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Here you will find terminology definitions and technical details designed to make it easier for you to fulfil your tasks in the management of switching system projects.


Auxiliary switch

A switch that has one or more control and/or auxiliary contacts and is mechanically operated by a switching device.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1


Breaking capacity
(of a switching device or fuse)

Prospective current that can switch off a switching device or fuse at a defined voltage under specified conditions.
The voltage and the specified conditions are set out in the respective device norms.
DIN EN 60947-1
(VDE 0660-100) EN 60947-1


Cam switches

Cam switches are manually operated switching devices that are primarily used as motor switches, load switches, breakers, on-load tap changers and auxiliary switches (control switches) in main and auxiliary circuits of low-voltage equipment.
Classic cam switches are constructed on a modular principle. Contact chambers, also called contact elements or lines, are lined up next to each other in rows based on the requirements of a contact diagram. 1, 2 or 3 double breaking contacts per contact chamber are possible. Cam wheels that sit on a common axle penetrating through the pack of switches steer the moving connection terminals into the contact chambers. That these connection terminals end up in the desired position is ensured by them snapping into place. The snap-lock ratchet is housed in the snap-lock chamber and fitted upstream of the contact chambers.

Category of use

A combination of defined requirements that have been selected bearing in mind the operating conditions of a switching device or fuse in order to correspond to a material group of practical cases of use.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Circuit breakers

Mechanical switching devices that can switch, guide and switch off currents under normal conditions within the electric circuit, inclusive of a specified overload during normal operation. In opened state the contacts fulfil the specifications of an isolator.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Circuit diagrams

In the case of cam and main switches all contacts are always depicted merely as closing contacts. Whether a contact in a special switch position is open or closed is shown as a cross in the matrix beneath the contacts. This type of drawing facilitates, especially in the case of cam switches with many switching stages, a much simpler and more transparent representation of the function.

Closer, ‘a’ contact

Control or auxiliary contact that is closed when the mechanical switching device’s main contacts are closed and open when they are open.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Compact switch

‘Compact switch’ is a term commonly used in the industry to describe a design of circuit breaker. Such switches are on/off or changeover switches designed for fitting in switching cabinets. The switches are mainly made for top hat rail mounting, floor or door installation. The screws attaching the switch are always accessible from one direction and lie in the direction of the cable run. However, the term is not defined in any standard. Elektra Tailfingen regards the DK1 to D7 and S1 to S7N ranges as compact switches.

Contact rating

The contact rating indicates how great the electrical load is permitted to be. The design and the type of the electronic load determine the contact rating.

Control devices

Control devices or operating elements are mechanisms that are used to operate machines.
Control devices can be electronically or electrically configured, for example as switches or buttons.

Conversion factors for current carrying capacity

Conversion factors for the current carrying capacity of PVC-insulated lines and cables at ambient temperatures other than 25° C

Creep switching

Contact where the switching movement arises from the activation speed.

Cut off (cut-off function)

Function to switch off the power supply of the entire plant or a part thereof, disconnecting for safety reasons the plant or relevant part from any electrical energy source.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1


Device plugs

They serve to supply current to electrical consumer units. Power is fed via an extension cable with a coupler. Different designs are possible as wall or surface-mounted connector plugs optionally with terminal strip and/or integrated phase inverter. ELEKTRA connector plugs are internationally standardised to VDE 0623 and IEC/ EN 60309.

Door coupling/locking

Possible in the case of ELEKTRA cam switches and ELEKTRA circuit breakers fixed to the floor. The control unit with the coupling drive is located here in the switching cabinet doors. The coupling with possible centring adjuster is located on the control spindle. The doors / casing covers can thus only be opened in switched off state. Thanks to our robust steel axis no support bars are generally needed even with large gaps.



The ability of a device “to work satisfactorily within its electromagnetic environment without introducing unacceptable interference into the environment or other devices” (IEC definition) is called Electro-Magnetic Compatibility.

In the case of devices within the range of applications of IEC/EN 60947-3, which do not contain any electronic circuits, such as circuit breakers or cam switches, electromagnetic interference can arise only during occasional switching processes, which take place within milliseconds. It is therefore taken as read that the requirements in relation to the emission of electromagnetic interference are fulfilled. Consequently no tests are necessary. Under normal operating conditions they are also not susceptible to any electromagnetic interference. Consequently no interference resistance tests are necessary.

The situation is different if the switch is part of a system and, for example, sits as a repair or maintenance system upstream of a motor that is powered using a frequency converter. It is possible that interference may come from this frequency converter, which makes it necessary to shield the lines from the motor. The switch must then be integrated into the shielding. ELEKTRA Tailfingen offers a complete range here based on different casing series.


