air compressors and conveyor lines, it prevents equipment damage and production downtime caused by grid abnormalities.

Step-by-Step Model Code Breakdown

Full Model: `K8DS-PM2`

K8DS: Series code for OMRON slim monitoring relays, corresponding to the 17.5mm DIN rail mounting form factor
PM: Function type code, representing combined functions of three-phase voltage monitoring, phase reversal detection and phase loss detection
2: Voltage grade code, matching 3-wire three-phase AC380/400/415/480V input specifications (suffix “1” stands for AC200~240V grade)

Core Technical Specifications

Parameter Category	Parameter Item	Detailed Specifications
Input Characteristics	Rated Input Voltage	3-wire three-phase: AC380V / 400V / 415V / 480V (selectable via rotary switch)
	Input Frequency	Universal for 50Hz / 60Hz
	Rated Input Power Consumption	Approx. 2.8VA
	Voltage Adjustment Range	Overvoltage: -30% ~ +25% of rated value
	Voltage Adjustment Range	Undervoltage: -30% ~ +25% of rated value
	Reset Hysteresis	Fixed at 5% of actuation value, auto-reset mode
Actuation Time	Over/Undervoltage Delay	Continuously adjustable from 0.1s to 30s
	Phase Reversal Detection Time	0.1s ± 0.05s
	Phase Loss Detection Time	≤0.1s
	Power-Up Blocking Time	1s ± 0.5s
Output Characteristics	Output Contact Form	1 changeover contact (1c / SPDT)
	Rated Contact Capacity	AC250V 5A (resistive load); DC30V 5A
	Contact Mechanical Service Life	≥10 million operations
Mechanical & Mounting	Mounting Method	Standard DIN rail mounting
	Unit Width	17.5mm
	Wiring Method	Screw-clamp terminals
	Status Indication	4 LED indicators for Power, Overvoltage, Undervoltage and Fault
Environment & Certifications	Operating Ambient Temperature	-20℃ ~ 60℃
	Storage Temperature	-40℃ ~ 85℃
	Ingress Protection Rating	IP20 (with terminal cover fitted)
	Compliance Certifications	CE, UL, CSA certified

Cross Reference of Same Series Models

Same Function, Different Voltage Grades

Full Model	Rated Input Voltage	Applicable Scenarios
K8DS-PM1	3-wire three-phase AC200/220/230/240V	Low-voltage three-phase systems, supporting imported equipment
K8DS-PM2	3-wire three-phase AC380/400/415/480V	Standard domestic industrial three-phase systems, export machinery

Full K8DS Series Function Comparison

Model	Core Monitoring Functions
K8DS-PH	Phase reversal + phase loss detection only
K8DS-PM	Overvoltage + undervoltage + phase reversal + phase loss
K8DS-PA	Three-phase unbalance + phase reversal + phase loss
K8DS-PU	Undervoltage + phase reversal + phase loss
K8DS-PZ	Overvoltage + undervoltage + three-phase unbalance + phase reversal + phase loss

Typical Application Scenarios

Front-end Protection for Three-Phase Asynchronous Motors: Connected in series to the control circuit of the main circuit contactor for real-time power supply status monitoring. It instantly cuts off the control circuit upon phase loss or phase reversal to avoid motor burnout, ideal for long-running power equipment such as fans, water pumps and air compressors.
Incoming Power Monitoring for Control Cabinets: Mounted at the incoming side of power distribution cabinets to monitor voltage quality of the entire cabinet’s three-phase supply. It outputs alarm signals for overvoltage or undervoltage faults to trigger sound-light alarms or upper monitoring systems.
Front-End Power Protection for Inverters: Designed with enhanced anti-inverter interference capability, it is installed on the input side of inverters to detect grid voltage abnormalities and protect inverter rectifier modules against surges and phase loss damage.
Conveying Systems for Automated Production Lines: Matched with conveyor and roller motor groups to uniformly monitor three-phase phase sequence and voltage, preventing production accidents caused by reversed equipment operation due to wrong phase sequence wiring.
Protection for Central Air Conditioning & Refrigeration Units: Installed in the power supply circuit of compressors for commercial buildings and industrial refrigeration to monitor three-phase power conditions and ensure safe operation of refrigeration compressors.

