Relays designed to operate with AC input.
Sometimes used for Contact Separation or for Magnetic Air Gap.
Hinged or pivoted moving part of the magnetic circuit of an electromagnetic relay. Sometimes used in a general sense to means any moving part which actuates contacts in response to a change in coil current.
Sometimes used for Movable Contact.
A relay operated by an electromagnet which, when energised, causes an armature to be attracted to a fixed pole (or poles).
A relay, which operates in response to opening and closing of its operating circuit to assist another relay or device in performance of a function. for example a measuring relay, for the purpose of providing higher rated contacts or introducing a time delay.
An arc that transfers contact material from the anode side to the contact surface on the cathode side.
The problem where contact surfaces become dirty and discharge occur more easily.
Note: If precious metal contacts switching in an environment with certain types of organic gases present, the organic gas that attaches to the surface of the contacts will break down as a result of the discharge and create black powder (e.g., carbon), which makes discharge more likely to occur.
BBM (Break Before Make) contacts (Non-shorting contacts)
BBM contacts are part of the group of contacts that have a specified operating sequence. BBM contacts are a set of contacts in which the contacts that should open at operation open before closing the contacts that need to close. Contacts which interrupt one circuit before establishing another.These are called transfer contacts.
Same as Normally Closed Contacts. Sometimes used for the stationary contact of single-pole normally closed contacts
The part of a relay, which limits movement of the armature away from the pole piece or core.
Supplementary relaying designed to operate if a primary relay should malfunction or a circuit breaker fails to operate. Backup relaying usually disconnects more of the power system than just the part with the faulty element as this is necessary in order to remove the abnormal condition and to minimize effect on the remainder of the system.
A protective system intended to supplement the main protection in case the latter should be
ineffective, or to deal with faults in those parts of the power system that are not readily included
in the operating zones of the main protection.
A relay so designed that a bar actuates several contacts simultaneously.
A relay in which the characteristics are modified by the introduction of some quantity other than
the actuating quantity, and which is usually in opposition to the actuating quantity.
Same as Back Contact,
Sometimes used for Release Time.
Intermittent switching between contacts due to shock and vibration caused by the impact of the moving parts of relays (armatures) colliding with the core or other contacts (JIS C5442).
Undesirable intermittent switching that occurs between contacts when they are turned ON or OFF. The time that this intermittent switching continues is called bounce time.
Carbon generated by the electrical switching operation of contacts that attaches to the surface of contacts and causes activation.
A brown or black-brown organic compound in powder form that is created by the reactions of organic gases on contact surfaces.
Bridging is a term used to describe a contact transfer in which the movable contact touches the normally open contact before leaving the normally closed contact during the transfer action, thus never completely opening the circuit of the movable contact.
Sometimes used for Wiper.
The loading imposed by the circuits of the relay on the energizing power source or sources,
expressed as the product of voltage and current (volt-amperes, or watts if d.c.) for a given
condition, which may be either at ‘setting’ or at rated current or voltage. The rated output of
measuring transformers, expressed in VA, is always at rated currant or voltage and it is important,
in assessing the burden imposed by a relay. to ensure that the value of burden at rated current
Insulation between live parts, for basic protection against shock current. (VDE 0110-1:1997, section 18.104.22.168)
Bath Tub Curve
Profile of the failure rate function of the main influencing factor (eg, time, cycles, etc.). This course can genernally be divided into three main areas.
· Early failures: Here, the failure rate has a downward trend.
· Random failures: In this area, the failure rate is constant; this area is called "service life".
· Wear-out failure: where the failure rate increases as a result of wear and tear.
The burn-off is a loss of material at the contacts caused by electric arcs while switching.
The angle between the vectors representing two of the energizing quantities applied to a relay
and used for the declaration of the performance of the relay.
The curve showing the operating value of the characteristic quantity corresponding to various
values or combinations of the energizing quantities.
A quantity, the value of which characterizes the operation of the relay, for example, current for
an overcurrent relay, voltage for a voltage relay, phase angle for a directional relay, time for an
independent time delay relay, impedance for an impedance relay.
Characteristic impedance ratio (C.I.R.)
The maximum value of the System Impedance Ratio up to which the relay performance remains within the prescribed limits of accuracy
A sustained rapid opening and closing of contacts caused by variations in the coil current, mechanical vibration and shock or other causes.
Check protective system
An auxiliary protective system intended to prevent tripping due to inadvertent operation of the main protective system.
Sometimes used for Armature Relay.
Sometimes used for Marginal Relay.
