Frequently Asked Questions: Cables and fire protection

Can I use SY, YY and CY cables in an electrical installation?

YY, SY and CY cables are made to various manufacturers specifications but not governed by any National, European or International standard, hence these are not currently recognized in BS 7671:2018, Regulation 133.1.1 of BS 7671:2018 requires every item of equipment to comply with the appropriate British or Harmonised Standard.

Whilst Regulation 134.1.1 permits the use of new materials and inventions, it is providing that the resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations. But it’s difficult to see how a designer could provide such assurance in the absence of the appropriate standards.

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Do I have to install AFDDs?

A new requirement in BS 7671:2018 is Regulation 421.1.7 makes recommendations as opposed to requirements for Arc Fault Detection Devices (AFDD).

It is a good idea for the electrical designer to have thorough communication with the client to understand the use of the installation to make an informed decision and decide if the installation of AFDD’s would be beneficial.

Examples of where such devices can be used include:

  • premises with sleeping accommodation
  • locations with a risk of fire due to the nature of processed or stored materials, i.e. BE2 locations (e.g. barns woodworking shops, stores of combustible materials)
  • locations with combustible constructional materials, i.e. CA2 locations (e.g. wooden buildings)
  • fire propagating structures, i.e. CB2 locations
  • locations with endangering of irreplaceable goods.

This IET webinar on SPDs and AFDDs provides further guidance.

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Do cable supports above plasterboard ceiling need to be metal?

It’s important to understand why this particular Regulation was introduced. It’s to prevent wiring systems from hanging, which may hinder evacuation or obstruct firefighting activities.

Regulation 521.10.202 of BS 7671:2018, states that wiring systems shall be supported such that they will not be liable to premature collapse in the event of a fire.

The electrical designer could deem it appropriate to rely on the plasterboard ceiling to provide fire protection to the wiring system in order to prevent premature collapse. However, many influences should be considered such as building size, complexity and evacuation time.

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Where do I have to install LS0H cables?

The type of cable required for a project may be specified by the client, but in some cases, it won't be.

Regulation 422.2 of BS 7671:2018 sets out the requirements for conditions for evacuation in an emergency. it refers to the following conditions:

  • BD2: Low density occupation, difficult conditions of evacuation
  • BD3: High density occupation, easy conditions of evacuation
  • BD4: High density occupation, difficult conditions of evacuation.

Authorities such as those responsible for building construction, public gatherings, fire prevention, hospitals, etc. may specify which BD condition is applicable.

Regulation 422.2.1 states that cables shall not encroach on escape routes unless they meet the requirements of BS EN 60332-3 and BS EN 61034-2. These standards require cables to be tested to verify reduced fire propagation and low smoke emissions.

The Building Regulations for England 2010, 2019 edition, Volume 2: Buildings other than dwellings, Requirement B1, states that where necessary, escape routes are sufficiently protected from the effects of fire and smoke.

There are lots of acronyms for these types of cable and many are registered trademarks, examples below:

  • Low Smoke Zero Halogen (LS0H/LSZH)
  • Low Smoke Halogen Free (LSHF)
  • Halogen Free (HF)
  • Zero Halogen (ZH)
  • Low Smoke and Fume (LSF)
  • Zero Halogen Low Smoke (OHLS) and
  • Halogen Free Flame Retardant (HFFR).

LSF and LSZH cables are often confused to be the same, which is not the case. PVC compounds are used during the manufacture of LSF cables, and whilst additional additives reduce the smoke emissions, they are not eliminated, there are no standards governing LSF cables, unlike LSZH which are manufactured and tested to BS EN 61034 and BS EN 60754 series.

The BASEC website can provide further guidance.

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What are the requirements for cables to minimise the spread of fire?

To prevent the spread of fire between fire segregated compartments, cables shall be installed in accordance with Section 527 of BS 7671:2018. Cables are required to be flame retardant in accordance with BS EN 60332-1-2, or installed within containment having the necessary resistance to flame propagation, to the relevant standards identified in Regulation 527.1.5, typically metallic containment.

Wiring systems which do not meet these requirements, such as PVC, shall be completely enclosed in suitable non-combustible building materials.

It’s also important to note, that containment systems which pass through fire segregated compartments, shall be externally sealed, as required by Regulation 527.2.1, and internally sealed as required by Regulation 527.2.2 to the degree of fire resistance of the respective element before penetration.

This IET Wiring Matters article provides guidance on sealing of wiring system penetrations.

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Is fire stopping a requirement in BS 7671:2018?

Fire stopping is called sealing of wiring system penetrations in BS 7671:2018. It is covered in Section 527.2. It states that where containment for wiring systems passes through a fire-resisting element of the building, it shall be internally sealed to the equivalent degree of fire resistance (if any) of the element which has been penetrated.

However, it should be noted that fire stopping is a specialist job and the installer must be competent to carry out the works.

This IET Wiring Matters article provides guidance on sealing of wiring system penetrations.

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