Relay and Optocoupler Applications

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Application Examples

Interesting Fact and Applications

Relays with Ex Approval

Relays with Ex Approval

Fast and flexible: Relays from WAGO are suitable for use in Zone 2 explosive atmospheres and thus cover a wide range of applications.

Hazardous Areas

Potentially explosive areas arise in various applications including the chemical industry, during the production of crude oil or natural gas and in the food industry. These are divided into Zones 0, 1 and 2 according to the frequency and duration of occurrence of potentially explosive atmospheres. Relays from WAGO are suitable for use in Zone 2 explosive atmospheres.

Labeling devices that may be used in potentially explosive areas is mandatory.

In order to reduce costs but still be able to install the products in the Ex area, facility operators try to use devices with Zone 2 approval.

A type examination certificate or manufacturer’s declaration is required for use in potentially explosive areas. You can download these from the eShop and add them to your system documentation.

Zone 2

Area in which it is not anticipated during normal operation that a potentially explosive atmosphere will occur as a mixture of flammable materials in the form of gas, vapor or mist with air. If one does occur, then only momentarily.

Relays for Systems with Long Lines

Relays for Systems with Long Lines

Reliable switching despite coupling: To switch on, relay modules require nominal voltage UN. For operation, however, a holding voltage that’s just 15 % of the nominal voltage is sufficient. In standard circuits, all relay modules operate reliably. However, in circuits with long parallel lines, or those with either active two-wire sensors or digital AC control outputs, a low holding voltage often leads to malfunction. The modules no longer switch off.

This effect often occurs when updating systems, changing old “power-hungry” to current “power-saving” relay modules.

What are the causes and how can they be eliminated?

Long parallel lines are capacitively coupled to each other. Energy is then transferred to an adjacent conductor. Active two-wire sensors, such as proximity sensors or level monitors, normally require a minimum continuous current to ensure that the holding voltage is maintained on the relay control lines. Because of this behavior, the relay cannot switch correctly.

For such applications, WAGO has developed specific RC base load modules to protect against interference coupling and integrated them into the relay modules. These modules minimize the unwanted voltages at low loss and allow defined switching.

Lighting Systems and Relays

Lighting Systems and Relays

Brief power spikes, fatal consequences: When equipped with electronic control gears (ECGs) or LED drivers, modern lighting systems offer numerous advantages. They generate flicker-free light with high levels of efficiency. Both in planning new lighting system and replacing old ones, the inrush current of the ECGs is a central concern.

A capacitor in the input circuit of many ECGs and LED drivers causes a substantial current peak when switched on that can far exceed ten times the rated current. Even if the current lasts for just a few milliseconds, it can cause the relay contacts to fuse.

What should be considered when planning lighting systems?

When selecting relays, the inrush current must be considered. Standard relays quickly reach their limits. For such applications, WAGO has developed relay modules with contacts that safely withstand brief high-peak inrush currents. The contact material reliably prevents contacts from catching or fusing.

For maximum inrush currents, relay modules with two contacts working in parallel are available. The first contact, consisting of high-strength tungsten, catches the current peak. The second contact, made of highly conductive silver alloy, manages the operational current.

As an alternative to relays, the WAGO product portfolio includes optocouplers and solid-state relays for use with capacitive loads. Special designs with zero voltage switches minimize the peaks.

Relays in Safety-Related Circuits

Relays in Safety-Related Circuits

Functional safety: To comply with relevant directives and regulations on functional safety, the use of special components is mandatory. These components must meet strict requirements. For relay modules, force-guided contacts with at least one break contact and make contact are required. They must be connected mechanically so that break contacts and make contacts cannot be closed or opened at the same time. This connection allows errors due to opening failures to be clearly identified. Only errors due to opening and isolation failures are important for safety considerations.

In a circuit, an open break contact can be detected by a closed break contact (fault detection). The same applies to a closed make contact when the break contact is open.

Of course, EN 50205 requirements also apply to relays with changeover contacts in safety-related circuits. It stipulates that for each changeover contact, only the break contact or make contact can be used, and the changeover contacts must be force-driven. Therefore, only relays with at least two changeover contacts can be used in safety-related circuits.

Harsh Environments – Special Relays

Harsh Environments – Special Relays

The contact material is decisive: In some sectors of industry, like chemical plants and steelworks, as well as in sewage plants, aggressive gasses are common. Higher pollution levels, as well as high humidity and high temperatures, negatively impact electrical components. These are the domains of application for the various contact materials:

AgNi – silver-nickel contact:

  • Resistance loads
  • Weak inductive loads
  • For middle to high switching power

AgSnO2 – silver tin oxide contact:

  • For high switching loads, primarily in supply voltage applications with high inrush currents
  • Very low tendency to fuse, good burn-off resistance
  • Low material migration when switching from DC

AgCdO – silver cadmium oxide contact:

  • Inductive AC loads
  • For high switching loads, primarily in supply voltage applications
  • Low tendency to fuse, good burn-off resistance

AgNi + Au – silver-nickel contact with hard gold plating

  • Small load range
  • Very corrosion resistant; important material for reliable contact at low switching capacities

The surfaces of the silver alloys are prone to oxidation, which leads to increased contact resistance. This is not a problem when switching larger loads, because small cleaning electric arcs always result. That is not the case for smaller loads. There is not enough energy to break up and clean the oxide layer thermally. This results in malfunctions that can be prevented by using hard gold-plated contacts. Gold does not form an oxide layer and is also very resistant against corrosion in adverse conditions.

