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Basic ConceptsControlElectrical / Electronics SymbolsProtection

Relay Symbols – Electrical and Electronic Symbols

Relays Symbols – Coil, Solenoid, Electromagnet & Contacts Symbols

Relays Symbols

Solenoid operated Relay

Solenoid operated Relay Symbol

The solenoid operated relay has a coil wound around a core that produces magnetic field when the coil is energised by the current flowing through it. The magnetic field pulls the lever (movable contact) to either make or break the contact.

Solenoid Relay with Pushbutton

Solenoid relay with pushbutton Symbol

This relay has a push button instead of a lever. The energized coil pulls in the pushbutton either making or breaking the contact.

Generic Relay

Generic Relay Symbol

A relay is an electrical switch that has a set of control terminal & contact terminals. The control terminals is operated by a single or multiple control signals to swtich the contact terminals. They are used for switching relatively high power circuits using low power signals.

Double Coil Relay

Double Coil Relay Symbol

These type of relays has two coils. Each coil has separate control terminals. Either of the two coils are used for making or breaking contact. When coil 1 is energized, it makes contact while energizing coil 2 breaks the contact. Double coil relay are mostly latching devices whose contacts remains in their position even after de-energizing the coil.

Double coil relay with opposite direction of windings

Double coil relay with opposite direction of windings Symbol

Such type of double coil relay has windings in opposite direction to each other. The magnetic field produced by one coil is opposite to another. Each coil changes the contact position when energized.

Overcurrent Relay

Overcurrent Relay Symbol

Overcurrent relay is a protective relay that activates when the current exceeds a limit to protect the system. It basically isolates the system from the fault current by breaking the contact in between.

Under Current Relay

Under Current Relay Symbol

It is also a current protection relay used to protect system or circuit from low current. It is activated when the current decreases from a specified limit.

Differential Current Relay

Differential Current Relay Symbol

Differential relay operates on the phase difference between the input & output current of a system. If there is any difference that means there is presence of fault current thus it starts switching. They are used for protection of transformers, feeder & motors etc.

Fast Deactivation Relay

Fast Deactivation Relay Symbol

As the name suggests, such type of relays has a very fast deactivation speed. As soon as the power supply is removed from the coil, the coil de-energizes immediately & thus switches the contact.

Slow Excitation Relay

Slow Excitation Relay Symbol

Such type of Relays has a slow operating coil. There is a time delay during the excitation of the coil to switch the contact terminals.

Slow Deactivation Relay

Slow Deactivation Relay Symbol

Such type of relay has a time delay when the power supply is removed from its control terminals. There is capacitor connected in parallel that keeps the coil energized for a specific time depending on its characteristics. After the capacitor discharge, the coil de-energizes & switches the contacts.

Fast Switching Relay

Fast Switching Relay Symbol

This is a fast switching relay that can instantly switch from activated state to deactivated state very fast & vice versa. The coil of such relay energizes or de-energizes as soon as the power supply is applied or removed respectively.  They are used for instant switching applications.

Defective Voltage Relay

Defective Voltage Relay Symbol

Such type of protection relay is activated by defective voltage in line. When there is a voltage fault in the line that could cause damage to the equipment, the relay activates to prevent such damage.

Card Access Relay

Card Access Relay Symbol

This is an electronic relay that operates on special cards. Most card access relays are wireless relays that identify the card & wirelessly passes the signal to the relay to activate or deactivate. These are used for security purposes.

Relay Unaffected by AC

Relay Unaffected by AC Symbol

Such type of Relay coil does not get affected by alternating current.

Differential Relay

Differential Relay Symbol

Differential relays operate on the difference between two electrical quantities. They activates when the specified difference exceeds or decrease a fixed limit. Most differential relays are protective relays used to protect the systems.

Polarized Relay

Polarized Relay Symbol

Polarized relay is a type of relay whose switching depends on the direction of the current flow through the coil. Some relays are magnetically polarized other by using a diode in series with the coil that prevents the current flow in reverse direction.

