Phoenix Contact REL-MR-24DC/21 Single Relay

Technical Overview

Miniature plug-in relay with 24 VDC coil, 1 C/O contact, 6 A continuous, 250 V AC/DC switching, RT III protection, -40°C to 85°C.

Key Features

Safe coil-to-contact isolation tested at 4 kV AC for enhanced circuit protection.
Wide input voltage range (14.4 V DC to 66 V DC) accommodates varying supply conditions.
6 A power contacts with 10 A inrush capacity suit demanding switching loads.
RT III degree of protection supports wash-proof environments depending on type.
Zero-spacing row installation in any mounting position enables high-density panel layouts.
Equipped with a single changeover (SPDT) contact for versatile switching functions.
Operates reliably in ambient temperatures from -40°C to 85°C.
High mechanical service life of 2 x 10^7 cycles ensures long-term durability.

Technical Specification Matrix

Parameter	Value
Nominal Coil Voltage	24 V DC
Input Voltage Range	14.4 V DC to 66 V DC
Contact Type	1 changeover contact (SPDT)
Contact Material	AgSnO (Silver-Tin Oxide)
Limiting Continuous Current	6 A
Maximum Inrush Current	10 A (4 s)
Maximum Switching Voltage	250 V AC/DC
Interrupting Rating (Ohmic Load)	1500 VA (at 250 V AC)
Test Voltage (Winding/Contact)	4 kV AC (50 Hz, 1 min)
Typical Input Current	7 mA at UN
Coil Resistance	3390 Ohm ±10% (at 20°C)
Response Time	5 ms
Release Time	2.5 ms
Mechanical Service Life	2 x 10^7 cycles
Degree of Protection	RT III
Overvoltage Category	III
Pollution Degree	3
Operating and Storage Temperature	-40°C to 85°C
Connection Method	Plug / solder connection
Physical Weight (kg)	0.01
Dimensions L x W x H (cm)	1.5 x 0.5 x 2.8

Industrial Applications

1. Industrial PLC Output Interfacing

This miniature power relay acts as an interposing relay to interface the low-current outputs of a Programmable Logic Controller (PLC) with higher-current industrial loads like motor contactors, solenoids, or indicator lights.

Problem Solved

PLCs often have limited output current capabilities, and directly connecting them to power-hungry loads can damage the PLC outputs. This relay provides the necessary current amplification (6A continuous, 10A inrush) and electrical isolation (4kV AC test voltage) to protect the sensitive PLC electronics from inductive kickback or overcurrents, extending the PLC's lifespan and ensuring robust control.

PLC outputcurrent amplificationelectrical isolationinductive loadcontrol panelmotor contactorsolenoid24V DC control250V AC/DC switching

2. Signal Isolation and Conditioning in Process Control

In process control systems, this relay can be used to safely isolate different voltage domains or to convert control signals. Its wide input voltage range makes it flexible for various 24 VDC nominal control systems, providing a clean, isolated contact for downstream equipment.

Problem Solved

Sensitive analog or digital I/O modules can be susceptible to electrical noise, ground loops, or voltage mismatches when connecting to field devices or other control circuits. The relay's 4kV AC isolation and clean contact switching protect these modules, ensuring signal integrity and preventing damage due to electrical disturbances. Its compact 5mm width allows for high-density installation in crowded control cabinets.

Signal isolationvoltage conversionelectrical noiseground loopprocess controlI/O module protectioncontrol cabinet density24V DC4kV isolationcompact size

3. Harsh Environment Equipment Control (e.g., Washdown Areas)

The relay's RT III degree of protection makes it suitable for control applications in environments where it might be exposed to spray water or other liquids, common in certain industrial sectors.

Problem Solved

In food processing plants, car washes, or other industrial areas requiring frequent cleaning or subject to splashing liquids, standard relays may fail due to moisture ingress. The RT III protection ensures the relay's internal components are safeguarded against such conditions, providing reliable switching for machinery, valves, or pumps in these challenging environments, within its specified -40°C to 85°C operating range.

RT III protectionwash-proofmoisture ingressharsh environmentfood processingindustrial cleaningliquid exposure-40°C to 85°Creliable switching