Know How from A-Z

Know How from A - Z

On this page you will find definition of terms and technical data that will support you in your design work for electrical switchgear. The terms are in alphabetical order. If useful the comments are completed by technical tables. All technical information shown in our leaflets or catalogues are made with high diligence according to our long experience. Anyhow their use is without obligation. We assume no liability due to human error or misprint. Subject to alterations. Dimensions and weights are indicative only.


What are the Application / installation types?

Please see page 4.21-4.45 und 5.6/5.7 in our main catalogue

Front 4-hole mounting, Front 2-hole mounting, Front central mounting, Distribution board mounting, Base mounting, Rear mounting, Wall mounting, Wall mounting with plug (Plastic enclosures, Aluminium  cast enclosures)

What is an Auxiliary switch?

They serve as signal indicator or to control operations depending on the position of the switch device. They can be used for interlocking of other switches and for remote signalling of the switch position.

What are Cable glands metrical/PG?

Cable glands with PG threads in use until 2004 have been replaced completely in the enclosures made by
MERZ by the metrical thread version, normally used nowadays. Anyhow, in some of the purchased enclosures
the cable glands remain unchanged with PG threads. For a comparision table between metrical and PG threads.

Pg = Steel Conduit Thread


Pg 9 11 13,5 16 21 29 36 42 48
Orifice diam. in mm 15,5 19 21 23 29 37,5 47,5 54,5 60
Outside diameter of lines and cables from - to mm 4,5 - 7 6 - 9 9 - 12 11 - 14 14 - 18 18 - 25 25 - 32 30 - 38 34 - 42
M = metrical
M = metrical
M.. x 1,5 mm
12 16 20 25 32 40 50 63
Outside diameter
of lines and ables
from - to mm
3 - 6,5 5 - 10 6 - 12 11 - 16 15 - 20 19 - 27 26 - 34 32 - 44


What is an Cam switch?

Cam switches according to their contact arrangement are fitted with switching chambers with 1,2 or 3 (series 111 only) double interrupted conduct paths. Each conduct path is arranged of 2 firmly seated terminals and one mobile contact bridge which is guided by a plunger. The contact bridge is positively opened by the cam and closed by a spring. The indexing device is available in different torques and 4 different switching angles. The
finger proof cam switches are equipped with screws with captive plus-minus screw heads. All terminals are fitted with screwdriver guiding, funnel-shaped cable entries and in chamber like design. Cable end stops assure the correct insertion depth.

What is an Changeover switch?

Changeover switches are realized by the MERZ MN series and are either applicable to connect one source with two independent consumers or to connect two independent sources with one consumer. A typical representative of the second category is the „Net-0-Generator“ switch, which is at first disconnecting the main power supply in case of power breakdown safely from the internal net and then switching over to an independant external power generator. Changeover switches are available with up to 8 poles with or without 0-position.

What is an Code switch?

Are cam switches used as control switches and able to emit a binary coded switch diagram. These switches can generate at most a binary code from 0 to 11. An other type of binary code is the BCD code (using 0-9 for units/tens) which could be emulated as well by a cam switch.

What is an Compact Switches?

The term „compact switch“ is common practice in the industry and describes a switch design of disconnect switches. It is about On-Off switches or change-over switches arranged for switchboard installation. In the majority of cases the switches are drafted for snap-on DIN rail mounting, base mounting or front mounting in the door. The terminal screws are all accessible from one side and are situated in line of the conduct. The term is not defined by any normative. The series ML0 to ML3 are the compact switch series of MERZ.

What is an Contact diagram?

The contact diagrams within this catalogue are different to a DIN compatible diagram. All cam and main switch contacts are shown as normally open contacts only. Whether a contact in a certain switching position is open or closed is shown within the matrix by an X. This kind of diagram allows, especially with cam switches with lots of switching positions, a much more simple and transparent illustration of the switching functions.

What is an conventional enclosed thermal current Ithe?

