turck articles

Industrial Relays MRC QRC IRC

TURCK 9/11/2018
Industrial Relays MRC, QRC, IRC

Product range
Releco offers a wide range of relay types and versions and associated sockets and accessories.

Standard (general-purpose) relay, MRC series
35 x 35 mm round plug-in relay, 8- or 11-terminals multipole connector according to IEC 67 with 2 or 3 contacts up to 10 A and different contact types and contact materials. Standard relay 35 x 35 mm with flat blade connectors with up to 4 contacts and up to 16 A with 3 contacts.

Miniature industrial relay, QRC series
22.5 mm series with up to 4 contacts and up to 10 A with 1 or 2 contacts.

Interface relay, IRC series
Overall width 13 mm with up to 2 electro-mechanical contacts, or fully electronic switches.

Special relays, remanence relays
While "normal" relays are monostable, i.e. they return to the idle state when the excitation is switched off, remanence relays are bistable, i.e. the current switching state is retained irrespective of the excitation. Relays of this type are available in different versions.

Electronic relay, CSS
In the Comat Releco IRC series different electronic DC or AC relays up to 6 A are available. For AC relays a distinction is made between synchronously (zero crossing) and asynchronously switching versions. For switching transformer loads we recommended using asynchronously switching semiconductor switches. For incandescent lamp loads etc. synchronously switching switches are ideal for avoiding high switch-on currents.

Suitable sockets are available for the different relay series for DIN rail mounting or panel mounting. In addition, retaining clips are available for the relays, some of which are included in the scope of supply. Suitable bridges for cost-saving wiring in series are also available.

* Special requirements
H = Orange button. No lockable function
N = Black button. No function
P =  Printing board pins
E =  Lap transparent cover
Z =  Close transparent cover
T =  Close transparent cover (lamp)
M = Close transparent cover (lamp + button)
If other requeriments, please consult.

Protection against transients
When the coil is disconnected from an electro- magnet, peaks of inverse voltage appear at the terminals which can reach very high values. These pulses can be transmitted down the line associated with the coil and could possibly affect other components. In the case of a realy being operated by such devices as transistors, triacs, etc; it may be necessary to protect against transients.

Transients carried in the line
High voltage surges can be carried in the sup- ply line to the relay coil. These may appear in the form of peaks or bursts and are generated by the connection and disconnection of elec- tric motors, transformers, capacitors etc. Normally a relay is unaffected by these pulses, but if a diode is connected in association with the coil, it must be capable of withstanding an inverse voltage higher than those of the incoming peaks.

Protection circuits
A protection circuit must efficiently cope with pulses generated by the coil as well as inco- ming line surges (surges U1,2/50µs.) Releco relays are available with integrated pro-tection circuits or with modules plugged into sockets S3-MP or S3-MS.

Industrial Relays MRC, QRC, IRC

X        LED indication with rectifier.
For DC and AC relays up to 250 V
Surges of 1000 V up to 24 V
Surges of 2000 V from 25 to 60 V
Surges of 4000 V from 61 to 250 V
Note: LED connected, in series with the coil @220 VDC in QRC types.

D        Free-wheeling diode.
DX       Free-wheeling diode + LED
Dampens transients caused by the relay coil on de-energisation.
Surges of 2000 V up to 60 VDC
Surges of 4000 V from 61 to 250 VDC (*)

F        Polarity + free wheeling diode.
FX       Polarity + free wheeling diode + LED
A diode in series with the coil protects the relay from reverse connection.
Surges of 1000 V up to 60 VDC
Surges of 4000 V from 61 to 250 VDC (*)

B        Bridge rectifier incorporated
BX       Bridge rectifier + LED indication Allows the relay to operate in both AC or DC without any polarity inconvience.
Available only in voltages up to 60 V.
Surges of 1000 V

R          Resistor and capacitor.
Suppressor for AC coils.
Surges of 2000 V.
Available only in MRC types.
(*) Surges  of 2000 V in QRC types.

Industrial Relays MRC, QRC, IRC


LED and protection circuit connected to coil.

X      LED with no polarity, (standard)
Coils ≤ 12 V CC y CA
LED rectifier bridge in parallel
X      LED with no polarity, (standard)
Coils ≥ 24 V … CC y CA
LED rectifier bridge in series
FX    LED with polarity A1+ (option)
Every DC coil voltage
Polarity and Free-wheeling diodes
BX   LED with no polarity, (option)
Only 24 V and 48 V ADC coils
Rectifier bridge for AC/DC relays
R      LED not available (option)
RC protection against pulses on AC

Protection against pulses
When a relay coil is disconnected, reverse voltage peaks may arise and reach very high values. Said peaks can transmit to the coil associated line and other relays or semiconductors can be affected.

