Switching relays

How does a relay work? What different relays are there? Where are relays typically used? Which relay is right for your project? Learn more about switching and controlling circuits here. Switching relays are used in many different applications, for example in automated factories, in vehicles and in household appliances. The switching relays offered by eibabo® are high quality, inexpensive, versatile, reliable and universally applicable. The best-known manufacturers in our range are Wago, Schneider Electric, Bircher, Finder, Grothe, Hima, Issendorf, Metz Connect, Phoenix Contact, Siemens, Tele Hase and Omron.

What are switching relays?

A switching relay is an electromechanical device used to control electrical circuits. It consists of one or more electrical contacts that are controlled by one or more magnetic coils. When the solenoid is activated, the contacts close and current flows. When the solenoid is de-energized, the contacts open and current does not flow.

Source: eibabo®, WAGO 788-312 socket with relayImage: WAGO 788-312 socket with relay

What should be considered when buying a switching relay?

In view of the enormously large selection and the numerous specifications, choosing the right switching relay is not easy. Before you decide on a specific model, you should plan your switching device exactly and define the exact task of the relay. This results in the type of switching relay required. Now select a suitable relay for your project based on the following considerations:

  • Is the installation fixed or moveable? Switching relays for mobile equipment should be able to withstand vibration and shock.
  • What kind of contacts should the relay have? How many? What is the switching current and the switching voltage?
  • Which current magnitudes and voltage magnitudes occur? Consider the nominal voltage of the coil, the coil current, the dropout voltage and pick-up voltage of the coil and resistances.
  • Which response times and release times should not be exceeded?
  • What is the expected switching frequency?
  • What requirements do I place on the service life of the mechanical components?
  • In which environment and in which temperature range is the relay used?

 

How does a switching relay work?

Depending on the design, relays can have a simple or complex structure. However, the basic functional principle is the same. The heart of a relay is the coil with an iron core. When current flows through the coil, an electric magnetic field builds up. A ferromagnetic armature responds and is attracted. This movement connects two contact springs together. The so-called working contacts in the relay close (normally open).

Good to know

Switching relays have electrical ratings for the coil and internal switch contacts. The coil voltage is the voltage required for the coil to operate properly. The circuit voltage rating represents the maximum rating of the switch contacts and should not be exceeded.


In some designs, so-called break contacts are opened when the magnetic field is created. These are called openers. There are combinations of openers and closers, so-called changeover contacts or changeover contacts. As soon as the coil no longer generates a magnetic field, the armature is returned to its initial position by spring force. The working contacts are no longer closed.

In addition, there are numerous other relay types, some for special purposes. As a rule, these relays differ in the functional principle, in structure and size, in the switching capacity and in the contacts. A few examples briefly explained:

  • For example, thermal relays use a bimetallic strip that bends when heated, opening or closing the contacts. Thermal relays are commonly used in circuit breakers.
  • Photoelectric relays respond to light pulses and open or close the contacts accordingly. These are used, for example, in photo flash devices and surveillance systems.
  • In static relays there are no moving contacts. The switching action is triggered by thermionic valves, transistors or amplifiers.

 

This list could be continued, for example with time delay relays, solid state relays, coupling relays, distance relays, differential relays, undervoltage relays or overvoltage relays. There are separate categories for many of these special shapes here in the eibabo® shop. Please use our intelligent search.

What are switching relays used for?

Relays allow a low current circuit to control or switch one or more higher current circuits. Switching relays in a variety of designs are required in electrical distribution and electrical installation. The switching relays from our shop can be used for all interface applications in demanding control systems. This allows you to connect highly sensitive and almost powerless controls of a PLC, a control system or a process computer with the power level of a machine or another connected consumer.

What are the advantages and disadvantages of switching relays compared to other switching mechanisms?

Switching relays offer the following advantages:

  • Switching relays are inexpensive.
  • The components are robust and tolerate voltage peaks and current peaks.
  • Switching relays provide potential-free isolation from the load circuit.
  • The heat development is low. Cooling is not necessary.
  • Switching relays switch both very low signals and high-frequency power.
  • In many cases, the current switching status can be seen with the naked eye.
  • Thinner gauge wire can be used to connect the control switch to the relay.
  • Relays make it possible to direct current to a device via the shortest path. This reduces voltage losses.

 

 


TIP:

Semiconductors, semiconductor circuits or transistors are used as an alternative to relays. These offer an extremely fast response time.


 

However, switching relays also have disadvantages:

  • The mechanical components are subject to a certain amount of wear.
  • Switching relays react sensitively to shocks and mechanical loads.
  • The switching actions are audible.
  • The response times and fall times are very long compared to semiconductors.
  • The insulating capacity often depends on the environmental conditions.