Is the manufacturer defined current for temperature testing of the device, when the device is fitted into a specifed enclosure. IEC/EN 60947-1;

What is an conventional free air thermal current Ith?

The conventional free air thermal current ist the maximum testing current for temperature testing of devices in free air. The conventional free air thermal current must at least correspond to the maximum rated operational current of an open device during an eight hour operation. Free air is understood as air in common interior rooms almost free of airflow and radiation. IEC/EN 60947-1;

What is the Conversion factors for permissible current?

Conversion factors for permissible current loads of PVC-insulated lines and cables at ambient temperatures
other than 25°C.

Conversion factors for permissible current


Ambient temperature in °C 10 15 20 25 30 35 40 45 50 55 60
1,15 1,1 1,06 1 0,94 0,89 0,82 0,75 0,67 0,58 0,47


What is the Dodd-Frank Act?

The Dodd–Frank Wall Street Reform and Consumer Protection Act (commonly referred to as Dodd–Frank) is a United States federal law that was enacted on July 21, 2010. The law overhauled financial regulation in the aftermath of the Great Recession, and it made changes affecting all federal financial regulatory agencies and almost every part of the nation's financial services industry.

Dodd–Frank reorganized the financial regulatory system, eliminating the Office of Thrift Supervision, assigning new responsibilities to existing agencies like the Federal Deposit Insurance Corporation, and creating new agencies like the Consumer Financial Protection Bureau (CFPB). The CFPB was charged with protecting consumers against abuses related to credit cards, mortgages, and other financial products. The act also created the Financial Stability Oversight Council and the Office of Financial Research to identify threats to the financial stability of the United States, and gave the Federal Reserve new powers to regulate systemically important institutions. To handle the liquidation of large companies, the act created the Orderly Liquidation Authority. One provision, the Volcker Rule, restricts banks from making certain kinds of speculative investments. The act also repealed the exemption from regulation for security-based swaps, requiring credit-default swaps and other transactions to be cleared through either exchanges or clearinghouses.

What is the EMC - ElectroMagnetical environment?

EMC is defined as the ability of a device to work satisfactorily in it‘s electromagnetical environment without any unacceptable disturbances for this environment or other devices. (definition by IEC) Devices without electronic circuits as e.g. disconnect and cam switches can emit electromagnetic interferences during occasional switching operations only, which last for ms merely! As a result it is assumed that they do comply with the requirements. No verification is necessary. Situation is different if switches are part of an installation and used as repair and maintenance switch upstream of a frequency controlled motor. The frequency controller can emit interferences making necessary an electromagnetic shielding of the supply line. Of course in this case the switch must be integrated into the shielding. MERZ offers a complete range of EMC shielded enclosures in plastic and metal. Cam switches MN and compact switches ML are completely resistant and cannot be influenced by external interferences.

What is an Emergency stop switch?

With certain machines the main switch must fulfil the function of an emergency stop unit. In order to separate from standard functions the handle must be red whilst the background has to be yellow for safety reasons. The switching contacts of manually operated emergency stop units must be positively driven. Easy access in case of an emergency shut-down is a must whenever the device is fulfilling the function of an emergency stop switch.

What is an Extension shaft?

To adapt MERZ switchgear to various installation depths of switchboards and enclosures, a large range of shaft extensions is available for the MERZ cam switch series (MN) and the MERZ disconnect switch series (ML). Distances from 18mm to 405mm can be covered. Supports for big distances avoid a deviation of the extension shaft.

What is an Faulty signal resistance?

The ability of a contact to switch current and voltages without faulty signals. The contacts of cam and compact switches are designed for bigger currents and ratings, as a result small ratings can be transferred limited only. The critical values are 1A and 24V. In case of values smaller than the said ones gold plated contacts are recommended.

What is an Group switch?

The group switch is a sub-category of step switches. Whereas step switches make and break contacts separately per step, group switches allow maintaining the make for several switch steps. E.g. the light-bands in production halls are switched according to the illumination situation.

What is an IP Rating?

