Relays & Optocouplers in the Application

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Things to Know and Applications

Relays with Ex Approval

Long Lines &
2-Wire Sensors

Lighting Systems

Safe and Flexible

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

Device Identification
It is mandatory to identify the devices for use in hazardous areas.
Potentially explosive areas arise in various applications for example in the chemical industry, during the production of crude oil or natural gas, or 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. WAGO relays are appropriate for use in Zone 2 potentially explosive atmospheres.
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 so-called 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.

Info on 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 and, if one occurs, then only temporarily.

Reliably Switch despite Coupling

To switch on, relay modules require the nominal voltage UN. For operation, however, the holding voltage at only 15% of the nominal voltage is sufficient. In standard circuits, all relay modules operate reliably. In circuits with long, parallel lines, in circuits with active 2-wire sensors or with digital AC control outputs, however, a low holding voltage often leads to malfunction. The modules no longer switch off.

Application example: line capacity (level measurement)Application example: 2-line sensors (parcel load detection)

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 solved?

Long, parallel lines are capacitively coupled to each other. Energy is then transferred to an adjacent conductor. Active 2-wire sensors, such as proximity switches 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 against interference coupling and integrated them into the relay modules. The modules minimize the unwanted voltages at low loss and allow defined switching.

Brief Current Peaks — Fatal Consequences

Equipped with electronic control gear (ECG), modern lights offer numerous advantages. They generate flicker-free light with high levels of efficiency. Both in planning new and replacing old lighting systems, the inrush current of the ECG must be a central focus.

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

What should be considered when planning lighting systems?

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

Things to Know and Applications

Safety-Related Circuits

Small Circuit Loads/ Harsh Environment

Building Automation

Functional Safety

To comply with relevant policies and regulations for functional safety, the use of special components is compulsory.

The EN 50205 standard diff erentiates between two contacts sets by the type of positively driven operation:
Type A: Relay in which all the contacts are mechanically connect Type B: Relays that have both mechanically connected and non-mechanically connected contacts

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 allows errors due to opening failures can be clearly identified. Only errors due to opening and isolation failures are of importance in safety-related matters.

In a circuit, an open break contact can be detected by a closed break contact. 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 per changeover contact, only the break contact or make contact can be used and the changeover contacts must be positively driven. Therefore, only relays with at least two changeover contacts can be used in safety-related circuits.

The contact material is crucial

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.

Contact MaterialApplication Area
AgNi - silver-nickel contact Resistance loads
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 material migration when switching from DC
AgCdO - silver cadmium 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 sliver alloys are prone to oxidation, which leads to an increase in contact resistance. It is not a problem when switching larger loads because ever smaller cleaning electric arcs 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 using hard gold-plated contacts. Gold does not form an oxide layer and is also very resistant against corrosion in adverse conditions.

WAGO has added a relay version with hard, gold plating to the relay portfolio for switching small loads. They are intended for such applications and guarantee reliable signal transmission over a long period.

Switch Manually and Electrically

To switch individual circuits specifically without actuating the controller has a number of tangible advantages in a number of applications, e.g., at start-up.

Application example, building automation

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 to 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 operations. In automatic mode, these modules complete the usual switching operations of the relay.

With 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 the usual switching operations of the relay without limitation.

Things to Know and Applications

Reduce Storage and Service Costs

Rail-Specific Requirements

Durable and Wear-Free


In principle, the relay modules with a wide input voltage range are well-rounded, making them 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 a number of applications, e.g., service and maintenance.

Technicians and maintenance specialists need only one relay module for all voltages that is immediately accessible in the case of error to replace a defective module. 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 need only one relay module as the world standard. For ease of use and reliable electrical connections, WAGO equips the relay modules with push-in CAGE CLAMP® connection technology.

Vibration, Shock and Temperature

Railway systems have two fundamental areas of application: There are the fixed installations in signal boxes, turnout systems and access systems on the one hand. On the other, there are installations in rail vehicles. Of central importance in this area is EN 50155, which differs significantly from traditional industrial standards.

Vibration and Shock: Classification per EN 61373 Vibration and Shock: Classification per EN 61373 Vibration and Shock: Classification per EN 61373
Category Location Description of Device Location
1 Class A M N O
I and J
Components attached directly to or in the vehicle
1 Class B D Components installed in a underfloor cabinet which in turn is attached to the vehicle body
1 Class B K and E Components installed in a large internal cabinet which in turn is attached to the vehicle body
1 Class B F Components as elements of subassemblies installed in a cabinet which in turn is attached to the vehicle body
2 G Cabinets, subassemblies, devices and components attached to the bogie of a railway vehicle
3 H Cabinets, devices and components or assemblies attached to the wheelset of a railway vehicle
Ambient Operating Temperature per EN 50155
External Vehicle Ambient Temperature Internal Cabinet Temperature Internal Cabinet Overtemperature
(< 10 min)
Air Temperature on the PCB
T1 -25 ... +40 C° -25 ... +55 C° +15 K -25 ... +70 C°
T2 -40 ... +35 C° -40 ... +55 C° +15 K -40 ... +70 C°
T3 -25 ... +45 C° -25 ... +70 C° +15 K -25 ... +85 C°
TX -40 ... +50 C° -40 ... +70 C° +15 K -40 ... +85 C°

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 may not cause any damage.

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

Components such as relay modules are exposed to extreme temperatures of -40°C to +70°C in railway applications depending on the area of application. This is because the control cabinet is sometimes installed in steel housings below the passenger compartment that are not climate controlled.

In principle, depending on the place of installation and heat ratio, the railway 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 of -25°C to +70°C. All WAGO relay modules for railway applications correspond to the highest classes of 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 in detail caused by operation.

The WAGO 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.

Optocouplers and Solid-State Relays

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.

Application example: Galvanic isolation, e.g., rev counterApplication example: Signal amplification, e.g., compressed-air valve

There is an extensive portfolio with versions for both DC and AC voltages. They are designed for nominal voltage ranges in the input of 5 V to 230 V and in the output between 3 V and 280 V.

The integrated protective circuit ensures sound operation in all applications. The modules switch loads with inrush and switch-off currents equally. These include incandescent bulbs with resistive and ECG with capacitive load to the originators of high inrush currents, magnet valves with their inductive coils to the originators of burdening switch-off currents.

For areas of application with high switching peaks, WAGO has developed optocouplers and solid-state relays with 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 with the following advantages:

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

Relays and Optocouplers/Solid-State Relays

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Our product specialists will be happy to advise you.

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Phone: 01788 568 008


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