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Relay and Optocoupler Applications

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Discover vividly illustrated application examples and learn all about the domains of use and technologies.

Application Examples

Relays with Ex Approval

Safe 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 or in the food industry facilities. 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.

Identifying devices that may be used in hazardous 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 it occurs only momentarily.

Relays for Systems with Long Lines

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

This effect often occurs as a result of 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 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.

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 and replacing old lighting systems, the inrush current of the ECGs must be a central focus.

A capacitor in the input circuit of many ECGs and LED drivers causes a substantial current peak when switched they are on that can well 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?

In the relay selection process, the inrush current must 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 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, conducts 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

Functional safety: To comply with relevant policies and regulations for 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 be clearly identified. Only errors due to opening and isolation failures are important in safety-related matters.

In a circuit, an open break contact can be detected by a closed break contact (error 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-guided. Therefore, only relays with at least two changeover contacts can be used in safety-related circuits.

Harsh Environments – Special Relays

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. 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 for switching larger loads, because smaller 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 to corrosion in adverse conditions.

Relays for Building Automation

Switching manually and electrically: 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 ensuring 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 one hundred switching operations. 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

Versatile: The principle underlying 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 is immediately accessible when replacing 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

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 be allowed to 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.

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

According to the installation location and heat ratio, the rail industry basically 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 (−13 ... 158°F). All WAGO relay modules for railway applications correspond to the highest classes: T3 and 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 Classes	Surrounding Air Temperature outside the Vehicle	Internal Cabinet Temperature	Internal 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 (−13 ... +158 °F)
T2	−40 … +35 °C (−40 ... +95 °F)	−40 … +55 °C (−40 ... +131 °F)	+15 K	−40 … +70 °C (−40 ... +158 °F)
T3	−25 … +45 °C (−13 ... +113 °F)	−25 … +70 °C (−13 ... +158 °F)	+15 K	−25 … +85 °C (−13 ... +185 °F)
TX	−40 … +50 °C (−13 ... +122 °F)	−40 … +70 °C (−40 ... +158 °F)	+15 K	−40 … +85 °C (−13 ... +185 °F)

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 the nominal input voltage range of 5 V to 230 V and nominal output voltage range of 3 V to 280 V.

The integrated protective circuit ensures reliable operation in all applications. The modules switch loads with both inrush and switch-off currents. These include incandescent bulbs with resistive loads and ECGs with capacitive loads (originators of high inrush currents), as well as magnet valves with their inductive coils (originators of burdening switch-off currents).

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 (SSRs) offer the following compelling advantages:

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

Product Overview

Relays and Optocouplers/Solid-State Relays

857 Series

Socket with a Miniature Switching Relay or Solid-State Relay

858 Series

Sockets 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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