Relays for Building Automation

Relays for Building Automation

Manual and electrical switching: Switching individual circuits specifically without actuating the controller is incredibly beneficial for a number of applications, e.g., at startup.

For complex building control systems, individual building systems can be checked and commissioned independently of the controller setup. The same applies to commissioning in industrial processes. When troubleshooting, or to ensure limited manual operation, service and maintenance personnel appreciate the option of manual operation.

Mechanical or electrical manual operation?

WAGO offers two alternatives for the relay modules with manual operation. Version one is designed for front panel manual operation, i.e., the contacts are only closed manually. In manual operation, the modules are limited to approximately 100 switching cycles. In automatic mode, these modules complete the usual switching operations of the relay.

In the second version with manual operation, the relay coil is electrically connected. The operating status can be set via a Manual/Off/Auto switch on the front panel. The relay modules complete typical relay switching operations with no limitations.

Relays with a Wide Input Voltage Range Reduce Costs

Relays with a Wide Input Voltage Range Reduce Costs

Versatile use: The principle behind relay modules with a wide input voltage range makes them well-rounded – perfect for virtually any application. Like the WAGO standard relay modules, they comply with all relevant standards and regulations.

Storage and maintenance costs can also be significantly reduced because one single module covers nearly all standard voltage ranges.

These relay modules are designed for DC and AC voltages from 24 V to 230 V, can connect limiting continuous currents up to 6 A and have the same number of switching cycles as the standard versions. They are recommended for many applications, e.g., service and maintenance.

One Module for Every Application

Technicians and maintenance specialists need only one relay module for all voltages; that way, it is available immediately when they need to replace a defective module. Storing a comprehensive inventory of relay modules for various voltage ranges is no longer necessary.

The “one module for every application” principle also optimizes production and storage for manufacturers with small production runs that are exported internationally. They only need one relay module as the global standard. For ease of use and reliable electrical connections, WAGO equips the relay modules with push-in CAGE CLAMP® connection technology.

Relays for Railway Systems

Relays for Railway Systems

All components used in railway applications must operate reliably at voltages between 70 % and 125 % of the nominal voltage. Brief spikes up to 1.4 times the nominal voltage must not cause any damage.

Deviations from these rules only apply to components powered by stabilized power supplies. Fluctuations of ±10 % of the nominal voltage are permitted – values common for industrial applications.

Relay modules can be exposed to extreme temperatures from −40 to +70 °C (−40 to 158 °F) in railway applications, depending on the area of application. This is because the control cabinet is sometimes installed in a steel housing below the passenger compartment that is not climate controlled.

As a general rule, depending on the place of installation and heat ratio, the railway industry divides the areas of application for electrical components into four temperature classes, from T1 to TX. Experience has shown that a number of applications fall in class T3, which corresponds to the temperature range from −25 to +70 °C (−13 to 158 °F). All WAGO relay modules for railway applications correspond to the highest classes, T3 or TX.

Loads due to vibration and shock are also significant in railway vehicles. EN 61373 “Railway applications – Rolling stock equipment – Shock and vibration tests” describes the mechanical influences caused by operation in detail.

WAGO’s relay modules meet all requirements for use in railway operations in categories 1A to 1B. Due to the spring-loaded connection, they also offer high shock and vibration resistance.

Ambient Operating Temperature per EN 50155
Temperature ClassesSurrounding Air Temperature outside the VehicleInternal Cabinet TemperatureInternal Cabinet Temperature (< 10 min)Air Temperature on the PCB
T1−25 … +40 °C (−13 ... +104 °F)−25 … +55 °C (−13 ... +131 °F)+15 K−25 … +70 °C
T2−40 … +35 °C (−40 ... +95 °F)−40 … +55 °C+15 K−40 … +70 °C
T3−25 … +45 °C (−13 ... +113 °F)−25 … +70 °C+15 K−25 … +85 °C (−13 ... +185 °F)
TX−40 … +50 °C (−13 ... +122 °F)−40 … +70 °C+15 K−40 … +85 °C (−13 ... +185 °F)

Optocouplers and Solid-State Relays

Optocouplers and Solid-State Relays

Durable and wear-free: WAGO has developed a wide range of optocoupler and SSR modules for industrial applications. The optocouplers are directly integrated into the housing for all WAGO optocoupler modules. SSR modules are interchangeable solid-state relays that are PIN compatible with all standard relays.

There is an extensive portfolio with versions for both DC and AC voltages. They are designed for a nominal input voltage range from 5 V to 230 V and nominal output voltage range from 3 V to 280 V.

The integrated protective circuit ensures reliable operation in all applications. The modules handle switching of loads with both inrush and switch-off currents. Causes of high inrush currents include incandescent bulbs with resistive loads and ECGs with capacitive load; causes of burdensome switch-off currents include magnet valves with their inductive coils.

For areas of application with high switching peaks, WAGO has developed optocouplers and solid-state relays with a zero voltage switch. These minimize peaks.

As an interface module between process peripherals, as well as control and signaling equipment, optocouplers and solid-state relays (SSR) impress customers with the following advantages:

  • Long service life
  • No mechanical wear
  • No contact bouncing
  • Short clearing times
  • Low inrush current
  • Silent operation
  • Shock- and vibration-resistance

Product Overview

Relays and Optocouplers/Solid-State Relays

857 Series

Sockets with a Miniature Switching Relay or a Solid-State Relay


858 Series

Socket with an Industrial Relay


859 Series

Rail-Mount Terminal Blocks with Miniature Switching Relay or Optocoupler


788 Series

Sockets with a Miniature Switching Relay


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