• Conductor

                        Plain Annealed Copper/Tinned Copper (Class 1/Class 2/Class 5)

  • Insulation

                        PVC/XLPE/HDPE/LSFOH/SR

  • Metallic Screen

            Individual Screen (ISCR)/Overall Screen (OSCR)/Copper Braid Screen (CWB/TCWB)

  • Inner Covering (Bedding)

                        PVC/LSPVC/LSFOH/PE (HDPE)

  • Protection Sheath

            Lead Alloy Sheath/ALC Sheath (Aluminum Copolymer)

  • Separation Sheath (Bedding)

                        PVC/LSPVC/LSFOH/PE (HDPE)

  • Armour

                        Round Wire Armour (SWA)/Double Tape Armour (STA)/Wire Braid Armour (SWB)

  • Outer Sheath

                        PVC/LSPVC/LSFOH/PE (HDPE)

– Instrumentation and control cables are suitable for use in Oil, Gas, chemical and petrochemical plants, iron and steel industries, Off-Shore…

International standards normally prescribe materials, constructions, performances, but in many cases instrumentation and control cables have to be designed and manufactured according to specific requirements.

– Instrumentation Cables mostly operate at voltage levels of 24 to 500 v and/or at 4-20 mA current rating. They are used to transmit and receive control system, analogue and digital signals to and from sensors and equipment. They are deployed across a wide range of industries, including power generation and distribution, and the petrochemical industry.

– Instrumentation cables are used in data processing and process control and are suitable for installations in open spaces and for underground laying. For digital signals and solenoids, overall screened type and for analogue signals between junction boxes and electrical room/control building, individual and overall screened type may be applied.

Conductors

For instrumentation cables conductors are generally Plain Annealed Copper or Tinned Copper.

Conductors can generally be according to IEC 60288:

  • Class 1 (Solid)
  • Class 2 (Stranded)
  • Class 5 (Flexible)

Insulation

Many materials can be used as insulation for LV Power cables: working conditions need to be taken into consideration to choose the right material.

Material can be divided into two classes: Thermoplastic and Thermoset (Cross-Linked).

Thermoplastic material is more sensitive to high temperatures, as material melts at the increase of temperature, while thermoset, due to stable polymeric chain bonds are more resistant to temperature and deformation.

In the first class there are the most popular insulations for these types of cables such as PE and PVC for general installation conditions and the new generation of LSFOH thermoplastic materials (low smoke and zero halogen).

Second class includes, for example, XLPE, silicone rubber, other rubbers such as EPR, HEPR, EVA.

Special techno polymer can be used in case of specific installation condition, such as fluoropolymer or techno polymer materials.

For fire resistant cables two types of insulation are used: silicone or mica glass tape plus XLPE (or other thermoset compounds).

Cabling

Instrumentation cables can be laid up in:

  • Concentric construction
  • Pairs
  • Triples
  • Quads

In case of quads, this is normally considered a two-pair element, the connection is done using opposed cores for one circuit.

Twisting is important to reduce noise in circuits and also the lay of twist in some constructions must be carefully considered.

In some application, in order to reduce interference between cabling elements, the length of twist of adjacent elements (pairs) must be different. With individual screen on each element, the above is not necessary.

Communication wire or couple can be added to total cabling of elements, if required.

Metallic Screen

Screens are often used in instrumentation cables to prevent or reduce possible interference in cables that can be caused by the following reasons:

  • Cross-talk from adjacent pairs or triples;
  • Interference induced by external source such as electrical equipment, machinery and power line.

Screens can be:

Individual Screen (ISCR)

Aluminum/polyester tape or Copper/polyester tape with a tinned copper drain wire, the most popular construction.

Aluminum/polyester or copper/polyester tapes normally have a total thickness from 25 to 100 μm, according to standards and are wrapped with an overlap > 125% to assure a full coverage even in case of bending.

In continuous contact with metallic side there is a drain wire, normally tinned copper, 0.5 sqmm, stranded or solid.

Overall Screen (OSCR)

Aluminum/polyester tape or Copper/polyester tape with a tinned copper drain wire, the most popular construction.

Aluminum/polyester or copper/polyester tapes normally have a total thickness from 25 to 100 μm, according to standards and are wrapped with an overlap > 125% to assure a full coverage even in case of bending.

In continuous contact with metallic side there is a drain wire, normally tinned copper, 0.5 sqmm, stranded or solid.

Copper Braid Screen

for electromagnetic interference or when the cable is subject to movements.

Copper braid normally has a coverage from 80% to 95%. This type of screen presents a lower electrical resistance, a very good protection also to electromagnetic noises and a higher mechanical resistance compared to aluminum/polyester tape. It is suitable for mobile applications.

