Phoenix REL-MR/REL-MR-BL Series Industrial Interface Relays Selection Guide

Opening: Compact Plug-in Relays for Industrial Control Circuit Signal Conversion & Load Driving

The Phoenix REL-MR/REL-MR-BL series is a portfolio of high-reliability plug-in industrial interface relays, covering control voltages from 12DC to 230AC, with contact configurations of 21HC (single changeover) and 21-21 (dual changeover), and optional special functions like MS (test button + mechanical indicator), AU (enhanced contacts), and ATEX (explosion-proof certification). Widely used in PLC control systems, solenoid valve driving, and hazardous area equipment control, these relays feature plug-in installation for quick maintenance, high switching capacity (up to 16A), and a wide operating temperature range (-40°C to +85°C), ensuring stable performance in harsh industrial environments. This guide categorizes models by function, decodes nomenclature, and provides scenario-based recommendations for efficient selection.

I. Core Advantages of the REL-MR/REL-MR-BL Series

1. Wide voltage compatibility: Supports 12DC/18DC/24DC/60DC/110DC/24AC/120AC/230AC control voltages, adapting to global industrial control system standards.
2. Flexible contact configurations: 21HC (1NO+1NC single changeover) and 21-21 (2NO+2NC dual independent changeover) meet single/dual load control needs, with a maximum switching current of 16A for heavy-load driving.
3. Diversified special functions:
   • MS: Built-in test button and mechanical position indicator for convenient maintenance and fault diagnosis;
   • AU: Enhanced contact material for extended electrical life and higher load-bearing capacity (suitable for frequent switching);
   • ATEX: Explosion-proof certification for equipment control in hazardous areas (e.g., chemical plants, oil and gas fields).
4. Plug-in design: Enables tool-free quick replacement, reducing equipment downtime by 60% compared to soldered relays.
5. Industrial durability: 10 million mechanical operation cycles, IP20 protection (cabinet-mounted), and anti-vibration construction for factory floor and outdoor auxiliary control scenarios.

II. Product Classification & Detailed Parameter Table

1. REL-MR-BL Sub-series (Blue-Housed Specialized Relays)

With blue housing for visual circuit differentiation, suitable for critical control circuits requiring clear identification.

2. REL-MR Sub-series (Standard General-Purpose Relays)

Covers more voltage types and special functions, suitable for general industrial control and customized scenarios.

III. REL-MR/REL-MR-BL Series Nomenclature Decoding

REL-MR[-BL]-[Control Voltage]/[Contact Configuration]-[Special Features]

• REL-MR[-BL]:
  • REL-MR = Standard general-purpose interface relay;
  • REL-MR-BL = Blue-housed specialized relay (for critical circuit identification).
• Control Voltage:
  • 24DC/24AC = 24V DC/AC (industrial automation standard voltage);
  • 120AC/230AC = Mains voltage (120V for North America, 230V for Europe/Asia);
  • 18DC/60DC/110DC = Special DC voltages (for legacy/custom systems).
• Contact Configuration:
  • 21 = Single normally open (NO) contact (1-pole, 1NO);
  • 21HC = Single changeover contact (1NO+1NC, 1-pole double-throw);
  • 21-21 = Dual independent changeover contacts (2NO+2NC, two 21HC groups).
• Special Features:
  • MS = Test button + mechanical position indicator (maintenance-friendly);
  • AU = Enhanced contact material (higher load capacity, longer electrical life for frequent switching);
  • ATEX = Explosion-proof certification (for Zone 2/Ex I Div. 2 hazardous areas);
  • Omitted = Standard model (no special functions, cost-effective for general scenarios).

IV. 3-Step Quick Selection Technique

Step 1: Confirm Control Voltage Matching the System

• 24V DC PLC control systems: Choose 24DC models (e.g., 2908180 REL-MR-BL-24DC/21HC/MS, 2987888 REL-MR-24DC/21HC/MS) for direct compatibility with PLC outputs.
• 230V AC mains control: Select 230AC models (e.g., 2906288 REL-MR-BL-230AC/21HC, 2987914 REL-MR-230AC/21HC/MS) for workshop lighting/pump control.
• North American 120V AC systems: Opt for 120AC models (e.g., 2987901 REL-MR-120AC/21HC/MS, 2961419 REL-MR-120AC/21HC).
• Special voltage systems (18DC/60DC/110DC): Pick corresponding voltage models (e.g., 2961383 18DC, 2961118 60DC, 2961338 110DC) for legacy/custom equipment.

Step 2: Select Contact Configuration Based on Load Quantity/Type

• Single load control (with feedback): Use 21HC (1NO+1NC) models (e.g., 2906285 REL-MR-BL-24DC/21HC) to realize load driving + status feedback.
• Dual independent load control: Choose 21-21 (2NO+2NC) models (e.g., 2906286 REL-MR-BL-24DC/21-21, 2961451 REL-MR-230AC/21-21) for two separate circuits.
• Simple single-load on/off: Select 21 (single NO) models (e.g., 2961118 REL-MR-60DC/21, 2961383 REL-MR-18DC/21) for cost-effectiveness.

Step 3: Add Special Functions According to Scenario Requirements

• Maintenance-intensive circuits: Add MS (test button + indicator) (e.g., 2908180, 2987888) to simplify fault diagnosis and regular testing.
• High-cycle/frequent switching scenarios: Select AU enhanced contacts (e.g., 2961545, 2961529) to extend relay life by 2-3 times compared to standard models.
• Hazardous areas (chemical/oil&gas): Choose ATEX certified models (e.g., 2906213) to meet explosion-proof safety standards.
• Critical circuit identification: Use REL-MR-BL blue-housed models (e.g., 2906285, 2906288) for visual differentiation from general circuits.

V. Recommended Industry-Scenario Combinations

VI. Selection Pitfall Avoidance Guide

1. Voltage mismatch: 24V DC PLC outputs using 230V AC relays → Confirm system control voltage, select matching 24DC models (e.g., 2908180) to prevent relay burnout and control failure.
2. Contact configuration error: Dual-load control using single-changeover (21HC) relays → Choose 21-21 dual-changeover models (e.g., 2906286) to avoid circuit multiplexing and signal interference.
3. Special function neglect: High-cycle control using standard contacts → Add AU enhanced contacts (e.g., 2961545) to prevent contact ablation and frequent replacement.
4. Hazardous area non-compliance: Explosive environments using non-ATEX models → Select ATEX-certified relays (e.g., 2906213) to meet safety regulations and avoid operational risks.
5. Maintenance convenience oversight: Hard-to-access circuits using non-MS models → Equip with MS test buttons (e.g., 2987888) to reduce maintenance downtime and diagnostic difficulty.
6. Circuit identification confusion: Critical circuits using standard (non-BL) relays → Use REL-MR-BL blue-housed models (e.g., 2906285) for visual differentiation and quick fault location.

Conclusion: Select the Right REL-MR Relay for Industrial Control Stability

The Phoenix REL-MR/REL-MR-BL series provides targeted plug-in relay solutions for industrial control circuits, covering diverse control voltages, contact configurations, and special functions to adapt to PLC systems, mains control, hazardous areas, and high-cycle scenarios.