 

Why are protective devices used on some switching relays?

If a relay is switched off and the coil suddenly loses current, a large voltage spike can occur. For this reason, protective mechanisms such as resistors or diodes are switched across the coil of the relay. These reduce or prevent the risk of these voltage peaks flowing back into the control circuit and damaging sensitive components. Resistors last longer, diodes provide more efficient protection against voltage spikes. You can judge what kind of protection is required based on the sensitivity of your components in the connected circuit.

Why doesn't my switching relay switch off anymore?

When choosing the right relay, you should pay attention to the loads that occur. Current peaks when switching can cause the contacts to 'stick' or 'weld' together. If the relay is not designed for the loads that occur, the surfaces of the contact springs will change over time. This can result in the contacts no longer opening when the relay is de-energized. Conversely, loads that are too low can also lead to a similar effect, since the self-cleaning process no longer takes place.

 

eibabo - technology store

 

Catalogue content:


In this eibabo® catalogue Relays > Switching relay you will find items from the following product groups:

Item overview:

  • AC contactor
  • Bracket mount
  • Built-in relay
  • Changeover relay
  • Closer
  • Complete relay
  • Coupling module
  • DC voltage relay
  • Inrush voltage
  • Installation relay
  • Manual control level
  • Miniature relay
  • Mounting clip
  • Plug-in relay
  • Power relay
  • Railway relay
  • Relay coupler
  • Relay interface module
  • Relay socket
  • Relay switch
  • Relay terminal
  • Remote switching relay
  • Single relay
  • Switch module
  • Toggle relay
  • Transfer blocks
  • Universal relay
  • Window drives


from the following manufacturers:

Manufacturer overview catalogue Switching relays:

  • ABB
  • Albright
  • Bircher
  • Comat
  • Dold
  • Finder
  • Glen Dimplex
  • Grothe
  • Hima
  • Indexa
  • Legrand SEKO
  • Lütze
  • Metz
  • Murrelektronik
  • Omron
  • Phoenix
  • Rockwell
  • Schalk
  • Schneider Electric
  • SHC
  • Siemens
  • Tele
  • TTI
  • WAGO
  • Weidmüller
  • Wieland


 
How does a relay work? What different relays are there? Where are relays typically used? Which relay is right for your project? Learn more about switching and controlling circuits here. Switching... read more »
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Switching relays - tips and information before you buy

How does a relay work? What different relays are there? Where are relays typically used? Which relay is right for your project? Learn more about switching and controlling circuits here. Switching relays are used in many different applications, for example in automated factories, in vehicles and in household appliances. The switching relays offered by eibabo® are high quality, inexpensive, versatile, reliable and universally applicable. The best-known manufacturers in our range are Wago, Schneider Electric, Bircher, Finder, Grothe, Hima, Issendorf, Metz Connect, Phoenix Contact, Siemens, Tele Hase and Omron.

What are switching relays?

A switching relay is an electromechanical device used to control electrical circuits. It consists of one or more electrical contacts that are controlled by one or more magnetic coils. When the solenoid is activated, the contacts close and current flows. When the solenoid is de-energized, the contacts open and current does not flow.

Source: eibabo®, WAGO 788-312 socket with relayImage: WAGO 788-312 socket with relay

What should be considered when buying a switching relay?

In view of the enormously large selection and the numerous specifications, choosing the right switching relay is not easy. Before you decide on a specific model, you should plan your switching device exactly and define the exact task of the relay. This results in the type of switching relay required. Now select a suitable relay for your project based on the following considerations:

  • Is the installation fixed or moveable? Switching relays for mobile equipment should be able to withstand vibration and shock.
  • What kind of contacts should the relay have? How many? What is the switching current and the switching voltage?
  • Which current magnitudes and voltage magnitudes occur? Consider the nominal voltage of the coil, the coil current, the dropout voltage and pick-up voltage of the coil and resistances.
  • Which response times and release times should not be exceeded?
  • What is the expected switching frequency?
  • What requirements do I place on the service life of the mechanical components?
  • In which environment and in which temperature range is the relay used?

 

How does a switching relay work?

Depending on the design, relays can have a simple or complex structure. However, the basic functional principle is the same. The heart of a relay is the coil with an iron core. When current flows through the coil, an electric magnetic field builds up. A ferromagnetic armature responds and is attracted. This movement connects two contact springs together. The so-called working contacts in the relay close (normally open).

Good to know

Switching relays have electrical ratings for the coil and internal switch contacts. The coil voltage is the voltage required for the coil to operate properly. The circuit voltage rating represents the maximum rating of the switch contacts and should not be exceeded.