Tinned Copper Braid Screen

for electromagnetic interference in presence of corrosive atmosphere or high temperature. Tinned Copper braid normally has a coverage from 80% to 95%. This type of screen presents a lower electrical resistance, a very good protection also to electromagnetic noises and a higher mechanical resistance compared to aluminum/polyester tape. It is suitable for mobile applications.

Inner Covering (Bedding)

Cables incorporating an armour or Protection layer have an extruded bedding of polyvinyl chloride (PVC) or zero halogen material (LSFOH).

  • It could be also called inner sheath or inner jacket, which serves as a bedding under cable armouring or protection sheath to protect the laid up cores.
  • Inner sheath is over laid up of cores.
  • It gives circular shape of the cable and it also provides Bedding for the armouring.
  • Inner sheath is provided by extrusion of thermoplastic over the laid up of cores.
  • Inner sheath is provided by wrapping at thermoplastic tape.
  • All multi-core cables have either extruded PVC inner sheath or thermoplastic wrapped inner sheath, which is compatible with insulation material and removable without any damage to insulation.

Protection Sheath

Lead sheath and Aluminum Copolymer are designed to be used in any applications where the cables may be subjected to solvent penetration or corrosive attack or hydrocarbons.

  • Lead Alloy Sheath

It is applied between two other sheaths and is the best protection against aggressive chemicals. This is an expensive solution, increases weight and bending radius. It presents poor vibration resistance and normally an armour is required to protect it from crushing.

  • ALC (Aluminum Copolymer)

It is an alternative to Lead Sheath and is composed by a longitudinal overlapped aluminum copolymer coated tape bonded to HDPE jacket and additional special alloy of polyamide/polypropylene sheath.

  • Excellent protection against corrosion and humidity.
  • Excellent impact resistance that in some cases prevents the use of the armour

This protection has a lower weight compared to lead sheath, cables have a smaller diameter, with a reduction of costs.

ALPE is the right choice to protect the environment. 

Separation Sheath (Bedding)

Cables incorporating an armour and Protection layer have an extruded bedding of polyvinyl chloride (PVC) or zero halogen material (LSFOH).

  • It could be also called Separation Sheath, which serves as a bedding between armour and protection sheath.
  • It also provides Bedding for the armouring.
  • Separation Sheath is provided by extrusion of thermoplastic over the protection sheath

Armour

Metallic armour are used when cables have to be installed direct buried, or if mechanical protection is required.

Following points must be considered:

  • Required tensile load
  • Expected pressure on cable during service
  • Protection against rodent
  • Protection against accidental damage
  • Minimum required bending radius.

SWA: Single Galvanized Steel Wire Armour, with diameters according to relevant standards, coverage min. 90%. This armour assures a very good mechanical protection and tensile strength. An additional counterspiral tape increases solidity, if required.

STA: Double Galvanized Steel Tape Armour, composed by two tapes with overlapped edge; thickness of each tape: 0.20 – 0.30 – 0.40 mm, according to cable diameter. It grants a coverage > 100%. Very good crush resistance, but fair tensile strength.

Brass tape of minimum thickness 0.075 mm can be used for special applications.

SWB: Galvanized Steel Wire Braid Armour, diameter of wire: 0.20 – 0.25 – 0.30 – 0.40 mm, with coverage of > 80%. It assures a good mechanical resistance, allowing a lower bending radius compared to other armour. It is preferable when there is movement or vibration.

For special application is possible to use stainless steel, tinned copper or special alloy wires.

Outer Sheath

Many compounds can be used as internal/external protection of cables. Working condition need to be considered for the right choice.

PVC, PE and LSFOH are the most popular materials, but we have to consider that different grades are available to meet specific working conditions.

Anyway the following conditions have to be evaluated:

  • Type of installation (indoor/outdoor, direct buried…)
  • Possible presence of humidity, oil, chemicals…
  • Behavior in case of a fire (fire propagation, fire resistance, emission of gases and smoke…)
  • Range of temperature
  • UV resistance in case of sun exposure

To optimize the behavior in case of fire, the sheath is made of LSFOH (Lows Smoke Zero Halogen) materials since, thanks to that, fire is not propagated, toxic or corrosive gases are not developed and a minimum quantity of white fumes are emitted.

Other materials can obviously be used in case of specific installation requirements, such as:

PVC, for example, where a higher resistance to oils and chemicals is required (but this material contains halogens, so it emits acid gas and smoke).

PE, when a higher resistance to water and moisture is required (this material is no anti-flame, though).

 

Applicable Standards

  • Basic Design: BS EN 50228-7
  • Conductor: IEC 60228
  • Flame Retardant: IEC 60332-1
  • Fire Resistant: IEC 60331
  • Acid Gas Emission: IEC 60754-1
  • Smoke Density: IEC 61034-2
  • Halogen Free: IEC 60754-1 (LSFOH)