Relative to suitability for various ambient conditions electrical devices are classified in different degrees of protection, so-called IP-codes. The abbreviation IP according to DIN stands for „International Protection“, anyhow English speaking countries translate it as „Ingress Protection“. They are listed in the DIN EN 60529 with the header „Degrees of protection by means of enclosures (IP-code)“.

Degree of protection against dirt and touching (first digit)


Protection against touching
Protection against Dirt
0 No protection No protection
1 Protection against touching with back of the hand. The probe diameter is 50mm Protection against solid objects ≥ 50 mm
2 Finger Safe (test probe diameter ≥12,5mm and 80mm long) Protection against solid objects (diameter ≥12,5mm)
3 Protection against touching live parts with a tool/wire (diameter 2,5 mm) Protection against small solid parts (diameter ≥2,5 mm)
4 Protection against touching live parts with a wire (diameter 1 mm) Protection against small solid parts (diameter ≥1 mm)
5 Protection against touching with a wire like IP 4, but only small ingress of dust The ingress of dust is not totally prevented, but dust does not enter
in sufficient quantity to interfere with satisfactory operation of the
equipment or with safety.
6 Protection against touching with a wire like IP 4, dust-tight No entry of dust.
Degree of protection against water (second digit)


Protection against water
0 No protection
1 Protected against vertically dripping water
2 Protected against dripping water, when enclosure tilted up to 15°
3 Protected against sprayed water falling with up to 60° from the vertical
4 Protected against splashing water from any direction
5 Protected against water jets from any direction
6 Protected against powerful water jets
7 Protection against the effects of occasional submersion
8 Protection against the effects of permanent submersion

If one of the figures not needs to be mentioned it will be replaced by an „X“

Additional information is available in IEC/EN 60529

What is an Isolating function?

Function for complete power supply disconnection of a facility or part of it, whereas the facility must be completely separated from any source of energy for safety reasons. The position of the main contacts must be clearly and effectively displayed. The switch disconnector must be lockable in the OFF-position according to IEC/EN 60204-1. Increased requirements for actuators stability are based on IEC/EN 60947-3 in order to avoid, that the actuator can be moved to the OFF-position in case of welded contacts. IEC/EN 60947-3; 8.1.7

What are Line and cable entry points?

Line and cable entry points in housings and average values for the sealing zones of cable glands.

Pg = Steel Conduit Thread


Pg 9 11 13,5 16 21 29 36 42 48
Orifice diam. in mm 15,5 19 21 23 29 37,5 47,5 54,5 60
Outside diameter of lines and cables from - to mm 4,5 - 7 6 - 9 9 - 12 11 - 14 14 - 18 18 - 25 25 - 32 30 - 38 34 - 42
M = metrical
M = metrical
M.. x 1,5 mm
12 16 20 25 32 40 50 63
Outside diameter
of lines and ables
from - to mm
3 - 6,5 5 - 10 6 - 12 11 - 16 15 - 20 19 - 27 26 - 34 32 - 44


What is a Main switch?

IEC/EN 60204-1 is applicable for the safety and electrical equipment of machinery. The application of these normatives serves as well to achieve the safety aims of the EC machinery directive. A manually operated main switch has to be provided for every mains supply. As switch-disconnector it must comply with utilisation category AC-23 and fulfil following requirements:

- disconnecting the electric device of the mains, showing a single ON and OFF position each only, clearly marked with 0 and 1. In addition a triggered position is admissible.

- visible isolating distance or position indicator showing the OFF position only in case all contacts are opened in fact and a sufficient clearance according to the normatives is achieved. In case the main switch is not used as an emergency-off switch at the same time, red is excluded as its handle colour. Than black or grey are recommended colours.

- It has to be lockable in OFF-Position (e.g. by padlocks)

- All active conductors have to be disconnected of the mains. In TN net systems it is admissible to separate or not to separate the N-conductor.