An arc that transfers contact material from the cathode side to the contact surface on the anode side.
The problem where the contact resistance drops dramatically for contacts that make contact through a contact film, because the contact voltage has exceeded a certain value causing that film to be electrically damaged.
A magnetic or thermal winding to which energy is supplied to activate the relay.
A magnetic body inserted in the coil to effectively operate the magnetomotive force in an electromagnet.
Coil resistance is the resistance between coil terminals when the coil temperature is 23°C.
Coil inductance (listed for general relays only)
For DC relays, the value found from the time constant by adding rectangular waves. For AC relays, the value at the rated frequency. The values are different for operation and release.
Current-carrying ports of a relay, which engages or disengages to make or break electrical circuits.
Contact arrangement refers to the combination of different basic contact forms to make up the entire relay switching structure.
Uncontrolled making and breaking of contact when relay contacts are moved to the closed position.
The distance two contacts travel together after just touching.
The gap between a set of contacts when they are open.
Note: This is the shortest distance between two conductors that make up the contacts. Same as Contact Separation.
Springs for adding contacting force to the contact's contacting section.
A current-carrying spring to which contacts are fastened.
Each movable contact of a relay constitutes a pole of the relay.
A combination of stationary contact and a movable contact which are engaged when the coil is unenergised is referred to as back, break, form B, or normally closed contacts and is abbreviated NC.
A combination of stationary contact and movable contact, which are engaged when the coil is energised is referred to as front, make, form A, or normally open contacts and is abbreviated NO.
A combination of two stationary contacts and a movable contact which engages one of them when the coil is energised and engages the other when the coil is unenergised is called transfer, form C, or double-throw contacts and is abbreviated DT. Contrasted with double-throw contacts, NO and NC contacts are called single-throw contacts, abbreviated ST.
A combination in which a movable contact simultaneously makes and simultaneously breaks connection between two stationary contacts is called double-break contacts and is abbreviated DB.
For normally open contacts, this combination may be called double-make contacts.
Relay contact notations are given in the following order:
3. Normal Position
4. DB, if double-break or double-make contacts
Examples: SPST NO DB designates single-pole, single-throw, normally open, double-break contacts.
All contacts are single break except when noted as double-break (DB). Relays having several sets of differently functioning contacts will have the contact forms listed in alphabetical order of their letter symbols. Example: 1A2B refers to SPST NO contacts and DPST NC contacts.
For a relay on which the moving contact engages more than two stationary contacts during its cycle of operation, the contact arrangement is described as MPNT, where M is the number of poles and N is tile number of throws, e.g., 8P 20T.
Contact Over travel
Sometimes used for Contact Follow.
Maximum distance between mating relay contacts when the contacts are in the open position.
Contact resistance is a combination of the inherent resistance of the conductors that make up the armature, terminals, contacts, etc., the boundary resistance where two contacts meet, and the concentrated resistance.
The wear of contacts due to mechanical causes, such as wear during repeated operation.
The expending of contacts due to electrical, thermal, chemical, and other causes during the repetition of contact switching.
Metal oxides, sulfides, and other film that is generated on or attaches to contact surfaces and cause boundary resistance.
Contacts made from two or more layers of different materials.
Sometimes used for a relay with heavy-duty contacts.
Same as Make-before-break Contacts.
A relay, which may be energised with, rated coil voltage or current at rated contact load for a period of 3 hours or more without failure and without exceeding specified temperature requirements.
Current Balance Relay
Relay that allows tripping whenever there is an abnormal change in the division of current between two circuits. Current Rating-See Rated Coil Current and Rated Contact Current.
A relay which is designed to operate at a particular rated coil current rather than at a given rated coil voltage.
A controlling mechanism, which opens or closes contacts according to a preset cycle.
Distance between the contact pieces of an open contact, as measured at the narrowest point.
According to the different switching functions of contacts different contact types are distinguished. Distinction is also made between single and double contacts. The contacts directly moved by the drive system are active contacts, not actuated contacts are passive contacts.
Test method for the reliability of contacts for switching dry circuit.
The shortest distance between two isolated bare live parts that must be isolated from each other.
The shortest distance along the surface of an insulating material placed between two bare live parts that must be insulated from each other.
Relays designed to operate with DC input.
Dependent time measuring relay
A measuring relay for which times depend, in a specified manner, on the value of the characteristic quantity.
To deenergize a relay is to disconnect the relay coil from its power source.
A readily available relay which has some electrical or mechanical feature, which distinguishes it from a general purpose relay. Types of definite purpose relays are interlock, selector, stepping, sequence, latch-in and time-delay.