In some designs, so-called break contacts are opened when the magnetic field is created. These are called openers. There are combinations of openers and closers, so-called changeover contacts or changeover contacts. As soon as the coil no longer generates a magnetic field, the armature is returned to its initial position by spring force. The working contacts are no longer closed.

In addition, there are numerous other relay types, some for special purposes. As a rule, these relays differ in the functional principle, in structure and size, in the switching capacity and in the contacts. A few examples briefly explained:

  • For example, thermal relays use a bimetallic strip that bends when heated, opening or closing the contacts. Thermal relays are commonly used in circuit breakers.
  • Photoelectric relays respond to light pulses and open or close the contacts accordingly. These are used, for example, in photo flash devices and surveillance systems.
  • In static relays there are no moving contacts. The switching action is triggered by thermionic valves, transistors or amplifiers.

 

This list could be continued, for example with time delay relays, solid state relays, coupling relays, distance relays, differential relays, undervoltage relays or overvoltage relays. There are separate categories for many of these special shapes here in the eibabo® shop. Please use our intelligent search.

What are switching relays used for?

Relays allow a low current circuit to control or switch one or more higher current circuits. Switching relays in a variety of designs are required in electrical distribution and electrical installation. The switching relays from our shop can be used for all interface applications in demanding control systems. This allows you to connect highly sensitive and almost powerless controls of a PLC, a control system or a process computer with the power level of a machine or another connected consumer.

What are the advantages and disadvantages of switching relays compared to other switching mechanisms?

Switching relays offer the following advantages:

  • Switching relays are inexpensive.
  • The components are robust and tolerate voltage peaks and current peaks.
  • Switching relays provide potential-free isolation from the load circuit.
  • The heat development is low. Cooling is not necessary.
  • Switching relays switch both very low signals and high-frequency power.
  • In many cases, the current switching status can be seen with the naked eye.
  • Thinner gauge wire can be used to connect the control switch to the relay.
  • Relays make it possible to direct current to a device via the shortest path. This reduces voltage losses.

 

 


TIP:

Semiconductors, semiconductor circuits or transistors are used as an alternative to relays. These offer an extremely fast response time.


 

However, switching relays also have disadvantages:

  • The mechanical components are subject to a certain amount of wear.
  • Switching relays react sensitively to shocks and mechanical loads.
  • The switching actions are audible.
  • The response times and fall times are very long compared to semiconductors.
  • The insulating capacity often depends on the environmental conditions.

 

Why are protective devices used on some switching relays?

If a relay is switched off and the coil suddenly loses current, a large voltage spike can occur. For this reason, protective mechanisms such as resistors or diodes are switched across the coil of the relay. These reduce or prevent the risk of these voltage peaks flowing back into the control circuit and damaging sensitive components. Resistors last longer, diodes provide more efficient protection against voltage spikes. You can judge what kind of protection is required based on the sensitivity of your components in the connected circuit.

Why doesn't my switching relay switch off anymore?

When choosing the right relay, you should pay attention to the loads that occur. Current peaks when switching can cause the contacts to 'stick' or 'weld' together. If the relay is not designed for the loads that occur, the surfaces of the contact springs will change over time. This can result in the contacts no longer opening when the relay is de-energized. Conversely, loads that are too low can also lead to a similar effect, since the self-cleaning process no longer takes place.

 

eibabo - technology store

 

Catalogue content:


In this eibabo® catalogue Relays > Switching relay you will find items from the following product groups:

Item overview:

  • AC contactor
  • Bracket mount
  • Built-in relay
  • Changeover relay
  • Closer
  • Complete relay
  • Coupling module
  • DC voltage relay
  • Inrush voltage
  • Installation relay
  • Manual control level
  • Miniature relay
  • Mounting clip
  • Plug-in relay
  • Power relay
  • Railway relay
  • Relay coupler
  • Relay interface module
  • Relay socket
  • Relay switch
  • Relay terminal
  • Remote switching relay
  • Single relay
  • Switch module
  • Toggle relay
  • Transfer blocks
  • Universal relay
  • Window drives


from the following manufacturers:

Manufacturer overview catalogue Switching relays:

  • ABB
  • Albright
  • Bircher
  • Comat
  • Dold
  • Finder
  • Glen Dimplex
  • Grothe
  • Hima
  • Indexa
  • Legrand SEKO
  • Lütze
  • Metz
  • Murrelektronik
  • Omron
  • Phoenix
  • Rockwell
  • Schalk
  • Schneider Electric
  • SHC
  • Siemens
  • Tele
  • TTI
  • WAGO
  • Weidmüller
  • Wieland
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