- The rated breaking capacity has to be sufficient to break the current of the biggest motor in blocked state together with the sum of all operational currents of all other motors/consumers. However, the admitted rated thermal current has not to be exceeded!

- The handle of the main switch must be easily accessible and must be situated in a height between 0,6 and 1,9 m of the floor level.

What is a Metering switch?

Colloquially called voltmeter and ammeter selector switches, offered for the most different types of mains networks. The range MERZ offers with switches of series MN covers all possible variations.

What is a Multi-speed switch?

Multi speed switches are used for motors with 2 or more windings in order to vary the motor speed. There a several different versions available since the windings of such motors are either directly accessible via the motor terminal board or internally wired (Dahlander with tapped windings).

What is a Neutral conductor?

According to the German normative the neutral conductor might be switched, this without being a must. This differs e.g. of the situation in France. There the normative requires the disconnection of the neutral conduct of any equipment or machine equal to the other active conductors. This can be achieved by the MERZ cam switches (MN) due to their multitude of contact arrangements as well as by the MERZ compact switches (ML).

Corresponding to the series the contacts are else integrated in the basic versions or available as separate additional switch contacts for add on mounting. The switched neutral contact has to break after the other contacts and to make in advance of the other contacts! IEC/EN 60947-1; 8.1.9

What is a Norm?

All MERZ switchgear products are under steady inspection in our own test facilities. Beside that, all products have been tested by independent notified bodies and are subject to KEMA, UL and CSA approvals. Within Europe and the countries located at the Mediterranean Sea the notified bodies have agreed, that the testing must be performed according to the IEC/EN norms and is therefore mutually valid. Because of this regulation all MERZ switchgears are carrying the KEMA KEUR sign and are CCA certified which is documenting the international acceptance.

What is a On-Off switch?

Switch breaking or making one or multiple mains contacts simultaneously. Additional auxiliary contacts (NO/ NC) making/breaking as well in contrary can be included. Auxiliary contacts of series ML can carry up to 10A. Auxiliary contacts of series MN usually carry the same current as the main contacts. Exception is made at very large cam switches only, where a small auxiliary is coupled. (switch coupling).

What are Outside diameter of lines and cables?

Outside diameter of lines and cables.

3 cores - view technical data
Number of cores Nominal cross section
3 x 1,5 10 11 13 12,5
3 x 2,5 11 13 14 14,5
3 x 4 12,5 15 16 16
3 x 6 14 16 17 20
3 x 10 17 19 18 25,5
3 x 16 20 21 21 29
4 cores - view technical data
Number of cores Nominal cross section
4 x 1,5 10,5 13 14 13,5
4 x 2,5 12 14 15 15,5
4 x 4 14 16 17 18
4 x 6 15 17 18 22
4 x 10 18 20 20 23
4 x 16 23 23 23 32
4 x 25 27,5 27 28 37
4 x 35 31 30 29 42
4 x 50 - 35 34 48
4 x 70 - 40 37 54
4 x 95 - 45 42 60
4 x 120 - 50 47 65,5
4 x 150 - 53 52 -
4 x 185 - 60 60 -
4 x 240 - 71 70 -
5 cores - view technical data
Number of cores Nominal cross section
5 x 1,5 11 13,5 15 15
5 x 2,5 13 15 17 17
5 x 4 15 16,5 18 19
5 x 6 18 19 20 24
5 x 10 20 21 - 30
5 x 16 24 23 - 35
5 x 25 31 - - 41


NYM Light PVC-sheathed cable
NYY Cable with PVC sheath
NYCY Cable with concentric conductor and PVC sheath
NYCWY Cable with concentric, wavy conductor and PVC sheath
H07R‑F Rubber-insulated flexible cable for medium mechanical loading


What is an Overload?

Operating conditions that are causing an overload current within an electrically correct circuit.

What is an Permissible current load of lines?

Permissible current load and protection against overload of lines and cables for permanent installation at ambient temperatures of 25°C.