Common Troubleshooting Matrix

Fault Phenomenon	Root Cause Analysis	Step-by-Step Solutions
Power indicator off, relay no response	1. Missing phase at three-phase incoming lines or loose wiring	1. Measure L1/L2/L3 three-phase line voltages to confirm they fall within the rated 380~480V range
	2. Input voltage out of rated range	2. Tighten terminal wiring and inspect upstream circuit breakers and fuses
	3. Damaged internal power circuit of the module	3. Replace the module for hardware troubleshooting if voltage is normal yet no indicator lights up
Three-phase voltages normal, fault light stays on and output actuates	1. Reversed phase sequence triggers phase reversal protection	1. Verify L1/L2/L3 phase sequence matches terminal marking
	2. Over/undervoltage set thresholds are too low	2. Adjust overvoltage and undervoltage threshold knobs to match actual on-site voltage range
	3. Excessive three-phase voltage unbalance	3. Measure three-phase line voltage differences to eliminate severe unbalance issues
Relay fails to actuate during voltage abnormalities	1. Overlong actuation delay setting	1. Turn down the over/undervoltage delay knob to shorten protection response time
	2. Fault duration shorter than configured delay	2. Check deviation between set thresholds and actual voltage to confirm fault magnitude exceeds actuation limits
	3. Voltage fluctuation fails to reach set threshold	3. Monitor voltage fluctuations with a multimeter to verify protection trigger conditions are met
Relay fails to reset after voltage returns to normal	1. Fault not fully eliminated with latent phase loss/voltage anomalies remaining	1. Continuously monitor three-phase voltages until all phases fully recover and stabilize
	2. Contact adhesion or mechanical jamming	2. Power cycle the unit to test normal relay reset performance
		3. Power off and measure contact continuity to rule out adhesion; replace the module if necessary

Typical Application Scenarios of OMRON K8DS-PM2

As a slim four-in-one three-phase monitoring relay integrating overvoltage, undervoltage, phase loss and phase reversal protection, the K8DS-PM2 is positioned as an economical power protection device for industrial three-phase power loads. Its applications fall into three core categories: three-phase load protection, power quality monitoring, and anti-interference drive matching, detailed as follows:

Front-End Protection for General Three-Phase Power Loads (Most Widely Used)

This is the dominant basic application of the model, providing power-side fault protection for all types of three-phase inductive loads and serving as a direct replacement for traditional single-function phase sequence relays.

Body Protection for Three-Phase Asynchronous Motors

Mounting Position: Connected in series to the coil control circuit of the motor main circuit contactor, or wired to PLC emergency stop interlock input terminals

Core Problems Solved: Overheating and burnout of motor windings from phase-loss operation; mechanical accidents from reversed equipment rotation due to wrong phase sequence; accelerated insulation aging and shortened service life under sustained over/undervoltage

Typical Compatible Equipment: General power equipment including fans, water pumps, air compressors, crushers, machine tool spindles and lifting motors

Application Value: Fast 0.1s-level response for phase loss and phase reversal, directly cutting the control circuit upon faults. Single-unit protection cost is far lower than motor repair and production downtime losses.

Specialized Protection for Industrial Pumps

Mounting Position: Incoming side of electrical control boxes for centrifugal pumps, submersible pumps, screw pumps and other pump equipment

Core Problems Solved: Pump overload burnout caused by phase loss; damaged mechanical seals and bearings plus out-of-control pipeline pressure from impeller reverse rotation due to reversed phase sequence

Typical Applicable Scenarios: Cooling circulation water pumps, chemical process pumps, hydraulic station oil pumps, water supply and drainage pump sets

Application Value: Adjustable 0.1~30s delay avoids false shutdowns from short-term grid voltage sags while guaranteeing reliable actuation under severe faults.

Supporting Protection for Inverter & Drive Systems (Differentiated Advantage Scenarios)

Equipped with enhanced harmonic and electromagnetic interference resistance, the K8DS-PM2 can be directly installed inside inverter cabinets, making it highly suitable for inverter drive applications.