A relay that is intentionally designed for a time delay between energizing or deenergizing instant and the time that the relay contacts open or close.
A relay having multiple windings which functions when voltage, current, or power difference between windings reaches a predetermined value.
A relay that allows tripping for current flow in one direction only.
The ability of a protective system to distinguish between power system conditions for which it is
intended to operate and those for which it is not intended to operate.
A combination in which a movable contact simultaneously makes and simultaneously breaks the connection between two stationary contacts is called double-break contacts and is abbreviated
A double-wound coil is a winding consisting of two parts wound on the same core.
The ratio of the limiting values of the characteristic quantity at which the relay resets and
operates. This value is sometimes called the differential of the relay
Drop-out or Drop-out Values
Drop-out current, voltage, or power is the maximum value for which contacts of a previously energised relay will always assume their unenergised positions.
The dropout current is the maximum current at the relay coil, when the relay falls back into the rest position.
Maximum voltage at the relay coil, when the relay falls back into the rest position.
For normally open contacts: The time from switching off the coil excitation to the opening of the contact.
For normally closed contacts: The time from switching off the excitation coil until the moment of contact. (no bounce)
For change-over contacts: The time from switching off the coil excitation to the first contact with the opposite contact.
Rated working time of a device compared to its idle time.
A set of contacts that have two contacting positions, each of which closes a different circuit. Contact sets consisting of only one contacting position for closing the circuit are called single throw contacts.
Double or Reinforced Insulation
Insulation, which consists of base insulation and additional insulation.
Power consumption of the coil in watts.
Diffusion alloy contacts
Contacts made using diffusion processing.
The maximum value before insulation damage occurs when voltage is applied for one minute to an isolated metallic part (especially charged metal). The voltage is applied at the same location as the insulation resistance.
The leakage current (the current used to detect insulation damage) is normally 1 mA.
Sometimes, however, leakage currents of 3 mA and 10 mA are used.
Earth fault protective system
A protective system which is designed to respond only to faults to earth.
A three-phase transformer intended essentially to provide a neutral point to a power system for
the purpose of earthing.
The range of values of the characteristic quantity or quantities, or of the energizing quantities to
which the relay will respond and satisfy the requirements concerning it, in particular those
The ‘setting’ of a protective system including the effects of current transformers. The effective
setting can be ex-pressed in terms of primary current or secondary current from the current
transformers and is so designated as appropriate.
A device designed to produce sudden predetermined changes in one or more electrical circuits
after the appearance of certain conditions in the electrical circuit or current controlling it.
NOTE: The term ‘relay’ includes all the ancillary equipment calibrated with the device.
An electrical relay in which the designed response is developed by the relative movement of
mechanical elements under the action of a current in the input circuit.
A qualify term applied to a relay indicating that following an operation its contacts must be reset electrically to their original positions.
A relay whose operation involves use of a magnetic field, which is produced by an electromagnet.
Electrostatic Spring Shields
Metallic shields between two relay springs to minimize capacitance between them.
A relay, which has both coil and contacts, protected from the surrounding medium by a cover that is not airtight.
To energize a relay is to apply rated voltage to its coil. Extension Spring-Same as Restoring Spring.
The electrical quantity, either current or voltage, which alone or in combination with other
energizing quantities must be applied to the relay to cause it to function.
Admissible number of operations with a survival probability of 95% for a given contact load under specified conditions (max. switching frequency, max. contact resistance, response or drop values, insulation values, etc.).
The durability of contacts when a rated load is applied and the contact is switched at a specified switching frequency.
A high-speed relay specifically designed for short operating time but not short release time.
Fast-operate, Fast-release Relay
A high-speed relay specifically designed for both short operate time and short release time.
Fast-operate, Slow-release Relay
A relay specifically designed for short release time but not short operate time.
A high-speed relay specifically designed for short release time but not short operate time.
Stationary contacts of a relay which are engaged and disengaged by moving contacts to make or break circuits.
Sometimes used for Transfer Time.
The percentage of failures per unit time during continuous relay switching (number of operations) under individually specified test types and loads. The failure rate will change depending on the switching frequency, the environmental conditions, and the expected reliability level. Failure rates must always be checked on equipment under real operating conditions.
The magnetic characteristics caused by the shape around directly opposing magnetic surfaces.
A collective term for all operations of foreign-layer destruction in a closed, static electrical contact.
Contacts, which have contact, follow.
The structure on which the coil and contact assembly are mounted.
Sometimes used for the stationary contact of single-pole normally open contacts. (See also Contact Nomenclature).
