Thermocouple cables ТЕРК (in acc. with ТУ 3567-015-76960731-2009)

ThERmocouple Cables TERC are designed to connect thermocouples to the secondary transducers (temperature measuring means).
In order to substantially eliminate the influence of the operating mode of the object (e.g., a heating furnace) at the temperature of the free ends of the thermocouple ther is need to remove them from the heating space for a considerable distance. This does not necessarily requires to apply long thermocouple, it is better to lengthen them with flexible cables. These cables should be thermoelectrically identical to thermoelectrodes of the thermocouples, due to that they are called thermocouple cables.
Thermocouple cables TERC are divided into extension and compensation:

1. EXtension cables – cable conductors are made of the same alloy as the thermocouple. Extension cables, unlike thermocouples, operate in a narrower temperature range. Within the cable designation after the specified type of thermocouple (acc. to ГОСТ 50342-92 or IEC 584-1) is added the symbol «X», for example: «NX» - an extension cable for thermocouple pf N type (made of nichrosil-nisil). The «X» symbol is derived from the English term «eXtension cable». At a predetermined temperature range the electrodes (conductors) of these cables develop in tandem with the third electrode (eg, copper or platinum) the same thermal EMF as thermocouple respective electrodes. Therefore, extension cables are called cables with electrode-wise compensation.
2. Compensation cables – cable conductors, compared with the extension cables ones are made of less expensive or precious metals. For example, for a thermocouple of K type (chromel-alumel) is used the compensation cable with conductors made of copper (positive) and constantan (negative). The application of compensating cables can also be caused by the need to have a minimum resistance of the circuit. Compensation cables are developing thermos EMF equal to the thermal EMF of the thermocouple, for which they are intended, and therefore they are called total compensation cables. Within the compensation cables designation after specifying the type of thermocouple (acc. to ГОСТ 50342-92 or IEC 584-1) the symbol «C» is added, and if there are two versions of the cable that provided for thermocouple - the symbol «CA» or «CB». For example, the "КСА" – is the compensation cable according to IEC 584-3 standard for thermocouple of K type (chromel-alumel). «C» symbol is derived from the English term «Compensation cable». Compensation cables, in comparison with extension cables are characterized by a narrower range of operating temperatures and higher values of tolerances.

Two standards of TERC cable manufacturing

Cables TERC can be manufactured in one of the two options and comply with the standards:

1. The cables labelled as KX, KCA, KCB, NX, EX, JX, TX, SCA, SCB, RCA, RCB are manufactured under the international standard изготавливаются по международному стандарту IEC 584-3 «Thermocouples. Part 3: Extension and compensating cables – Tolerances and identification system» (см. таблицу 2). В The standard establishes the requirements for limited deflection of thermocouple pair thermal EMF, as well as the colour of core insulation and outer sheath of the cable. The cables TERC made under the IEC 584-3 standard makes sense to use with thermocouples manufactured according to international standard.
2. The cable conductors labelled as XA(KX), ХA(KC), XКн(EX), ЖК(JX), ХК(LX), МКн(TX), ПП(SCA), ПП(SCB), ПП(RC), ПР(BC), МК(MX) are made of metals or alloys in accordance with national Russian and intrastate standards: GOST 1791-2014, GOST 492-2006, GOST 859-2014 and others. At the standard GOST 1791-2014 there are established tolerance classes for the thermos-EMF of the wire, which is used for cable conductor, and made of the alloys: chromel K, copel, constantan, TP. A colour of core insulation and outer sheath for the thermocouple cables is not defined by any of the national standards, but in the TERC cables there is in use conductor insulation colours common for Russia (see. Table 3). The cable jacket can be of any colour (by default - black).

Application range

The cables are designed for fixed and mobile laying indoors and outdoors if protected from direct exposure to solar radiation, on shelves, in trays, ducts, channels, tunnels, earth (trenches), in places exposed to stray currents. The cables with "UV" coding can be installed outdoors unprotected from the sun radiation. The cables of "M" performance have got a jacket resistant to engine oil, gasoline and diesel fuel. The cables of "V" performance is protected to the spread of water under the jacket.
Fire-resistant cables «FR» have got the top fire resistance PO1 according to GOST 31565-2012 and are able to operate in a fire conditions at least 180 minutes.
The cables with extruded filling "z" have a circular cross section and prevent the spread of potentially explosive gases under the jacket. These cables fully comply with the technical regulations of the Customs Union TR CU 012/2011 "On safety equipment for use in potentially explosive atmospheres" and GOST IEC 60079-14-2011 «Explosive atmospheres. Part 14: Design, selection and mounting of electrical installations ", and can be used in hazardous zones of all classes.

The operating temperature of cables is shown in Table 6, the temperature depends on the insulation and jacket material. Preferred areas of application of TERC cables taking into account the type of performance and fire hazard class in accordance with GOST 31565-2012 are shown in Table 7.

TERC cable design

The cable conductors are made of metal and alloy or two alloys in accordance with the Table 2 (standard IEC 584-3) or Table 3 (national standards).
The conductors are manufactured stranded (default) or single-wire ("ozh" index). The cables labelled "G" are made with strands of increased flexibility.
The conductor of fire-resistant cables «FR» before the insulation imposition is wound with mica tapes, it provides maximum cable resistance to mechanical stress in case of fire.
The wires in the cable can be manufactured in a twisted pair of thermocouple, in this case, the symbol «x2» is added to the number of pairs in the order code.
Cables can be produced with the combined cross-section of conductors (such as «2х1,5 + 4х1,0» or «1х2х1,5 + 2х2х1,0»).

