In modern industrial automation systems, selecting the right relay is critical for ensuring system reliability, electrical safety, and long-term performance. With so many options available, engineers often need to compare multiple relay families before making a decision.
In this guide, we provide a comprehensive comparison of four widely used compact industrial relay series: BETA BMY5, Carlo Gavazzi RMI, Releco C9/C4, and Panasonic HC. We’ll break down their specifications, performance, applications, and help you choose the best relay for your project.
What Is an Industrial Relay and Why Selection Matters
An industrial relay is an electromechanical switching device used to control circuits by opening or closing contacts in response to an electrical signal. These devices are essential in PLC systems, HVAC equipment, automotive testing, telecommunications, and renewable energy systems.
Choosing the wrong relay can result in:
- Contact failure or welding
- Reduced lifespan
- System downtime
- Safety risks
That’s why understanding the differences between relay families is essential.
Overview of the Four Relay Series
1. BETA BMY5 Relay – Versatile General-Purpose Solution
The BMY5 relay is a flexible, general-purpose industrial relay designed for a wide range of applications.
Key Features:
- Contact forms: DPDT, 3PDT, 4PDT
- Current ratings: 3A, 5A, 10A @ 240VAC
- Bifurcated AgNi contacts for improved reliability
- Wide coil voltage range: 6–240V AC/DC
- Optional LED indicator and test button
- PCB or DIN socket mounting
Best For: PLC control, general automation, control panels
2. Carlo Gavazzi RMI – Rugged Industrial Relay
The RMI series is designed for harsher environments and higher electrical stress conditions.
Key Features:
- Contact configurations: DPDT, 4PDT
- Current: 5A or 10A
- Strong insulation (3750VAC coil/contact)
- Wide temperature range (down to –55°C for DC coils)
- Optional LED and surge suppression (RC/MOV)
Best For: Industrial machinery, harsh environments, high inrush loads
3. Releco C9 & C4 – Compact Plug-In Relays
The Releco C9 and C4 series are plug-in relays known for modularity and flexible accessory options.
Key Features:
- 4PDT configuration
- C9: 5A (compact, 14-pin)
- C4: 10A (larger, 16-pin)
- Optional gold-plated contacts for low-level signals
- Multiple accessory modules: LED, diode, RC snubber, bridge rectifier
Best For: Control cabinets, modular systems, easy maintenance setups
4. Panasonic HC – High-Endurance Relay for Demanding Applications
The Panasonic HC series stands out for its exceptional lifespan and environmental resilience.
Key Features:
- Contact forms: 1C to 4C
- Current: up to 10A
- Mechanical life: up to 100 million operations
- Electrical life: up to 20 million operations
- Temperature range: –50°C to +70°C
- High dielectric strength (up to 5000VAC)
Best For: High-frequency switching, telecom systems, harsh environments
Key Specification Comparison
| Specification | BMY5 | RMI | C9 | C4 | HC |
|---|---|---|---|---|---|
| Contact Form | DPDT–4PDT | DPDT/4PDT | 4PDT | 4PDT | 1C–4C |
| Rated Current | 3–10A | 5–10A | 5A | 10A | 5–10A |
| Mechanical Life | 10M | 10M | 10–20M | 10–20M | 50–100M |
| Electrical Life | 100k | 100k | ≥100k | ≥100k | up to 20M |
| Temp Range | –25~+55°C | –55~+70°C | –40~+60°C | –40~+60°C | –50~+70°C |
| Mounting | PCB/Plug-in | PCB/Plug-in | Plug-in | Plug-in | PCB/Plug-in |
Application Comparison
| Application | BMY5 | RMI | C9 | C4 | HC |
|---|---|---|---|---|---|
| PLC I/O | Excellent | Excellent | Excellent | Good | Good |
| HVAC | Good | Good | OK | Good | Good |
| Small Motors | Good | Good | Limited | Strong | Limited |
| Telecom | Good | Good | Good | Overkill | Excellent |
| Automotive Testing | Good | Strong | Moderate | Excellent | Very Good |
| Renewable Energy | Good | Good | Good | Good | Limited |
Reliability and Environmental Performance
- Longest lifespan: Panasonic HC (up to 100 million operations)
- Best for harsh environments: Panasonic HC and RMI
- Best vibration resistance: HC and RMI
- Typical failure modes:
- Contact welding
- Coil burnout
Prevention Tips:
- Use RC snubbers or MOVs for AC circuits
- Add flyback diodes for DC coils
- Keep voltage within ±10% of rated value
How to Choose the Right Relay
Step 1: Check Load Current
- Above 5A → Choose 10A relay (BMY5, RMI, C4) or a contactor
Step 2: Consider Switching Frequency
- High frequency → Choose Panasonic HC
Step 3: Select Coil Type
- DC coil → Add flyback diode
- AC coil → Use RC/MOV suppression
Step 4: Evaluate Environment
- Extreme temperature or vibration → HC or RMI
Step 5: Add Functional Features
- LED indicator for diagnostics
- Test button for maintenance
Step 6: Safety Requirements
- For safety-critical systems → Use certified safety relays (not standard relays)
Simple Relay Selection Flow
Start
│
├─ Load >5A?
│ ├─ Yes → Use 10A relay
│ │ ├─ High duty? → Panasonic HC
│ │ └─ Standard → BMY5 / RMI / C4
│
└─ Load ≤5A
├─ High duty? → Panasonic HC
└─ Standard → BMY5 / RMI / C9Typical Relay Wiring Example
PLC Control Circuit (DC):
24V DC → PLC Output → Relay Coil (+) → Coil (–) → PLC Common
AC Load Circuit:
Line → COM → NO → Load → Neutral
Tip: Always add a flyback diode across DC relay coils.
Final Recommendations
- BMY5 – Best all-around relay with flexible configurations and features
- RMI – Ideal for rugged environments and high surge loads
- Releco C9/C4 – Perfect for modular plug-in systems
- Panasonic HC – Best choice for high reliability and long life
Conclusion
Each relay series has its strengths, and the best choice depends on your application requirements. By considering load current, switching frequency, environmental conditions, and required features, you can significantly improve system reliability and lifespan.
If you’re unsure which relay fits your project, feel free to contact our engineering team for expert guidance.