What are Polyamides (PA)?

finds application in the manufacture of unbreakable household items and technical parts where high abrasion resistance is required, such as dowels, screws, housings, bearings, insulation parts for electrical systems, cable ties, adhesive bases, etc.
Because of its resistance to lubricants and fuels at temperatures up to over 150 °C it is also used in vehicle manufacturing for parts that are built onto the engine such as suction systems, fuel pipes, engine covers etc.
The two most frequently used polyamides are PA 6 and PA 6.6. Their manufacturing process is fundamentally different. PA 6.6 and PA 6 are nevertheless chemically and physically very similar and differ only in their mirrored arrangement of one CH2-NH-CO group.

What are Polycarbonates (PC)?

are synthetic polymers from the polyester family. Polycarbonates are crystal clear, can be coloured, welded and glued and are also very dimensionally stable and possess high impact resistance.
Because of its higher cost relative to other plastics, polycarbonate is almost only used where others are too soft, too brittle, too prone to scratches, insufficiently dimensionally stable or not sufficiently clear. PC also excels for its high UV resistance and good electrical characteristics. MERZ uses PC for the enclosure series I7 and higher.

What is Polystyrol (PS)?

other names: polystyrene,
IUPAC name: poly(1-phenylethane-1,2-diyl)) is a transparent, amorphous or partially crystalline thermoplastic. PS can be dyed in all colours. Amorphous polystyrol is a common plastic that finds application in many areas of everyday life.
Polystyrol is used either as a thermoplastically workable raw material or as an expanded material. In electrical engineering polystyrol is used for its good insulating qualities. As well as for the insulation of cables it is used in the manufacture of switches, bobbins and housings (high-impact polystyrene, HIPS) for electrical equipment. Admittedly PS is only limited UV-resistant. Therefore it is not usable for outdoor use. PS is used for the production of the series 89xx and I1-S up to I3-S.

What is an Positively driven operation?

According to IEC/EN 60947-5-1 positively driven contacts must guarantee, that the contacts are completely opened as a direct result of a defined movement of a switch actuator without springloaded parts, when the actuator has travelled the forced disconnection travel at a manufacturer specified force.

What is an Pulse contacts?

Pulse contacts are used for additional triggering mostly of contactors or relays. In particular motor controls utilise
pulse contacts for activating an additional net-relay.

What is an Rated breaking capacity?

Rated value of current, a switching device can satisfactorily break corresponding to its utilization category. The rated breaking capacity is stated by reference to the rated operational voltage and rated operational current according to the relevant device norm. A switching device must be capable of breaking any value of current up to and including its rated breaking capacity. IEC/EN 60947-1;

What is an Rated conditional short-circuit current (of a circuit or a switching device) Iq?

From the manufacturer declared unaffected current, that a switching device (e.g. switch-disconnector), protected by a manufacturer specified short-circuit protective device (e.g. motor protection switch), can carry during the disconnecting time of such device under in the individual device norm specified testing conditions. The manufacturer must specify the details of the short-circuit protective device. IEC/EN 60947-1;

What is an Rated impulse withstand voltage Uimp?

Peak value of an impulse voltage at a specified form and polarity under which the switching device can be stressed at specified testing conditions without malfunction and whereas the sparking distance is referred to. The rated impulse withstand voltage of the switching device must meet or exceed the impulse overvoltage (transient overvoltage) that may occur in the circuit the device is operating in. IEC/EN 60947-1;

What is an Rated insulation voltage Ui?

The rated insulation voltage of equipment is the value of voltage to which dielectric tests and creeping distances are referred to. The maximum rated operational voltage by no means can be higher than the rated insulation voltage. IEC/EN 60947-1;

What is an Rated making capacity?

Rated value of current, a switching device can satisfactorily make corresponding to its utilization category. The rated making capacity is stated by reference to the rated operational voltage and rated operational current according to the relevant device norm. IEC/EN 60947-1;

What is an Rated operational current Ie?

Rated current a switching device can carry in uninterrupted duty, taking into account rated operational voltage, rated frequency, rated operational mode, utilization category and ambient temperature. IEC/EN 60947-1;

What is an Rated operational voltage Ue?