Magnetically Polarized Relay

Magnetically polarized Relay Symbol

Polarized relay are made up of electromagnetic coil and a permanent magnet. The magnetic flux of the coil distorts the magnetic flux of the permanent magnet to switch the contacts in either position. There are mostly three positions in these relays. Normally it is in neutral position & the direction of the current flow switches it into either of the other two positions.

Electromagnetic Relay

Electromagnetic Relay Symbol

Such type of relay has an electromagnetic coil which is energized by supplying AC or DC current. The coil produces magnetic field which attracts the lever (contact) to make or break contact.

Thermal Relay

Thermal Relay Symbol

Such type of relay operates on the temperature. There is a bimetallic strip that bends when exposed to heat. The heat produce element inside the relay due to heavy current bends the metal strip to break or make the contact. These are used in overload protection for machines.

Solid-State Relay

Solid-State Relay Symbol

Solid-State Relay (SSD) is a type of relay that is made of semiconductors & uses optocoupler to switch the main circuit. It has no moving or mechanical parts so they have more lifespan as the mechanical contacts wear out with switching. There is no switching noise or effect of vibration or movement on its switching.

Stepping Relay

Stepping Relay Symbol

Stepping relay is a type of relay that directs the input current through one of many output terminals using a series of control pulses. The pulses move the contact arm by rotating in steps to connect it one of the multiple output terminals.

Remote Control Relay

Remote Control Relay Symbol

Such type of relays is operated by a wireless remote control. These relays enable the user or any system to operate it without any physical or electrical connection. They relay can switch on/off or switch to one of multiple outputs depending on its type.

Pulse Relay

Pulse Relay Symbol

Pulse relay is a type of latching relay that is activated by a voltage pulse. It retains its position i.e. either OFF or ON until there is a voltage pulse.

Remanance Relay

Remanance Relay Symbol

The remanant or remanance relay is a type of latching relay that retains its position due to the remanance magnetic field in the core. The core is de-energized by current flow in reverse direction.

Intermittent Relay

Intermittent Relay Symbol

Such type of relay has a time delay function. Once activated, Its contacts closes after a fixed amount of time & then reopen it. It repeats the cycle until the power supply is removed.

Solenoid Valve

Solenoid Valve Symbol

The solenoid valve is an electromechanical valve that is used to regulate the flow of any liquid or switch the flow of liquid into other ports. There are different type of solenoid valves depending on current and its mechanism.

AC Relay

AC Relay Symbol

As the name suggest, the coil of such relay is only energized by supplying an AC current. The alternating current produces a varying magnetic field in the coil which results in attracting the contact terminal.

ON/OFF Time Delay Relay

ON-OFF Time Delay Relay Symbol

It is the symbol for representing a relay that has a time delay function for both activation & deactivation. The contacts of such relays turns on & off with adjustable time delay to provide pulses of power. Flashing light are prime example of time delay relay applications.

Mechanical Resonance Relay

Mechanical Resonance Relay Symbol

Such type of relay detects the mechanical resonance in a system & activates when the resonance occurs. Mechanical resonance is the phenomenon when the mechanical frequency becomes equal to the natural frequency of the system. In this case the resonance frequency is 25Hz.

Interlock Relay

Interlock Relay Symbol

Interlock relay is made up of two or more than two coils with individual contacts & the energizing of one coil depends on the contact’s position of the other coils.

Reed Relay

Reed Relay Symbol

The reed relay is made of magnetic contact encapsulated in a tube filled with inert gas. The contacts are enclosed inside an electromagnetic coil. The contact connects when the coil is energized or if there is an external magnetic field. It is very fast & sensitive to low currents but it has very low current & voltage ratings.

Overvoltage Relay

Overvoltage Relay Symbol

Such type of protective relay is used for protection against high voltage. . It is activated when the voltage exceeds from the specified relay voltage limit.

Under voltage Relay

Under voltage Relay Symbol

This is also a protection relay but it activates when the voltage level decreases from a pre specified limit. It protects the circuit from low voltage.

No Volt Relay

No Volt Relay Symbol

Such type of voltage protection relay detects the presence of the voltage. When the voltage supply is removed, it activates. It is used in motor starters to increase the resistance when the voltage is removed so that the motor does not automatically start with low armature resistance (that can damage it).