Same as Normally Open Contacts.
The largest current in the relay coil, in which no actuation of the contacts takes place.
Fire Safety Specifications
An assessment of the resistance against fire and possibly continued burning independently.
Flexure is a type of drive method for the contact spring. With flexuretype relays, the contacting force is obtained from a stud, card, or other pushing force.
The problem where discharge between opposing conductors causes a short-circuit.
This often occurs with contacts used with medium and large currents.
An airtight relay, the sealing of which involves the use of a gasket, which is not bonded to the other sealing material.
A readily available relay, which has design, construction, operational characteristics, and ratings such that it is adaptable to a wide variety of uses.
Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted. Energy or information can still be exchanged between the sections by other means, such as capacitance, induction or electromagnetic waves, or by optical, acoustic or mechanical means.
Galvanic isolation is used where two or more electric circuits must communicate, but their grounds may be at different potentials. It is an effective method of breaking ground loops by preventing unwanted current from flowing between two units sharing a ground conductor.
Is a non-covering gold layer (layer thickness smaller 0.5μm) and serves as a so-called bearing protection. Because of being a porous gold layer the protective effect is controversial. Switching-wise the gold flash is irrelevant.
Contacting surfaces cannot open easily, even though they are not fused together or mechanically caught.
Note: Gluing occurs easily for contact surfaces of a low hardness that are clean.
A qualifying term applied to a relay indicating that following an operation the contacts must be reset manually to their original positions.
The part of a hermetically sealed relay through which electrical terminals pass.
Hermetically Sealed Relay
An airtight relay the sealing of which involves fusing or soldering but does not use a gasket.
A relay specifically designed for short operates time, release time, or both.
The hold current, voltage, or power is the minimum value for which contacts of a previously energised relay will always maintain their energised positions.
Homing is a qualifying term applied to a stepping relay indicating that wipers, upon completion of an operational cycle, are stepped around or back to the start position.
Hum, as applied to relays, is the sound caused by mechanical vibration resulting from alternating current flowing in the coil.
Hard gold plating
Is a covering gold layer applied to the base contact material. It prevents contact corrosion and is used for switching small loads (dry circuits) where no or only very small arcs arise.
This classification refers to the structure of the electromagnet. Hinged relays directly or indirectly switch contacts by the rotating movement of the armature around the fulcrum.
The status where power is supplied to contacts and the power that has been supplied to the coil is turned OFF then ON. Also the mustoperate voltage at that time.
Coils, which have been permeated with phenolic or similar varnish to protect them from mechanical vibration, handling, fungus, and moisture.
Independent time measuring relay
A measuring relay, the specified time for which can be considered as being independent, within
specified limits, of the value of the characteristic quantity.
An inductive winding, as contrasted with a noninductive winding, as a coil having an inductance.
A relay which operates and resets with no intentional time delay.
NOTE: All relays require some time to operate; it is possible, within the above definition, to discuss the operating time characteristics of an instantaneous relay.
A relay composed of two or more coils with their armatures and associated contacts so arranged that freedom of one armature to move or its coil to be energised is dependent upon position of the armature.
A relay, which must be deenergised at occasional or periodic intervals to avoid excessive temperature.
Inverse time delay relay
A dependent time delay relay having an operating time which is an inverse function of the
electrical characteristic quantity.
For inductive loads, an indication of the life expectancy is different from application to application, because of increased inrush currents and the voltage spike when turning off. The different load types are summarized in several application categories, they correspond to the switching behavior of motors or transformers, for example.
Inrush Current (making capacity)
The highest current at the moment of switching on. Pay special attention to capacitors, when heating coils or lamps are within the circuit, especially since the inrush current can be substantially higher than the operating current. It can then amount to more than 10 times the value of the breaking current.
Is the minimum resistance value at from each other isolated parts measured with an ohm meter or galvanometer at 500V DC. If the contacts are much better insulated against the coil or ground, this is noted accordingly in the relays table.
Information on existing insulation between conductive parts.
Sudden loss of insulation due to the voltage applied to two electrodes either side of the insulating material.
The resistance of the isolated sections between contacts and coils, conducting terminals and uncharged metallic parts (e.g., core frame and core), or between contacts.
This value is given for the relay and does not include lands on PCBs.
1. Between coils and contacts: Between coil terminals and all contact terminals
2. Between contacts with different polarity: Between contact terminals of different polarity
3. Between contacts with the same polarity: Between contact terminals with the same polarity
4. Between set coils and reset coils: Between set coil terminals and reset coil terminals
Impulse withstand voltage
The maximum abnormal voltage that the relay can withstand when the voltage surges momentarily due to lightning, switching an inductive load, etc. The surge waveform, unless otherwise specified, is the standard impulse voltage waveform according to JIS C5442, i.e., 1.2 × 50 µs.