If triac, transistor, etc. controls a relay, appropriate steps must be taken to avoid or decrease peaks down to a non risky level.

Both Polarity and Free-wheeling diodes (FX), must protect coils, to avoid malfunctions provided DC relays in battery are installed.

Making or breaking engines, transformers or contactors in an industrial environmental, may generate high voltage pulses, either isolated or burst, through the main line. The voltage level of those pulse may be high enough to affect the isolation of the coil.

Industrial Relays MRC, QRC, IRC
There are different contact types. The main distinction is between single contacts and twin contacts. While single contacts are more suitable for higher loads, twin contacts are significantly more reliable at small loads, i.e. < 24 V, < 100 mA.

Contact Material
There is no all-purpose contact! AgNi is used as standard material for a wide range of applications. AgNi contacts with hard gold plating (up to 10 µm) are offered for appli- cations in aggressive atmosphere. Relays with gold contacts are approved for relatively high currents (e.g. 6 A, 250 V), but in practice values of 200 mA, 30 V should not be exceeded for operation with intact gold plating. Relays with a tungsten pre-contact are available for very high switch-on currents (up to 500 A, 2.5 ms). For some applications AgNi contacts with gold flashing (0.2 µm) are available. The purpose is corrosion protection during storage. There is no other purpose. Tin oxide is specially appropiated for load with high-inrush current.

Minimum load
The minimum load value is a recommended value under normal conditions such as regular switching, no special ambient conditions, etc. Under these conditions reliable switching behaviour can be expected.

Contact resistance
Initial values of resistance of contact can vary with the use, load and others conditions. Typical values when the relay is new is about 50 mΩ.

Contact spacing
Normally all contacts have an air gap between 0,5 ... 1.5 mm when they are open. They are referred to as µ contacts. According to the
Low-Voltage Directive and the associated stan- dards these contacts are not suitable for safe disconnection. For switching of DC loads large contact clearances are beneficial for quenching the arc. See special relays: series connections  with a gap of 3 mm.

Switching capacity
The contact switching capacity is the product of switching voltage and switching current. For AC the permitted switching capacity is generally high enough to handle the max. continuous AC1 current over the whole voltage range. For DC the load limit curve must never be exceeded, because this would lead to a remaining switch-off arc and immediate destruction of the relay. The order of magnitu- de of the DC switching capacity is a few 100 W (DC 1).

Drive (coil)
The drive of a relay refers to the coil plus connections. The coil has special characteristics, depending on the rated voltage and the type of current.

Coil design
The coil consists of a plastic former (resistant up to about 130 °C) and doubly insulated high-purity copper wire, temperature class F. The winding must withstand threshold voltages (EN 61000-4-5) of more than 2000 V. This is ensured through forced separation of the start and end of the winding.

Coil resistance and other properties
Each coil has an ohmic coil resistance that can be verified with an ohmmeter. The specified coil resistance applies to a temperature of 20°C. The tolerance is ± 10 %. For AC operation the coil current will not match the ohmic value, because self-inductance plays a dominant role. At 230 V this may reach more than 90 H. When a relay is switched off, self-inductance results in a self-induced voltage that may affect the switching source (destruction of transistors, EMC problems).

Drive voltages
A distinction is made between the standardised voltages according to EN 60947 as gua- ranteed values, and typical values that can be expected with a high degree of probability.

Pick-up voltage, Release voltage
The pick-up voltage is the voltage at which the relay engages safely. For DC the typical trip voltage is approx. 65 % of Unom, for AC approx. 75 %. The release voltage, on the other hand, is approx. 25 % or 60 % respectively. For DC these voltages are strongly temperature-dependent, according to the temperature coefficient of Cu. This is not the case for AC, where the inductive resistance is the controlling factor, which is practically constant over a wide temperature range. With AC, in a certain undervoltage range the relay may hum, and the armature may flutter. This voltage range must be avoided.

Operating voltage range
Unless specified otherwise, the following characteristic curve applies for the operating vol- tage range. The upper limit of the coil voltage is determined by self-heating and the ambient temperature. Self-heating through contacts under high load must not be underestimated. It may be higher than the power dissipation in the drive. During intermittent operation significantly higher overvoltages temporary may occur for short periods. If in doubt please consult our specialists.