Digital marking is applied to all the cores of a cable of the same colour.

The cables can have a shield: individual one of each pair and / or the total one of all pairs.
Shields can be made as:

• Aluminium-foiled tape (AlumoFlex) with drain tinned copper wire "E",
• braid made of untinned copper wire «Em»,
• braid made of tinned copper wire «El»,
• braid made of nickel wire «En».

Individual shields of couples can be electrically isolated between each other by a extruded polymer layer as well as can be fabricated as combined type "EEl" - on a top of the AlumiFlex shield a braiding of tinned copper wires is imposed.

The cables can have got an armor as:

• made of zinc-coated steel wires «K», the outer sheath is imposed upon armor;
• made of zinc-coated steel tapes «B», the outer sheath is imposed upon armor;
• made of stainless steel wires «Kn», the outer sheath is imposed upon armor;
• made of stainless steel tapes «Bn», the outer sheath is imposed upon armor;
• tank armor of zinc-coated wire "Kp" is over the inner shell, the outer sheath is not imposed;
• tank armor of stainless steel wire "Knp" is over the inner shell, the outer sheath is not imposed;

Cables with a single thermocouple pair can be made in a flat version "P". Table 6 shows the materials of insulation and sheath, as well as the corresponding fire safety performance coding.

Table 1. Core nominal cross section and the number of cores or pairs:

Material alloy of conductors, colour of core insulation and outer sheath for TERC cables on the standard IEC 584-3: with marking KX, KCA, KCB, NX, EX, JX, TX, SCA, SCB, RCA, RCB
The colour of negative core insulation for TERC cables should be white as of the standard IEC 584-3. The colour of the positive core insulation should comply with Table 2. The colour of outer sheath should be as the positive core one. Cables are designed for intrinsically safe circuits shall be permitted to make with a sheath of light-blue (blue) colours.

Table 2. The material and colour of the core insulation for TERC cables as of IEC 584-3:

Core alloy material, core insulation and outer sheath colour for TERC cables as of the national standards: marked as XA(KX), ХA(KC), XКн(EX), ЖК(JX), ХК(LX), МКн(TX), ПП(SCA), ПП(SCB), ПП(RC), ПР(BC), МК(MX)
The core insulation colour for TERC cables, as it’s customised in Russia, is designating metal or alloy applied (see Table 3). In agreement the other colours of insulated cores are allowed.
In Russia, there is no stricken requirement for the colour of the cable jacket, so TERC cables are available by default with black jacket. Provided there is a need for other jacket colour, it should be stipulated at the order code.

Table 3. Material and colour of core insulation for TERC cables as of the national standards

* thermocouple of L type as of GOST R 50342-92, not to be mixed with thermocouple of L type as of DIN 43710 (Fe-CuNi)

Tolerance classes and limit deviation limits of thermal EMF (TEMF) Tolerance class characterises the allowed deviations limit of TEMF. As of standard IEC 584-3 the tolerance classes are defined for thermocouple pair of a cable, while as of GOST 1791-2014 – for the wire, which is used for the core manufacturing paired with the copper sample. For some cables the tolerance class is defined for the wire paired with the platinum sample. Provided there is no specific notes regarding the tolerance class, the TERC cable class is defined by a manufacturer choice – generally it’s an alloy with the 2nd tolerance class.

1. Tolerance classes for TERC cables as of standard
IEC 584-3: сlabelled as KX, KCA, KCB, NX, EX, JX, TX, SCA, SCB, RCA, RCB
In the international standard IEC 584-3 the cable tolerance class determines the deviation limit of TEMF measured in mkV and degrees Celsius within the certain cable operating temperature range (Table 4). Since TEMF nonlinearly depends on the temperature, the tolerance value in degrees Celsius is given for a specific operating temperature of a thermocouple junction.
For cables there was established only 2 tolerance classes. Extension cables (with the symbol "X") may be made as of class 1 and 2, and compensation cables (with symbols «C», «CA», «CB») - only as of the 2nd tolerance class.

Table 4. TEMF deviation limits for TERC cables as of standard IEC 584-3

2. Tolerance classes for TERC cables as of GOST 1791-2004: cables labelled as ХА(KX), ХКн(EX), ЖК(JX), ХК(LX), МКн(TX), МК(MX), ХА(KC), ПП(SCA), ПП(RC)
GOST 1791-2014 determines 2 tolerance classes for wire, which is used for the thermocouple cable core manufacturing, alloys: chromel К, copel, constantan, TP (see Table 5). Tolerance class is determined for the wire paired with the copper sample at temperature 100°С (free end at 0°С). TEMF deviation limits are determined mkV for each tolerance class. The wire made of TP alloy has got deviation limit as of ± 0,03 mV.

Table 5. TEMF deviation limits for a wire which is used for TERC cable manufacturing as of Russian (intrastate) standard GOST 1791-2014

Table 6. Fire safety performance coding and operating temperature depending on the sheath and the insulation material

as «HL» performance with operating temperature down to minus 60°С

Table 7. Major application range for TERC cable according to performance type and fire safety performance coding as of GOST 31565-2012

Table 8. Allowed TERC cables bending radius