Contacts made of two different metals pasted together.
Dry circuits U < 80mV, I < 10mA
Low level circuits U < 300mV, I < 10mA
Minimum current circuits (in which "short arcs" occur)
Intermediate level circuits (loads in the intermediate region) U < 12 V, I < 300 mA
High level circuits (in which stable arcs are characteristic) U > 12V, I > 300mA
MBB (Make Before Break) contacts (Shorting contacts)
MBB contacts are part of the group of contacts that have a specified operating sequence. MBB contacts are a set of contacts in which the contacts that should close at operation close before opening the contacts that need to open. Double-throw contacts so arranged that moving contact establish a new circuit before disrupting the old one
The protective system which is normally expected to operate in response to a
fault in the protected zone.
Same as Front Contact.
Magnetic Air Gap
A magnetic air gap is a nonmagnetic portion of a magnetic circuit.
The sticking of a relay armature to the core, after de-energization, due to residual magnetism of the core.
Sometimes used for Relay.
Maximum contact voltage
The maximum contact voltage that can be switched. Never exceed this value during operation.
Maximum contact current
The maximum contact current that can be switched. Never exceed this value during operation.
The minimum voltage required to operate the relay (JIS C5442). The value is given for a coil temperature of 23°C.
The maximum voltage that the relay for which the relay will release when the voltage drops dramatically or gradually decreases (JIS C5442).The value is given for a coil temperature of 23°C.
Minimum pulse width
For latching relays, the minimum pulse width of the rated voltage applied to coils to set and reset the contacts. The value is the rated voltage applied to the coil at an ambient temperature of 23°C.
Sometimes used for operate Time.
A relay, which functions in response to, predetermined changes in the value of coil current or voltage.
An electrical relay intended to switch when its characteristic quantity, under specified
conditions and with a specified accuracy attains its operating value.
A relay, which is actuated by rotation of the shaft of some type of motor, for example, a shaded-pole, induction-disk, or hysteresis motor.
A contact which, when the relay is energized or de-energized, is mechanically displaced to engage or disengage one or more stationary contacts.
Contacts so arranged that, when they open, the circuit be interrupted in two or more places.
Maximum switching capacity
The maximum load capacity that can be switched. Design circuits to ensure that this value is not exceeded during operation. Maximum switching capacity is expressed as VA for AC relays and W for DC relays.
Contacts with a multi-layer construction, using plating, joining, or other method.
The durability of contacts when no load is applied and the contact is switched at a specified switching frequency.
A neutral relay, in contrast to a polarised relay, is a relay in which the movement of the armature is independent of direction of flow of current through the relay coil.
A term used to describe a contact transfer in which the movable contact leaves one contact before touching the next.
A qualifying term applied to a stepping relay indicating that wipers, upon completion of an operational cycle, do not return to the home position, but are at rest on the last used set of contacts.
A type of winding in which the magnetic fields produced by two parts of the winding cancel each other and provide a non - inductive resistance.
A non-magnetic material attached to the armature or core of a relay to prevent iron-to-iron contact in an energised relay.
The non-operate voltage, current, or power is the maximum value for which contacts of a previously deenergised relay will always maintain their deenergised positions.
Deenergised position, open or closed, of contacts due to spring tension or gravity.
Normal Sequence of Operation
The sequence in which all normally closed contacts open before closure of normally open contacts of the assembly.
A relay in which no attempt has been made either to increase or decrease the operate time or the release time.
Normally Closed Contacts
A combination of a stationary contact and movable contact, which are engaged when the coil is deenergised.
Normally Open Contacts
A combination of a stationary contact and a movable contact which are not engaged when the coil is deenergised.
A relay which switches in response to a specific number of applied impulses.
Number of contact poles
The number of contact poles is referred to as the number of contact circuits.
Contacts on a stepping relay used to indicated when the wiper has reached the limiting position on its arc and must be returned to normal before the circuit can function again.
Stationary contacts on a homing stepping relay used to indicate when the wiper is not in the starting position..
If a relay has only normally closed contacts, its operate time is the longest time interval given by definition (a) below. If a relay has normally open contacts (regardless of whether or not it has normally closed contacts) its operate time is the longest time interval given by definition (b).
(a) Operate Time for Normally Closed Contacts: operate time for normally closed contacts is total elapsed time from the instant the coil is energised until contacts have opened; i.e., contact current is zero.
