Fire-resistant cable line: cable, fasteners and penetration as a single system

What a Fire-Resistant Cable Line Is

A fire-resistant cable line (FRCL) is not a cable marked FR, but a set of structural elements that together ensure the preservation of the operability of an electrical circuit during a fire for a specified time. The fire resistance of a cable line is determined not by a single material, but by the assembly as a whole: the type of barrier, the type of cables, the method of fastening and the filling of openings. That is why fire resistance is a verifiable property that applies to the entire line, not to its individual elements.

The requirements for the design of lines of fire protection systems are determined by regulatory documents. In the Republic of Kazakhstan, the requirements for the fire resistance of connecting and supply lines connected to fire protection systems are established by building norms SN RK 2.02-02-2023. The fire resistance of lines must be ensured by laying fire-resistant wires and cables. However, the cable itself is only one of the elements of the system. A fire-resistant cable penetration through walls and floors must have a fire resistance limit not lower than the fire resistance limit of the crossed structure.

What Elements the System Consists Of

A fire-resistant cable line includes several interrelated elements. Each of them performs its own function, and the failure of any of them leads to the loss of operability of the entire line.

Why Choosing Only an FR Cable Is Not Enough

A cable marked FR has passed tests for maintaining operability in a flame. However, these tests are carried out under controlled conditions that do not reproduce a real cable route. Under real fire conditions, additional factors act on the cable: mechanical loads from collapsing structures, thermal expansion, vibration. If the fasteners do not maintain operability, the cable falls, and the circuit breaks regardless of the fire resistance of the cable itself.

A fire-resistant cable line must maintain operability as a single system. This means that not only the cable, but also the fasteners, penetrations and connections are subjected to testing. The fire resistance of a cable penetration is determined by the assembly as a whole: the type of barrier, the type of cables and the filling of the opening. An error at any stage of installation can lead to the loss of fire resistance of the entire system.

The Role of Fasteners and Supporting Structures

Fasteners hold the cable on the route. During a fire, metal structures heat up, lose strength and deform. If the fasteners are not designed for exposure to high temperatures, they fail, and the cable loses support. Fire-resistant cable lines are installed using special fastening products that maintain operability during a fire.

Requirements for fasteners are established by the installation regulations of specific FRCL systems. There must be at least three fastening points per metre of cable line length. When fastening to a concrete surface, dowel clamps are used; when fastening to plasterboard, special dowels for plasterboard sheets are used. It is prohibited to fasten FRCL wiring to surfaces whose fire resistance is lower than the required operability time of the line.

If the cable line passes through a fire-resistant box, the maximum distance from the box to the cable fastening must not exceed 200 mm. This prevents sagging and displacement of the cable when heated.

The Role of Cable Penetrations

A cable penetration is a structural element designed to seal the places where cables pass through enclosing structures with standardised fire resistance limits. The penetration prevents the spread of combustion into adjacent rooms for a standardised time. The fire resistance of a cable line cannot be higher than the fire resistance of the penetration through which it passes.

Requirements for penetrations are established by GOST R 53310-2009. Cable penetrations, sealed entries and busbar passages made in enclosing structures with standardised fire resistance limits or fire barriers must have a fire resistance limit not lower than the fire resistance limit of the crossed structure. If a wall has a fire resistance limit of EI 90, the penetration must also have a fire resistance limit of at least EI 90. Otherwise, the fire will spread through the opening, and the fire resistance of the entire line will be determined by the weakest element.

For laying cables through fire barriers, certified fire-resistant cable penetrations are used. Installation of penetrations is carried out in accordance with the manufacturer’s technical regulations. Independent modification of the composition of the penetration or replacement of materials is not permitted.

How to Ensure the Required Operability

The logic of ensuring the fire resistance of a cable line is built from the required operability time to the selection of all elements of the system.

1. Determine the required operability time. For fire protection systems, this time is determined by the project. According to SP 6.13130.2021, for warning and evacuation control systems, fire-resistant cable lines with an operability time of 60 minutes or less are used, if calculated by the designer. In Kazakhstan, the requirement for the fire resistance of connecting and supply lines is established by SN RK 2.02-02-2023.
2. Choose a fire-resistant cable. The cable must have an FR marking and a corresponding certificate. Tests are carried out according to GOST IEC 60331-1-2021 for cables with an outer diameter of more than 20 mm and according to GOST IEC 60331-2-2021 for cables of smaller diameter. Test method: exposure to a flame with a temperature of at least 830 °C simultaneously with mechanical impact.
3. Use a certified fastening system. Fasteners must comply with the installation regulations for the selected FRCL system. The number of fastening points is at least three per metre of line. Fastening to surfaces with insufficient fire resistance is not permitted.
4. Install fire-resistant penetrations. Penetrations must have a fire resistance limit not lower than the fire resistance limit of the crossed structure. For each barrier, a penetration certified for that type of structure is used.
5. Make connections in fire-resistant boxes. All connections and branches of cables are made only in fire-resistant junction boxes. For explosion hazard zones, explosion-proof junction boxes complying with GOST IEC 60079-14 are used.
6. Confirm the fire resistance of the entire line. The fire resistance of a cable line is confirmed by tests according to GOST R 53316-2021. This standard establishes the procedure for testing under a standard fire temperature regime and applies to wiring subject to requirements for maintaining operability.

