Quick guide to relay selection

Choosing the right relay is something every panel builder, OEM, and machine builder has to get right — yet relay mis-specification is still one of the most common causes of overheating, chatter, premature failure, and unexpected downtime.

In this guide, we break down the essentials of relay selection using real-world engineering experience and referencing Shenler — our chosen relay manufacturing partner and one of the largest relay producers in the world.

1. Start With the Correct Coil Voltage

The coil voltage must match the control voltage of your system, but it also needs to account for voltage stability, inrush characteristics, and the environment.

• DC coils: Better for stable, logic-level control, fast switching, and reduced noise.
• AC coils: More tolerant of voltage variation, ideal for longer cable runs or industrial environments.

If your voltage is likely to dip or fluctuate, choose a coil with an appropriate tolerance window. Shenler provides clear coil voltage ranges across their relay families (e.g., RKE, RFT, RNC, RKL and more).

2. Match the Relay to the Load Type

Contact ratings are not one-size-fits-all. Loads behave differently:

• Resistive loads (R): Straightforward, low inrush.
• Inductive loads (L): Motors, solenoids, contactors — require higher switching performance.
• LED/low energy loads: Can require special consideration due to low current draw and leakage.

Shenler relays follow international standards for AC-15, DC-13 and other load categories, making selection easier.

3. Understand Contact Current Ratings

The nominal current isn’t enough — you must consider:

• Inrush current (which may be 5–10x the rated current)
• Switching frequency
• Expected mechanical vs electrical lifespan

A relay that “looks fine on paper” may fail early if the inrush isn’t accounted for. Shenler provide detailed contact rating curves for every model to avoid this issue.

4. Consider the Environment

Ambient temperature, panel ventilation, humidity, and vibration all impact relay life. Shenler’s liquid-sealed options (suffix LS) are ideal for dusty or high-moisture environments where standard relays may degrade prematurely.

For panels with high thermal load, consider combining Shenler relays with Linkwell filter fans to keep relay coils and contacts within optimal temperature ranges.

5. Don’t Forget the Socket

The relay is only half the story — the socket matters just as much.

• Poor terminal torque can cause arcing and intermittent faults.
• Wrong pin configuration leads to wiring mistakes.
• Lack of accessories (e.g., jumpers, retaining clips) reduces reliability.

Shenler sockets (SKB, SKC, SRC, and SNC series) are designed specifically to pair with Shenler relays, ensuring proper contact pressure, heat dissipation, and mechanical stability.

6. Extra Features That Make a Difference

• LED indicators (suffix L) for quick fault diagnostics
• Test buttons (suffix T) for commissioning and troubleshooting
• Diodes / polarity protection (suffix D or D1) for DC coil protection
• Sealed versions (suffix LS) for harsh environments

Add-ons like these save time and reduce commissioning errors — one of the reasons Shenler relays have become an industry favourite.

Why We Choose Shenler Relays

Shenler is one of the world’s largest relay manufacturers, producing millions of high-reliability industrial relays every year. They have been operating for over 30 years and supply relays to several well-known global brands as the OEM behind the scenes.

Their reputation is built on:

• Extremely consistent manufacturing quality
• Robust testing and certification processes
• Global-scale automation and production capability
• Excellent reliability across inductive and resistive loads
• Long-term component continuity (not constantly changing designs)

At Charter Controls, we have chosen Shenler as our primary relay manufacturer because their quality, consistency, and technical performance match what UK panel builders and machine builders demand.

In short: Shenler relays perform, they last, and they’re trusted by major global brands — and we’re proud to represent them in the UK.

Explore Shenler Relays

You can browse our full range of Shenler relays, sockets, and accessories here:

Shenler Relay Range at Charter Controls

Relay Selection FAQ