Voltage of a switching device, which, together with the rated operational current, determins the application of the device and where all the different examinations and utilization categories are referred to. For single pole devices the rated operational voltage is in general the voltage over the pole. For multiple pole devices it is in general stated as chained voltage. IEC/EN 60947-1;

What is an Rated short-circuit breaking capacity Icn?

Short-circuit current a switching device can break at the rated operational voltage and frequency at a defined power factor for AC or a defined response time for DC applications. It is expressed by the maximum peak value of the unaffected current, that such device can break under specified conditions. IEC/EN 60947-1;

What is an Rated short-circuit making capacity Icm?

Short-circuit current a switching device can make at the rated operational voltage and frequency at a defined power factor for AC or a defined response time for DC applications. It is expressed by the maximum peak value of the unaffected current, that such device can make under specified conditions. IEC/EN 60947-1;

What is an Rated short-time withstand current Icw?

Short-time current that a switching device can carry under, in the individual device norm specified, test conditions without being damaged.
IEC/EN 60947-1;

What is an Rated uninterrupted current Iu?

For switching devices in switchboard installation Iu=Ith. For switching devices in an enclosure Iu=Ithe . Current a switching device can carry in uninterrupted duty (for weeks, months or even years). IEC/EN 60947-1;

What is REACH?

(Registration, Evaluation, Authorisation of Chemicals)
EU-Directive No.1907/2006,18. December 2006
REACH rules the use and handling of substances (chemicals) on their own, in preparations and in articles. REACH covers all (chemical) substances, doesn’t matter whether they are dangerous or not. On the side of the industry the following companies located in the EC must take actions according REACH:

• Producers (of chemicals)

• Importers (who bring chemicals into the EC)

• Downstream user (user of chemicals)

• Traders (of chemicals)

MERZ Schaltgeräte GMBH + CO KG is not producing chemicals or importing chemicals from non EU countries. Therefore we are not obliged to pre-register any substances at all. Based on the information we received from our suppliers, we expect that all substances we use are pre-registered in time.


What are Recommended values for three-phase squirrel-cage motors with 1500 rpm at 50 Hz?

Rated motor currents as quoted are for normal internally and surface cooled motors. Fuse: slow-blow or gL characteristic with specified lowest possible short-circuit fuse Direct start-up: max. start-up time 5 s, max. start-up current 6 x rated motor current Y start-up: max. start-up time 15 s, max. start-up current 2 x rated motor current.

What is an Repair and maintenance switch?

Repair and maintenance switches are used to safely shut down machines and facilities that are not directly connected to a control unit or may bare the risk, that the machine or facility starts operating during maintenance or repair activities. The handle of such switches must be lockable by interlocks in order to prevent workers from hazardous situations and must meet the same requirements as main switches according to IEC/EN 60204-1

What is an Reversing switch?

Reversing switches are used to change sense of rotation of AC motors. While switching from 1 over 0 to 2 two phases of the three phase alternating current net are interchanged in order to start the motor in the opposite direction. A typical application is the switching option W___/3. where all three phases of a motor are completely separated from the net in 0-position. In the next step the motor is switched on with two interchanged phases.
For motor-starter-combinations, where a net disconnector is used in front of the reversing switch, also 2 phases are interchanged. However, in this case the third phase is directly wired (switching option W___/2.). This switch is more compact but, as long as the net disconnector is not shut-off, continuously carries a load at the motor via the third phase.
Reversing switches are available with or without „0“-position. Also versions with both-sided automatic retraction in „0“-position are available.

What is RoHS?

EU standard 2002/95/EG (updated 21/10/2005)
The main contents are listings of banned substances no longer allowed to be a component in the products after the 01.07.2006. Limit values for that substances are set for Germany in the draft of the „ElektroG” dd. 01.09.2004. In 2003 MERZ GMBH already started to identify the relevant banned substances in the affected products. MERZ was determining and testing alternative substances.
Today MERZ products fulfil the requirements of the standard completely. We did not change the article numbers for the individual products.
Starting from 1. April 2006 we certify the conformity of our products affected by that standards according to the updated version of that regulation valid from 21.10.2005.