Laying of fire-resistant cables is carried out in accordance with the installation rules. More details on the requirements for the route and fastening — in the material laying of fire-resistant cables. Fire-resistant cable penetrations must be certified and installed in accordance with the manufacturer’s regulations: fire-resistant cable penetration.

Typical Design and Installation Mistakes

Choosing an FR cable without taking into account the other elements of the system. The cable has passed the tests, but the fasteners are not designed for high temperatures. During a fire, the fasteners fail, the cable falls, and the circuit breaks. The fire resistance of the cable does not save the line if the fastening system does not work.

Using ordinary fastening products for FRCL. Standard dowel clamps and staples do not maintain operability during a fire. For FRCL, special fastening elements that have been tested as part of the system are used.

Absence of fire-resistant penetrations at places where barriers are crossed. The cable laid is fire-resistant, but there is no certified penetration at the point of passage through the wall. Fire spreads through the gap, and the barrier loses its properties.

Connections outside fire-resistant boxes. Branch boxes do not have the required fire resistance limit. During a fire, the connection fails, and the line loses operability.

Fastening FRCL to surfaces with insufficient fire resistance. If the surface to which the cable is fastened has a fire resistance limit lower than the required operability time of the line, the fastening loses its load-bearing capacity before the standardised time expires. Fastening FRCL to such surfaces is prohibited.

Ignoring the manufacturer’s requirements during installation. Each FRCL system has an installation regulation. Independently changing the fastening design, replacing elements or reducing the number of fastening points leads to the loss of certified properties.

FAQ

How does a fire-resistant cable line differ from a fire-resistant cable?

A fire-resistant cable is a cable product that has passed tests for maintaining operability in a flame. A fire-resistant cable line is a system including the cable, fasteners, penetrations, connections and the method of installation. The operability of the line during a fire depends on all elements, not only on the cable.

Which documents confirm the fire resistance of a cable line?

The fire resistance of a cable line is confirmed by tests according to GOST R 53316-2021. Cables are tested according to GOST IEC 60331-1-2021 and GOST IEC 60331-2-2021. Penetrations are tested according to GOST R 53310-2009. For a specific FRCL system, the manufacturer provides the technical installation regulations and a certificate of conformity.

Can ordinary fastening products be used for a fire-resistant line?

No. Fasteners must maintain operability during a fire for the time corresponding to the required fire resistance of the line. Ordinary dowels and staples lose their load-bearing capacity when heated. For FRCL, special fastening elements that have been tested as part of the system are used.

What should the fire resistance limit of a cable penetration be?

The fire resistance limit of the penetration must not be lower than the fire resistance limit of the crossed structure. If a wall has a fire resistance limit of EI 90, the penetration must also have a fire resistance limit of at least EI 90. Requirements for penetrations are established by GOST R 53310-2009.

How many fastening points are required per metre of a fire-resistant line?

There must be at least three fastening points per metre of cable line length. This requirement is contained in the installation regulations of FRCL systems and is confirmed by tests.

What to do if a fire-resistant line passes through several fire barriers?

For each barrier, a fire-resistant penetration is installed with a fire resistance limit not lower than the fire resistance limit of that barrier. The type of penetration is selected depending on the material of the barrier and the required fire resistance limit. Specific solutions are adopted according to the regulations of the penetration manufacturer.

Sources

• GOST IEC 60331-1-2021 “Tests for electric cables under fire conditions. Circuit integrity. Part 1. Test method for cables of rated voltage up to and including 0.6/1.0 kV and with an overall diameter exceeding 20 mm under flame with a temperature of at least 830 °C simultaneously with mechanical shock” — in force, introduced 01.01.2022 — protect.gost.ru
• GOST IEC 60331-2-2021 “Tests for electric cables under fire conditions. Circuit integrity. Part 2. Test method for cables of rated voltage up to and including 0.6/1.0 kV and with an overall diameter not exceeding 20 mm under flame with a temperature of at least 830 °C simultaneously with mechanical shock” — in force — protect.gost.ru
• GOST R 53316-2021 “Electrical wiring. Preservation of operability under the standard fire temperature regime. Test methods” — in force, introduced 01.01.2022 — protect.gost.ru
• GOST R 53310-2009 “Cable penetrations, sealed entries and busbar passages. Fire safety requirements. Fire resistance test methods” — in force, introduced 01.05.2009 — protect.gost.ru
• SN RK 2.02-02-2023 “Fire safety of buildings and structures” — in force — adilet.zan.kz
• SP 6.13130.2021 “Fire protection systems. Low-voltage electrical installations. Fire safety requirements” — in force — docs.cntd.ru
• Technical regulations for the installation of FRCL systems — in force — manufacturer’s technical documentation, spetskabel.ru
• Technical regulations for the installation of fire-resistant cable penetrations — in force — manufacturer’s technical documentation, dkc.ru