Power Protection on Inverter Input Side

Mounting Position: Main circuit incoming terminals of inverters, DIN rail mounted inside inverter cabinets

Core Problems Solved: Damage to inverter rectifier modules and DC bus capacitors from grid phase loss or sharp voltage surges/drops; false alarms and misoperation of ordinary phase sequence relays under harmonic interference

Typical Applicable Scenarios: Variable-speed fan & pump systems, production line inverter drive systems, air compressor inverter retrofitting projects

Application Value: Tolerates high-order harmonics generated by inverters for stable operation without misactuation, while safeguarding core power components of inverters.

Power Monitoring for Soft Starters & Servo Drive Systems

Mounting Position: Incoming side of soft starters, main power inlet of multi-axis servo control cabinets

Core Problems Solved: Drive failures from instantaneous voltage dips during equipment startup; thyristor burnout of soft starters caused by phase loss

Application Value: Wide voltage tolerance accommodates voltage fluctuations during startup, with a built-in 1s power-up blocking function to prevent false protection triggering at power-on.

III. Industry-Specific Engineering Application Scenarios

Metallurgy & Mining Industry

Power cabinets for belt conveyors and scraper conveyors: Mass monitoring of power supply status for multiple drum motors to prevent full production line shutdown from single motor burnout due to phase loss

Control circuits for ball mills and vibrating feeders: Withstands grid surges and voltage fluctuations generated by startup/shutdown of large plant equipment

Hoist and winch drive systems for mining: Phase reversal protection eliminates risks of reversed lifting direction, complying with mine safety regulations.

Chemical & Pharmaceutical Industry

Agitator motors and metering pump sets for reaction kettles: Ensures stable power supply for continuous production processes, triggering process interlock shutdown upon faults to avoid material scrapping and safety incidents

Purified water & water-for-injection circulation systems: Stable power supply guarantees compliant water quality for pharmaceutical processes and prevents scrapped production batches due to power anomalies

Cabinets for hazardous explosion-proof areas: Compliant with industrial EMC standards, compatible with explosion-proof control cabinets to monitor three-phase power integrity.

Municipal & Water Treatment Industry

Water plant delivery pump houses and booster pump stations: Uniformly fitted to multiple pump units to guarantee uninterrupted urban water supply and fast switchover to standby pumps during faults

Aeration fans and sludge dewaterers in sewage treatment plants: Adapts to voltage drops and mild three-phase unbalance from long-distance power supply within plants

Municipal flood drainage pump stations: Prevents pump equipment failure from phase loss or overvoltage under heavy-load operation in rainy seasons to secure drainage capacity.

Construction & Building Industry

Chilled water units and cooling tower fans of central air conditioning: Protects main compressor motors and avoids damaged valve plates from reversed compressor rotation caused by wrong phase sequence

Fire water pumps and smoke exhaust fans: Meets fire code requirements for terminal power monitoring and ensures reliable operation of fire-fighting loads

Power circuits for elevators and escalators: Monitors supply phase sequence and voltage quality to eliminate safety hazards from power system faults.

Logistics & Automated Production Lines

Roller conveyor and sorting machine motor groups: Unified power monitoring for full production lines to prevent material collision accidents from reversed conveying direction due to on-site wiring phase sequence errors

Stacker and shuttle car systems for automated warehouses: Guarantees reliable power supply to avoid damage to precision logistics equipment from power anomalies

OEM packaging & filling production lines: Slim 17.5mm design fits compact small control cabinets and significantly saves internal cabinet space.

Supporting Equipment for Complete Machinery & Export Projects
Incoming Power Monitoring for MCC / PLC Cabinets

Installed at the power inlet of motor control centers and automated control cabinets to monitor three-phase power status for the entire cabinet. Relay output contacts can be linked with sound-light alarms or upper SCADA systems. Four LED indicators enable on-site rapid identification of fault types (overvoltage / undervoltage / phase loss / phase reversal).

Standard Matching for Export Equipment

Supports four selectable voltage grades (380V/400V/415V/480V) to fit grid standards across China, EU, Southeast Asia, the Middle East and other regions. Fully certified with CE, UL and CSA international approvals to meet export machinery compliance requirements, covering global projects with a single model.

Terminal Protection for Diesel Generator Sets

Mounted on the load output side of diesel generators to monitor output voltage stability and phase sequence, preventing damage to downstream precision loads caused by abnormal generator voltage regulation or reversed phase sequence wiring.