BASEC News

Vermin and Cables

18/05/09
BASEC receives a significant number of enquiries about the effect of vermin and related threats to cables. Installers and end users are often frustrated by repeated attacks on cables by mice, rats, squirrels, pigeons and even termites. Choosing the right cable for the situation, or finding permanent, preventive solutions can appear difficult and frustrating.

Mice, rats and squirrels are the most common pests attacking cables in the UK.  They gnaw cables not particularly for food but as nesting material.  Cables commonly affected are those under floorboards, in outbuildings, and in ducts.  Most types of cable can be affected, including power distribution, final circuit installation, data and fibre.

Controlling the pests is a good way to prevent further problems – seek advice from a specialist firm – but be aware that some pests are protected species.  The presence of a cat can deter many vermin.  Other tricks to deter vermin include using steel wool to block holes and voids, but mice especially can gain entrance through very tiny holes.

It is possible to include deterrent additives into the sheathing of cables, but these have limited effect with more aggressive vermin such as mice or rats and hence they are mainly used overseas where termite damage is the main problem.

Cables gnawed through by vermin can result in electrical short circuits and fires, which are significant threats to life and safety.  Consequently, the IEE Wiring Regulations sets specific requirements for the assessment of “External Influences” such as fauna (coded as AL) in Section 522.  The normal condition (AL1) is with no vermin present.  Where aggressive fauna are experienced or expected (AL2), an appropriate choice of wiring system or special protective measures must be used, such as cable with better mechanical protection, by using more appropriate routing or locations for the cables, or by providing additional protection such as conduit.

Regular insulated or sheathed cable such as PVC conduit wire or flat twin and earth have no mechanical protection against gnawing.  Steel wire armoured cable can offer some protection (though the sheathing may be attacked); mineral insulated cable or steel conduit offer good protection.  Re-routing cable to avoid spaces where vermin live (such as under floors) can be effective, as is embedding in plaster, cement or concrete.

Further information and assistance is available at www.basec.org.uk, technical@basec.org.uk, or contact BASEC directly on 01908 267300

 

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