Forced opening
(of a mechanical switching device)

Opening movement that ensures, based on defined conditions, that all main contacts are in the open position whenever the control is in the position that corresponds to the switching device’s open position.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1


IP protection type

In relation to their suitability for different ambient conditions many devices, including electrical ones, are subdivided into corresponding types of protection, known as IP codes. According to DIN the abbreviation IP stands for International Protection. In the English-speaking world, however, it is used as Ingress Protection. These codes are recorded in DIN EN 60529 under the title ‘Protection Types Provided by Casing (IP codes)’.

Isolator features

Function to switch off the power supply of the entire plant or a part thereof, disconnecting for safety reasons the plant from any energy source. The indicator of the position of the main contacts must be unambiguous and effective. It must be possible to lock the isolation mechanism as defined in DIN EN 60 204-1 in the ‘Off’ (isolated) position. DIN EN 60 947-3 makes increased demands in terms of the rigidity of controls in order to prevent it being possible for the control, in the case of a welded switch, to be moved into the ‘Off’ position. DIN EN 60 947-1; 2.1.19


Line ampacity

Current-carrying capacity and protection in the event of overloading lines and cables for fixed laying at 25° C ambient temperature (supplement 1 to DIN VDE 0100 part 430)

Line and cable inlets

Casing cable inlets and averages for cable screw connections’ sealing areas.


Magnetic overload relay or overload release

Overload relay or release, the activation of which is dependent on the force of an electromagnet, the coil of which gets excited by the current flowing in the main electric circuit.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Making capacity (of a switching device)

Is the value of the prospective inrush current that is able to activate the device under prescribed conditions at a specified voltage.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Motor protective circuit breaker

A switch that is used for switching and for protection. It protects the motor in the event of overloading, short-circuiting or failure of an external conductor. The motor coil gets protected through a thermal trip (overload protection) and an electromagnetic trip.

Motor rated current

One of the details on the motor’s type plate. When under load with nominal torque at rated speed and with connection to rated voltage, the rated current flows. For 3-phase alternating current that is the conductor current’s effective value.

Motor switches

Motor switches are used for direct control of motors. They may be on/off switches, reversing switches, single-phase starter switches, changeover switches, star-delta switches, pole-changing switches, on-load tap changers, multi-motor switches or group switches. ET offers a comprehensive range in all sorts of different designs, capacities and sizes.


Opener, ‘b’ contact

Control or auxiliary contact that is open when the mechanical switching device’s main contacts are closed and closed when they are open.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1


Operating conditions in an electrically fault-free circuit that cause an excess current.


Protection class

Protection classes are used in electrical engineering to categorise and identify electrical supplies (e.g. devices and installation components) in relation to the safety measures present designed to prevent electric shocks.

  • Protection class 0 / Basic insulation
  • Protection class I / Protective earthing
  • Protection class II / Protective insulation
  • Protection class III / Safety extra-low voltage

Symbols for identifying the protection class are defined in IEC 60417.
DIN EN 61140 (VDE 0140-1)
DIN VDE 0100-410 (VDE 0100-410)

Protection types

Depending on their intended purpose, our products need a certain type of protection. The protection type defines to what extent a product is protected from water or foreign bodies getting in. The letters IP (Ingress Protection as per IEC 60529) followed by two numbers are always used to designate the protection type. The first number (1-6) indicates the scope of the protection offered by the product’s housing in relation to foreign bodies. The second number (1-8) describes the protection against water. The higher the number, the greater the protection.

Protective insulation

Protective insulation is a protective measure. It provides protection from touching live electrical parts by laying an additional layer of insulation around the basic insulation required for normal operation. In this process metal casing can be additionally completely insulated on the inside or outside. The additional insulation must not be broken into anywhere, not even at a switch connection. The drawback is that the first fault is difficult / impossible to identify. Devices with protective insulation are permitted to have an unearthed connection cable and are marked by a symbol showing two squares, one inside the other. The protective insulation corresponds to protection class II.

Devices with protection class III have low-voltage electric circuits that are separated from mains electric circuits by protective insulation. This protective insulation is also used on isolating transformers. It is also known as safe electrical isolation.


Ratchet switching (using a foot switch as an example)

(progressive switching) Pedal is pressed and the contacts get closed and remain closed even after the pedal is released. Only when the pedal is pressed again do the contacts return to the starting position.

Rated operating voltage (Ue)

The rated operating voltage of a device is the voltage that, together with the rated operating current, determines how the device is used and on which the different tests and utilisation categories of use are based.

In the case of single-pole devices the rated operating voltage is generally the voltage across the pole.

