alternating current


Self-consumption of the coil in Watt.

basic insulation

Insulation of live parts, for basic protection against dangerous body currents. (VDE 0110-1:1997, section

bathtub curve

Course of the failure rate l as a function of the main influencing factor (e.g. time, switching cycles, etc.). This process can generally be divided into three main areas.

  • Early failures: Here the failure rate has a decreasing tendency.
  • Random failures : In this range the failure rate is constant; this range is called "service life".
  • Wear-out failure: There the failure rate increases due to wear and tear.

Alternative terms: burn-up, combustion loss

The burn-off is a loss of material at the contacts caused by switching arcs.


Conductive part (relay contact) intended to connect or disconnect electrical circuits.

Contact arrangement
Alternative terms: Contact configuration

Combination of different contact types.

contact force

force which two contact members exert against each other at their contact points in the closed position

Contact material

Contact materials can be fine grain silver (AgNi0,15), hard silver (AgCuNi, AgCu3), silver cadmium oxide (AgCdO10), silver tin dioxide (AgSnO~2~ 10P), tungsten (W), hard gold (Au...) or silver nickel 10 (AgNi10). The contact material used has a significant influence on the performance of the relay.

The contact loads should always be connected in order to avoid or reduce current peaks when switching on and voltage peaks when switching off. Such a measure reduces the wear of the contact pieces and thus increases the service life. This applies in particular to material migration. (contact load capacity)

Contact spacing
Alternative terms: contact gap, contact distance

Distance between the contact pieces of an open contact, measured at the narrowest point.

Contact spring

Elastic part of a contact. Usually carries at least one contact piece. (Electromechanical relay)

Contact types

Different contact types are distinguished according to the different switching functions of the contacts. In addition, a distinction is made between single and double contacts. The contacts directly moved by the drive system in the contact set are active contacts, the contacts not actuated are passive contacts.

continuous current

Current that a relay contact can carry continuously under specified conditions without exceeding the permissible temperature rise.

Cycling Test

Test method for the reliability of dry switching contacts.


direct current

Double or reinforced insulation

Insulation consisting of basic insulation and additional insulation.

drop current

The drop current is the maximum current in the relay coil at which the relay drops back to its rest position.

dropout time
Alternative terms: fallback time

For working contacts: The time from switching off the coil excitation until the contact is opened.
For normally closed contacts: The time from when the coil excitation is switched off until the contact is made. (without bounce time)
For changeover contacts: The time from switching off the coil excitation until the first contact is made with the opposite contact.

dropout voltage

Maximum voltage at the relay coil at which the relay drops back to its rest position.

Electrical life

Permissible number of operations with a survival probability of 95% at a given contact load under specified conditions (max. switching frequency, max. contact resistance, response or waste values, insulation values, etc.).

Fault current
Alternative terms: residual current

Largest current in the relay winding at which the contacts have not yet been actuated.

Fire protection requirements

The resistance to inflammation and possibly independent continued burning is assessed.


A collective term for all processes of foreign layer destruction in the closed, stationary electrical contact.

Galvanic isolation

Safe, potential-free insulation between conductive parts.

Gold flash

Is a non-covering gold layer (layer thickness less than 0.5µm) and serves as so-called bearing protection. However, this protective effect is controversial due to the porous gold layer. The gold plating is not relevant for the switching technology.

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 are generated.

Inductive load

In the case of inductive loads, the service life specifications vary from application to application due to the increased inrush currents and the voltage peak at switch-off. The different types of loads are grouped into several categories of use, which correspond, for example, to the switching behaviour of motors or transformers.

Inrush current
Alternative terms: making capacity

The highest current at the moment of switching on. It must be taken into particular consideration when capacitors, heating coils or lamps are in the circuit, especially as it can then be considerably higher than the operating current. It can then be more than 10 times the value of the breaking current.

Insulation resistance

Is the smallest resistance value measured on parts isolated from each other with an ohmmeter or galvanometer at 500V DC voltage. If the contacts are much better insulated against the coil or ground, this is noted accordingly in the relay table.

Insulation values

Information on the existing insulation between conductive parts.

load ranges
  • Dry circuits U < 80mV, I < 10mA
  • Low level circuits U < 300mV, I < 10mA
  • Minimum current circuits (low load circuits in which "short arcs" occur)
  • Intermediate level circuits U < 12 V, I < 300 mA
  • High level circuits (heavy load circuits in which stable arcs are characteristic) U > 12V , I > 300mA
  • Low power contacts (power contacts for low switching capacity).
  • Power contacts (power contacts)

mounting position

Indicates the required position of the relay to ensure proper relay operation. All ELESTA GmbH relays can be installed as required. There is no prescribed mounting position.

normally closed
Alternative terms: break contact, NC, opener

contact which is open when the relay is in its operate condition and which is closed when the relay is in its release condition

normally open
Alternative terms: make contact, NO, NO contact

Relay contact that is closed in the working position of the relay and open in the rest position.

Operating temperature

The temperature of the relay when it reaches thermal equilibrium during operation of a relay.

operating voltage

The voltage at which a relay is operated. The excitation voltage range indicates the range in which the operating voltage may lie, so that the relay still functions correctly.

output contacts

Contacts available to the customer for switching a load.

output side

Contacts on relay for free use.

response delay

The response delay is a time that elapses between the application of a response voltage and the actual response. Response delay, release delay, wipe pulses, flashing and pulse shaping are often achieved by electronic timers connected upstream of the relay. Either the functions can be combined with the relay in one module (time relay) or as a module with the relay in one socket.

response time

For normally open contacts: The time from switching on the coil until the first contact is made.
For normally closed contacts: The time from switching on the coil until the contact opens.
For change-over contacts: The time from switching on the coil until the first contact is made with the contact to be closed.

response voltage

Smallest value of the excitation voltage that causes a relay to respond. The response voltage specification is normally related to 20°C.


Temperature increase of a device due to the power loss occurring in the device during operation, e.g. of the coil and the contacts of the relay.


In the case of monostable relays, this means that the armature does not return to its rest position after coil excitation. This can be caused either by too little restoring force or too high remanence in the iron circuit. This effect can be counteracted by attaching a separating plate or pin.

utilization category

The utilization category is defined for electrical switchgear or fuses. It is defined as the "combination of specified requirements selected taking into account the operating conditions of a switchgear or fuse to meet a significant group of practical applications". The specified requirements may include, for example, making capacity (if applicable), breaking capacity and other parameters such as the short-circuit rating, the data of the associated circuits, the corresponding conditions for operating behaviour and function.