Flame Retardant (FRT) Cables and Fire Resistant (FRS) Cables

  • Conductor

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

  • Insulation

                        MGT+XLPE/Silicon Rubber (SR)

  • Metallic Screen

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

  • Inner Covering (Bedding)

                        LSFOH (Low Smoke, Zero Halogen)

  • Protection Sheath

            Lead Alloy Sheath/ALPE Sheath (Aluminum Copolymer)

  • Separation Sheath (Bedding)

                        LSFOH (Low Smoke, Zero Halogen)

  • Armour

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

  • Outer Sheath

                        LSFOH (Low Smoke, Zero Halogen)

– Produces a wide range of specially designed, fire resistant Safety Cables. They are manufactured to resist fire alone, as well as a combination of fire and water, and fire combined with mechanical shocks.

– Our Safety Cables are used within public buildings, emergency systems such as fire alarm circuits, and emergency lighting systems. They are self-extinguishing and low smoke-emitting.

– Fires have a high cost in terms of loss of human life and damages to plants and structures.

– Fire is the major cause of destruction, but we must consider that one of the main causes of death are the inhalation of toxic gas that develop and the presence of dense smoke, interfering with the identification of escape routes.

– It has to be kept into consideration, then, that even the most sophisticated alarm systems or emergency systems can be useless if their performances are compromised by the destruction of the cables caused by the fire. This is the reason why, over the last few years, the companies have strongly invested in design and development of insulation materials and cables granting the best performances in case of fire, while reducing fumes and acid gases emission and granting the circuit integrity even in case of fire.

The behavior of cables concerning flame presence covers various aspects. A first feature is how the cable reacts in these circumstances. This brought us to consider two performances:

FLAME RETARDANT

FIRE RESISTANT

Flame retardant cables can resist the spread of fire, but due to fire the cable is fully destroyed and no circuit integrity is assured. All the systems connected to cables are completely out of work.

Flame retardant cables (FRT) are not intended to assure service during a fire but are chosen to prevent the flame spreading.

Fire resistant cables (FRS) maintain circuit integrity and continue to work in the presence of fire. It is important for fire alarm systems, emergency lighting, voice alarm systems…. In this case it Is possible to assure building evacuation, alarm signals, activation of extinguishing systems. Fire resistant cables are always as well Flame retardant as they assure the highest level of security during a fire.

GAS EMISSION / SMOKE DENSITY

Other features should be considered n this context. More precisely, these are the quality and the quantity of gas that are developed during the fire.

In fact, the cause of fire victims often doesn’t only consist in the presence of fire, but it’s also due to the gases that develop from the burning of materials.

One of the most popular material used for insulation and jacket for electrical cables is PVC.

This material can show excellent flame retardant properties, due to the presence of chlorine in the compound, that is a

flame suppressant. On the other hand, chlorine is a corrosive and toxic gas and it develops a heavy smoke. All of these characteristics have to be avoided in case of fire. This is why the following features have to be considered:

Absence of halogen (acid gas) in the cables Low emission of smoke

Specific tests, according to different standards, are therefore defined to verify this performance.

Conductors

For Safety cables conductors are Plain Annealed Copper, Tinned Copper or Aluminum.

Conductors can generally be according to IEC 60288:

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

 

Insulation

The most widespread technologies to guarantee the electric cables connection integrity during a fire is currently the following:

  • Ceramified Silicone Rubber
  • Mica Glass Tape and cross-linked polyolefin

The taping with mica tape is the most typical solution; it allows the use of several insulation materials since the fire resistance is guaranteed by the tape.

The silicone rubber is currently the most frequently used solution because it simplifies and speeds up the installation, thanks to the easy peeling and to the lack

of tape.

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.

Fire resistant cables generally can be laid-up in concentric construction and in pairs.

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

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:

Copper Wire Screen

The Copper screen on the underground cables are for following reasons: To relieve electrostatic stresses from the insulation of the core. To earth the leakage fault currents or the capacitive currents preventing damage to the insulation.

Copper Tape Screen

The copper screen is usually connected to the ground at the end terminations for shorter cable lengths. For longer cable lengths earthing can also be done at splices to provide redundancy.

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 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.

  • ALPE (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 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

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: IEC 60502-1, BS EN 50288-7
  • 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)