(b) Operate Time for Normally Open Contacts: operate time for normally open contacts is total elapsed time from the instant the coil is energised until contacts are closed and all contact bounce has ceased
Operating time characteristic.
The curve depicting the relationship between different values of the characteristic quantity
applied to a relay and the corresponding values of operating time.
The force that operates on a contact to open it.
The operating speed when a closed contact opens.
Voltage, Current, or Power is the minimum value for which contacts of a previously deenergised relay will always assume their energised position.
The rated AC frequency of the supply voltage at which the relay coil is designed to operated.
A relay, which is specifically designed to operate when its coil current reaches a predetermined value above normal.
The overshoot time is the difference between the operating time of the relay at a specified value
of the input energising quantity and the maximum duration of the value of input energising
quantity which, when suddenly reduced to a specific value below the operating level, is
insufficient to cause operation.
Over Voltage Relay
A relay, which is specifically designed to operate when its coil voltage reaches a predetermined value above normal.
The temperature of the relay during operation, after reaching the thermal equilibrium.
Is the voltage at which a relay is operated. The excitation voltage range indicates the range in which the operating voltage must be so that the relay is working correctly.
Contacts that are available to the customer for switching a load.
Contacts on the relay for free use.
The Operate Time of a relay is the transition time from the moment when voltage is applied to the relay coil to the moment the normally open switch contact(s) close. The Operate Time of a relay includes the time for the coil to build up the magnetic field (magnetic attraction is necessary to attract and close the contact), the transfer time of the moveable contact (from its open to its close position), and the bounce time after the closing of the switch (relays can bounce up and down a number of times before finally settling permanently in its close position).
Operating bounce time
The bounce time for NO contacts when the coil rated voltage is applied at a coil temperature of 23°C.
Partially Enclosed Relay
A relay which has either contacts or coil (but not both) protected from the surrounding medium by a cover that is not airtight.
Partially Sealed Relay
A relay which has either contacts or coil (but not both) sealed.
A relay is said to ‘pick-up’ when it changes from the un-energized position to the energized
Pick-up voltage, current, or power is the minimum value for which contacts of a previously deenergised relay will always assume their energised position.
A set of contact arms, assemblies, or springs placed one on top of the other with insulation between them.
A means of interconnection between relaying points for the purpose of protection.
A relay which is dependent upon the polarity of the energizing current to operate.
The pole face is the part of the magnetic structure on the end of the core nearest the armature.
The apparatus, including protective relays, transformers and ancillary equipment, for use in a protective system.
A relay designed to initiate disconnection of a part of an electrical installation or to operate a warning signal, in the case of a fault or other abnormal condition in the installation. A protective relay may include more than one unit electrical relay and accessories (for more details please see Relay Tutorial)
The coordinated arrangements for the protection of one or more elements of a power system. A protective scheme may comprise several protective systems Protective system.- A combination of protective gear designed to secure, under predetermined conditions, usually abnormal, the disconnection of an element of a power system, or to give an alarm signal, or both.
The portion of a power system protected by a given protective system or a part of that protective system.
Same as Pick-up Values.
Sometimes used for Pick-up Values.
Current which a relay contact can carry continuously under specified conditions without exceeding the permitted warming.
This classification refers to the structure of the electromagnet. The armature in a plunger relay is at the center of the coil and it moves along the coil axis.
Contacts with plating on the contacting surface.
a characteristic curve having a piecewise-linear shape and corresponding to the conversion by a device (or system) of a continuous input variable x into discrete values yn of an output variable y, where n is the number of possible values or levels of the output variable; usually n is equal to 2 or 3. Thus, the curve characterizes the operation of a relay.
The time from the moment the rated voltage is removed from the coil until the contact releases. For relays with more than one contact, the release time is the time until the slowest contact releases, unless otherwise defined (JIS C5442).
For relays with only NO contacts, the release time is the time until the slowest NO contact opens. The release time is given for a coil temperature of 23°C and does not include bounce time.
Reset time (for latching relays only)
The time from when the rated voltage is applied to the reset coil until the contact releases. For relays with NO contacts only, it is the time until the slowest NO contact opens.
For relays with more than one contact, the reset time is the time until the slowest contact releases, unless otherwise specified.
Release bounce time
The bounce time for NC contacts when the coil rated voltage is removed at a coil temperature of 23°C.
A stepping relay actuated by an armature-driven ratchet.
Rated Coil Current
Steady-state coil current at which the relay is designed to operate.