For multi-pole devices it is generally specified as chained voltage.
DIN EN 60947-1
(VDE 0660-100) EN 60947-1

Rated operational current (Ie)

The rated operating current of a device is specified by the manufacturer and takes into account the rated operating voltage, the rated frequency, rated operating mode, the category of use and the type of casing, if any.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Rated uninterrupted current (Iu)

The rated uninterrupted current of a device is a current specified by the manufacturer that can run the device in continuous operation.
DIN EN 60947-1
(VDE 0660-100) EN 60947-1

Rated insulation voltage (Ui)

The rated insulation voltage of a device is the voltage on which insulation tests and creeping distances are based. The highest rated operating voltage may not under any circumstances be more than the rated insulation voltage.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Rated impulse withstand voltage (Uimp)

Peak level of an impulse voltage of defined form and polarity to which the device can be exposed without failing under prescribed test conditions and on which the air gaps are based.

The rated impulse withstand voltage of a device must be equal to or greater than the impulse surges (transient excess voltage levels) that arise in the system in which the device is being used.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

Repair and maintenance switch

Repair and maintenance switches are used to switch off machines and sections of plant machinery that are not directly linked to the control system or where there is a risk of them being inadvertently started up while maintenance or repair work is in progress. In order to make work safe for the workers it must be possible to lock these switches and they must have the same features as a main switch as defined by EN 60204.


Safety pedal switch

Over and above normal switching on, it also switches off in the event of danger if the pedal is switched beyond the pressure point. The switch locks in place and cannot be used again until it has been released.

Safety switches

Safety switches are enclosed main, repair or maintenance switches, the casing of which cannot be opened with the handle shut in the home position. ELEKTRA Tailfingen makes these with plastic, cast iron and steel plate casings.

Shunt release

An electromagnet that operates a release mechanism when voltage is applied. When no current is present the system is idle. Activation is by means of an ‘a’ contact.

Shunt releases are used as a means of remote release when a break in voltage is not to lead to automatic switching off. The release does not work if wires are broken, contact is faulty or voltage is low.

Snap-action switching

Regardless of the activation speed, the contact’s switching movement is performed with a snap-like action.

Switches with return action

In many technical applications it is necessary to operate machines and equipment in pulsed or inching mode only. In order to ensure that a device does not run continuously, ELEKTRA cam switches can be configured such that the after being operated the switch jumps back into its original position. Example applications for this include pneumatic platforms, where the switch has to be held in the up or down position until the desired position has been reached, or pumps, which normally only turn in one direction but for cleaning mode need to be briefly run ‘backwards’.

Switching angle

The so-called switching angle of a cam switch is determined by the ratchet and is generally 30°, 45°, 60° or 90°, meaning that when the switch handle has been turned by this number of degrees the switching process has been completed.

Switching capacity

Current that a switching device can turn on and off under set conditions.



Thermal overload relay or overload release

Delayed overload relay or release, the activation of which (including its delay) is dependent on the heating effect of the current flowing inside the relay or release trigger.

Thermally triggered overload protection

The thermally triggered protection works through bi-metals that get warmed up by heating coils (phase resistors), across which motor current flows. Its own bi-metal with associated heating coil is provided for each line carrying current to the motor. If the current absorbed by just one of the motor’s coils exceeds the prescribed level for several seconds, the bi-metal, deformed by the heat, releases the motor protection’s switching latch and breaks the electric circuit to the motor. Likewise, if an external conductor fails (bi-metal strips heated up unevenly) the motor gets switched off after a short delay (disjunction). After having thermally triggered, the switch cannot be switched on again until the bi-metals have cooled down. The trigger currents of thermally triggered motor protection switches can be adjusted within certain limits (up to a factor of 1.6) and must be set to the motor’s rated current. Attention must be paid here, particularly in the case of three-phase AC motors, to the coils’ type of switching (star or delta). After triggering, the protection cannot be reset until the bi-metal has adequately cooled down.

Touch switching
(using a pedal as an example)

Pedal gets pressed. Contacts remain closed for as long as the pedal is pushed. Once the foot is taken off the pedal, the contacts are open again.

Trip-free mechanism
(trip-free mechanical switching device)

Mechanical switching device, the moving contacts of which go back into the open position and stay there whenever the opening process (i.e. tripping) is initiated after the closing process has begun, including when the closing command remains in place.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1


Undervoltage relay or release

Relay or circuit breaker that permits the delayed or immediate opening or closing of a mechanical switching device when the voltage at the relay or breaker’s terminals drops below a prescribed level.
DIN EN 60947-1 (VDE 0660-100)
EN 60947-1

In the event of a power failure, the undervoltage trip coil causes the switch latch to activate and the switch releases. The drop-out voltage is between 35 and 70%, while the pull-in voltage is≥ 85% of the rated voltage.

Useful life

A differentiation is made between mechanical and electrical life. The number of no-load switching cycles, i.e. switched with no power, defines mechanical life, while on-load electrical life is specified as per the respective category of use. Electrical life is thus shorter than mechanical life.