Miniature industrial relay, QRC series

General design
Comat RELECO relays are made from high-quality, carefully selected materials. They comply with the latest environmental regulations such as RohS. Their meticulous design makes them particularly suitable for industrial applications and installation engineering. They are particularly service-friendly through robust terminals, mechanical position indicating device a standard, manual operation, dynamic, permanent characteristics. Colour coding for manual operation as a function of the coil voltage is another useful feature. Further options such as different coil connections, freewheeling diode, LED display, bridge rectifier for AC/DC drives etc., and short-term availability of special versions for practically any drive voltage up to DC 220 V / AC 400 V leave nothing to be desired. Apart from a few special versions, the standard Comat RELECO industrial relays feature manual operation (push/pull) and a mechanical position indicating device. For safety reasons, manual operation may be replaced with a black button, if required.

Coil connections
Different coil connections can be integrated in the relay as an option. For DC a cost-effective freewheeling diode is available. Please note that the stated release times are generally specified without the coil connection. While an additional LED status indicator has practically no effect, a freewheeling diode (D) will lead to an increase in release time by a factor 2 to 5, or 10 ms to 30 ms. For AC VDRs or RC elements may be used. In this case resonance effects may have to be considered. VDRs and common RC elements may increase release times by less than 5 ms.

Industrial relays MRC, QRC, IRC
Standards, conformities
While CE marking of relays/sockets is controversial, since relays are sometimes regarded as components to which the marking requirement does not apply, all RELECO relays feature the CE mark to indicate that CE standards may also be applied to the relays, e.g. 2 kV surge resistance according to EN 61000-4-5. A significant and not generally available characteristic is that the coils and in particular the connections are able to withstand the voltage spikes that may occur in practice. In addition, the relays feature various technical approvals depending on the respective relay code, and they comply with further standards and guidelines. The main technical approvals include cURus, CSA, and CCC. The associated information is provided in the respective data sheets.

Switching classes
EN 60947 defines different switching classes that specify the suitability of contacts for different load types.

AC1 = Ohmic AC load
AC5b = AC incandescent lamp loads AC15 = Power contactors, solenoid valves, solenoids
DC1 = Ohmic DC load
DC6 = DC incandescent lamps
DC13 = DC contactors, solenoids

UL508 contains different technical approval criteria such as general purpose, control application etc. Switching classes are defined based on the electrical switching capacity, e.g. B600 etc.

Main technical approvals and standards

Miniature industrial relay, QRC series

Utilisation categories according to EN 60947-4-1/-5-1

Pollution category

Cat. 1
Dry, non-conductive contamination without further effect
Cat. 2
Occasional conductive contamination, short duration due to moisture condensation
Cat. 3
Dry, non-conductive and conductive conta- mination with moisture condensation
Cat. 4
Contamination with persistent conductivity through conductive dust, rain

Protection class IP
according to DIN 40050 and other standards. Industrial relays and their sockets can be classified as follows: Socket IP20: Contact safety Relay IP40/IP50: not watertight, but protected against ingress of coarse contaminants.

Further information and tips
The main operational criteria for relays such as number of cycles, switching frequency, ambient conditions, reliability requirements, load type, switch-on current, load switch-off energy must be clarified in order to ensure reliable operation and long service life.

If the number of cycles is expected to exceed several 100,000 operations per year (e.g. clock generators, fast running machines), an electronic solution is no doubt more appropriate, although we also offer solutions for this type of application.  In AC applications crosstalk caused by long control leads is often problem and can result in constant humming of the relay or even inad- vertent triggering due to interference. Here, too, we offer solutions.

Various, apparently harmless loads may lead to very high switch-on currents or switch-off energy values, resulting in an unacceptable reduction in service life. Particularly tricky are DC loads, particularly if they are inductive. Circuits with relays and their connections often require a level of developer skill that is frequently no longer offered during standard education and training. Your supplier will be very happy to provide expert advice

Characteristics of various loads:

Heating circuits
No higher switch-on currents, no higher switch-off loads.

Incandescent lamps, halogen lamps
Switch-on currents during a few ms in the range 10 ... 18 x rated. Switch-off at rated load.

Low-energy lamps
Very high, but very short switch-on currents due to built-in decoupling capacitors. Contacts have a tendency to fuse.

Transformers, AC contactors
Switching on during zero-transition may lead to switch-on currents of 8 ... 15 x rated. High inductive switch-off energy is possible. The load must be connected, not least due to EMC problems.