Distance Relay

Distance Relay Symbol

The distance relay or impedance relay operates on the impedance between the fault in line & its installation point. The impedance is measured by the current & voltage ratings from CT & PT. Once the impedance decreases from the relay impedance limit, the relay activates.

Broken Conductor Protection relay

Broken Conductor Protection relay Symbol

Such type of protection relays are used for detection of broken conductor in a 3 phase power system. It operates on the ratio of Positive sequence current (I1) to negative sequence current. The ratio increases significantly with a broken phase & the relay activates the alarm system.

Under Power Relay

Under Power Relay Symbol

Such type of protective relay keeps the power wattage supply in check. As soon as the power decreases from its threshold it activates to break or make contact.

Short Circuit Protection Relay in Coils

Short circuit protection relay in coils Symbol

This relay detects the short circuit between the turns of coils & activates the protective measure to prevent the systems from more damage.

Reverse Current Relay

Reverse Current Relay Symbol

Such type of relays breaks the contacts when there is a current flow in reverse direction. It is used in DC generators when the voltage of the battery is higher than the generator, the relay disconnects to stop the discharging of battery.

3 Phase Failure Detection Relay

3 Phase Failure Detection Relay Symbol

It is a protection relay used for 3 phase load such as motor or other equipment to prevent it from starting because of damage or burnout during an open phase or failure in any phase.

Overcurrent / Undercurrent Relay

Overcurrent-undercurrent Relay Symbol

Such protection relay is used for protection against low or high current. As long as the current stays in its limit the relay does not activate but as soon as the current crosses any (faulty current) limit the contacts break to protect the circuit.

Motor Stalling Relay

Motor Stalling Relay Symbol

Stalling in motor is a condition when the winding are energized but the rotor does not rotate. During stalling, motor draws huge current that can cause overheating. It is because of heavy load at start or loss of a phase. Stalling relay protects the motor from such condition.

Frequency Relay

Frequency Relay Symbol

This type of relay operates on the frequency of the power system. They are used for detection & protection against abnormal frequencies (under frequency & over frequency) in generators etc. If the frequency exceeds or decreases from the specified limit, it activates to switch the contacts.

Automatic Reclosing Relay

Automatic Reclosing Relay Symbol

Such type of relay can automatically reclose after being open due to a power failure. They are used in power systems where the fault can clear themselves after a failure. If the fault still exists, the relay locks the contacts in open after a few tries.

Overcurrent Relay with Time delay

Overcurrent Relay with Time delay Symbol

Such type of protection relay against current adds in a time delay function. They are used in power system that can handle high current for a short duration of time. If the current remains high for a specified duration, the relay breaks the contact.

Monitoring Relay

Monitoring Relay Symbol

Such type of protection or alarm relay monitor or measure the electrical quantities & protects the circuits against them when they exceeds its limit. The asterisk is replaced with the symbol of that quantity. The types of monitoring relays are over voltage/current, under voltage/current relays etc.

Electromagnet

Electromagnet Symbol

Electromagnet is a wire wounded in a coil around a magnetic core. The current flow through the coil creates a magnetic field which is amplified by the magnetic core. It is used in relays to actuate the contact terminals.

Open Contacts

Open Contacts Symbol

These are the symbols used for representing the open contacts of a relay. It means the contact is break & there is no flow of current

Closed Contacts

Closed Contacts Symbol

These symbols represent closed contacts or make contact. The contacts are short & the current can flow through it.

Normally Open Contact

Normally Open Contact Symbol

This symbol represents the contacts of a relay that are open under no power supply. The circuit is break & there is no current flow. When the relay activates, the contacts are made & it start conduction.

Normally Closed Contact

Normally Closed Contact Symbol

It is the contact of relay that is in closed position when there is no power supplied. the contacts open when the relay activates to break the circuit.

Changeover Contact

Changeover Contact Symbol

This is the changeover contact of a relay that is closed or connected with one terminal (known as normally closed terminal) when the relay is deactivated & the other terminal is open (known as normally open terminal). It changes the contact’s position when the relay activates.

Switch

Switch Symbol

These two symbols represents the switch part of the relay that is used for switching on/off or switching the current from one terminal to another.

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