What is an Safety switch?

Safety switches are encapsulated main- repair or maintenance switches where the housing cannot be opened while the handle is locked by a padlock in OFF-position. MERZ safety switches are realized with the enclosure series I1 to I3.

What is an Single-phase starter switch?

Single-phase starter switches are used for starting of single-phase AC-motors. There are versions available for unidirectional or bidirectional motors with and without starter capacitors.

What is an Star-Delta switch?

Star-Delta switches are needed to start larger three-phase alternating current motors with short circuit rotors rom 4kW upwards. The public power distribution network (230V/400V) does not allow start-up current higher than 60 Amps according to the TAB regulation. Motors with a capacity rating above 4 kW are therefore subject to a current limiting start-up mode. Such method prevents fuses to blow-up and potential voltage drops caused
by a very high start-up current in a direct switching mode. Star-Delta switches are offering the most compact and cost effective solution. There are versions with one or two rotating directions available. Furthermore the switches can be equipped with additional impulse mode contacts in order to activate or control additional contactors.

What is an Step switch?

Step switches provide the widest offering in the MERZ MN product range. The switches are available from 3 to 12 positions with and without 0- position. All switches are available in 1-, 2- or 3-pole versions. Step switches are always activating one (respective 2 or 3 for 2- or 3-pole versions) contact only while switching from one position to the next whereas this contact will be disabled once the switch is moving to the successive position. There is no overlapping from one contact to the next during the changeover phase.

What is an Switch disconnector?

Switch disconnectors are mechanically operated switches in a circuit which are able to make, carry and break under normal operating conditions currents including a specified overload. In the open position the contacts fulfil the requirements of a disconnector. IEC/EN60947-3

What is an Switch with spring-return?

In many applications it is necessary to control the machines and facilities by impulse or inching modes. In order to ensure that the device is not switching into constant modes MERZ has designed cam switches in such way, that the handle and the related switching contacts automatically move back into the starting position once the handle is released. Typical examples are lifts, where the switch must be held until the upward or downward
movement has reached its wanted position or with pumps, that are usually operating only in one direction but may have to temporarily change directions i.e. for cleaning mode.

What is an Under Voltage Release?

The MERZ UVR-Switches with undervoltage release are available for a power range from 32A - 63A. The undervoltage release switch (UVR) is an electromechanical device which automatically shuts down when the supply voltage falls below a certain value. In such case the handle moves back to the OFFposition. The switch has been designed to open its contacts (release-free) even though the handle is eventually blocked. The undervoltage release is required in many countries especially for machines with rotating tools.

What is an Utilisation categories?

Utilisation categories describe the application of switching devices, referring to load limit values set by the normatives. Differentiation is made between utilisation categories for „AC“ and „DC“. MERZ switchgear are applicable for AC and 3-phase current and designed and tested to the strictest AC categories AC-3, AC-22 and AC-23. As a result they are suitable as well for other „AC“ categories. Code letter „A“ and „B“ placed after the utilisation category refers to the used testing cycle within the respective test. „A“ in general names the more demanding test cycle as the switch has to survive more switching cycles. IEC/EN 60947-1

Utilisation category - Typical application


AC-1 Non-inductive or weakly inductive loads, resistance furnaces
AC-2 Slipring motors; startup, shut-down
AC-3 Squirrel-cage motors; startup, shut-down
AC-4 Squirrel-cage motors; startup, reactive braking or reversing, inching
AC-15 Control, electromagnetic loads with alternating-current voltage
AC-20 Switch-on and switch-off at no load
AC-21 Switching ohmic loads including moderate overload
AC-22 Switching mixed ohmic and inductive loads including moderate overload
AC-23 Switching motor loads or other heavily inductive loads