Rated Coil Voltage
Coil voltage at which the relay is designed to operate.
Rated Contact Current
Current, which the contacts are designed to carry for their rated life.
A standard value for stipulating contact performance, expressed as a combination of contact voltage and contact current.
Rated power consumption
The power consumed by the coil when rated voltage is applied to the coil (rated voltage × rated current). The rated power consumption for AC specifications is the value at a 50-Hz frequency.
The nominal value of an energising quantity which appears in the designation of a relay. The
nominal value usually corresponds to the CT and VT secondary ratings.
Ratio, expressed in percent, of drop-out current to rated current or the analogous voltage ratio.
If a relay has only normally open contacts, its release time is the longest time interval given by definition (a) below. If a relay has normally closed contacts (regardless of whether or not it has normally open contacts) its operate time is the longest time interval given by definition (b).
(a) Release Time for Normally Open Contacts: release time for normally open contacts is total elapsed time from the instant the coil current starts to drop from its rated value until contacts have opened, i.e., contact current is zero.
(b) Release Time for Normally closed Contacts: release time for normally closed contacts is total time from the instant the coil current starts to drop from its rated value until contacts are closed and all contact bounce has ceased.
Release current, voltage, or power is the maximum value for which contacts of a previously energised relay will always assume their unenergised positions.
A timing device, which upon completion of one operating cycle continues to repeat automatically until excitation is removed.
The limiting value of the characteristic quantity at which the relay returns to its initial position.
The algebraic sum, in a multi-phase system, of all the line currents.
The algebraic sum, in a multi-phase system, of all the line-to-earth voltages.
Length of the magnetic air gap between the pole-face center and nearest point on the armature when the armature is in the energised position.
Residual Pins or Screws
Nonmagnetic pins or screws attached to either the armature or core of a relay to prevent the armature from directly contacting the magnetic core.
Value of the residual gap obtained by the use of an adjustable residual screw.
A spring, which moves the armature to and holds it in the normal position when the relay is deenergised.
Sometimes used for Restoring Spring.
Sometimes used for Motor-driven Relay.
Rotary Stepping Relay
Same as Stepping Relay.
Rotary Stepping Switch
Same as Stepping Relay.
Relays with polarity
DC relays that change status depending on the polarity of the control input current.
Note: There are single-side stable relays, double-sided stable relays, and centrally stable relays.
Relays that are not affected by the polarity of the control input current are called nonpolarized
relays (neutral relays).
The response delay is a time that elapses from creating a response voltage until the actual response. Response delay, release delay, transient pulses, blinking mode and pulse shaping are often achieved by electronic timing elements that are connected upstream of the relay. Either the functions are combined with the relay in a component (time relay) or with the relay in a socket as a module.
For normally open contacts: The time from switching the coil to the first contact.
For normally closed contacts: The time from switching the coil until the contact is opened.
For change-over contacts: The time from switching the coil to the first contact with the contact to be closed.
Minimum value of the excitation voltage, which brings a relay to operate. The specification of response voltage is usually based on 20°C.
A relay, which has both, coil and contacts enclosed in an airtight cover.
Sometimes used for Wiping Contacts.
A relay capable or automatically selecting one or more circuits from a number of circuits.
The limiting value of a ‘characteristic’ or ‘energising’ quantity at which the relay is designed to operate under specified conditions. Such values are usually marked on the relay and may be expressed as direct values, percentages of rated values, or multiples.
Automatic control of a series of operations in a predetermined order.
A relay, which controls two or more sets of contacts in a definite, predetermined sequence.
Sometimes used for Shading Ring.
A shorted turn surrounding a portion of the pole of an alternating current magnet, causing a delay of change of magnetic flux in that part, thereby preventing contact chatter.
Sometimes used for Auxiliary Relay.
Slow-operate, Fast-release Relay
Relays specifically designed for long operate time and short release time.
A slow-speed relay which has been specifically designed for long operate time but not for long release time.
Slow-operate, Slow-release Relay
A slow-speed relay specifically designed for both long operate time and long release time.
A slow-speed relay specifically designed for long release time, but not for long operate time.
Relays specifically designed for long operate time, release time, or both.
A highly conductive sleeve placed over the core to aid in retarding the establishing or decay of Flux within the magnetic path.
Sometimes used for a Plunger Relay.
A relay, which has an application, that requires special features, which are not characteristic of conventional general purpose or definite-purpose relays.
Specified duty Relay
A relay which is designed to function with a specified duty cycle but which might not be suitable for other duty cycles.
A bearing member made of insulating material, which transmits motion of the armature to the movable contact and from one movable contact to another in the same pile-up. Spring Pile-up.-Same as Pileup.
Same as Spring Buffer.
The quality whereby a protective system remains inoperative under all conditions other than
those for which it is specifically designed to operate.
The r.m.s. value of the symmetrical component of the through fault current up to which the
protective system remains stable.
A unit relay which responds to abnormal conditions and initiates the operation of other elements of the protective system.
Is an electrical relay in which the response is developed by electronic/magnetic/optical or other components, without mechanical motion of components. (for more details please see the Relay Tutorial)
The term ‘static relay’ is generally referred to a relay incorporating solid state components like transistors, diodes, resistors, capacitors, etc. In this type of relay, the functions of comparison and measurement are performed by static circuits wherein there are no moving parts. (for more details please see the Relay Tutorial)
A contact member which is rigidly fastened to the relay frame and which is not moved as a direct result of energizing or deenergizing the relay.
A relay whose contacts are stepped to successive positions as the coil is energised in pulses. Some stepping relays may be stepped in either direction. (The Stepping Relay is also called a Rotary Stepping Switch or a Rotary Stepping Relay.)
System impedance ratio (S.I. R.)
The ratio of the power system source impedance to the impedance of the protected zone.
Temperature increase of a device during operation due to the power loss occurring in the device, eg the coil and the contacts of the relay.
In monostable relays it means that the anchor does not return to the rest position after the excitation of the coil. The reason for this may be either too low return force or high remanence in the iron circuit. This effect can be counteracted by applying a release sheet or release pin.
Removing the difference due to the effect of magnetic history by applying a saturation current to the operating coil during measurement of operation or release voltage (or current) or during testing.
Note: The current used is called the soak current.
The shock resistance of a relay is divided into two categories:
Destruction, which quantifies the characteristic change of, or damage to, the relay due to considerably large shocks which may develop during the transportation or mounting of the
Number of relay operations per unit time.
Set time (latching relays only)
The time from the moment when the rated voltage is applied to a set coil until the contact operates. For relays with more than one contact, the set time is the time until the slowest contact operates, unless otherwise defined (JIS C5442).
The set time is given for a coil temperature of 23°C and does not include bounce time.
Contacts created using powder metallurgy.
Sometimes used for Restoring Spring.
A relay, which is operated by the heating effect caused by electric current flow.
Through fault current
The current flowing through a protected zone to a fault beyond that zone.
A delay intentionally introduced into the operation of a relay system.
Time-delay Relay or Time-lag Relay
A relay in which a delayed action in operation or resetting is purposely introduced.
A motor-driven or Electronically time-delay relay.
Transfer Time or Transit Time
Total elapsed time between breaking one set of contacts and making of another set of contacts.
(a) Transfer Time on Operate Transfer time on operate is total elapsed time from the instant the normally closed contacts start to open until the normally open contacts are closed and all contact bounce has ceased.
(b) Transfer Time on Release Transfer time on release is total elapsed time from the instant the normally open contacts start to open until the normally closed contacts are closed and all contact bounce has ceased.
Trip voltage, current, or power is rated value at which a bistable-polarised relay will transfer from one contact to another.
Contacting surfaces and surrounds are affected by electrical discharge or Joule heat and part of the material from one contact transfers to the other opposing contact.
Under current Relay
A relay specifically designed to function when its coil current falls below a predetermined value.
Under voltage Relay
A relay specifically designed to function when its coil voltage falls below a predetermined value.
A relay, which does not have its contacts or coil, protected from the surrounding medium by a cover.
Unit electrical relay
A single relay, which can be used alone or in combinations with others.
A protection system, which is designed to operate only for abnormal conditions within a clearly defined zone of the power system.
A protection system which has no clearly defined zone of operation and which achieves selective
operation only by time grading.
The vibration resistance of a relay is divided into two categories:
Destruction, which quantifies the characteristic changes of, or damage to, the relay due to considerably large vibrations which may develop during the transportation or mounting of the relay, and malfunction durability, which quantifies the malfunction of the relay due to vibrations while it is in operation.
relay, and malfunction durability, which quantifies the malfunction of the relay while it is in operation.
A magnetic or thermal winding to which energy is supplied to activate the relay.
A moving contact on a stepping relay.
Contacts designed to have some relative motion during the interval from the instant of touching until completion of the closing motion.
The sliding action performed after two opposing contacts make contact.
This wiping action helps to reduce the impact of film or dust that collects on the surface of contacts.
Contacting surface and surrounds fuse together and are difficult to open.