Under the 18th edition cables have to be fixed in place using metal clips and supports that have a melting point high enough to withstand the heat of a fire. Materials such as plastic and aluminium are therefore no longer acceptable as a sole form of support.

I need a definitive melting point figure for fire clips  that meets the 18th edition I havent a copy of the 18th but im told Chapter 52 of the Wiring Regulations is the area where it might say Can anyone offer advice

Thanks 

Edited by user 14 April 2021 06:27:28(UTC)  | Reason: couple of words missing

it would be new installs and yes i guess the manufacturer must supply the specification.

Thankyou the 18th doesnt spell it out but again its not for the electrical legislation peeps to do this although it woukd have been helpful

Thankyou alan

You will not find a definitive survivability temperature for such fixings.  It does not exist.

The requirement is not that the clips survive a fire.

The requirement is that they do not suffer from premature collapse.

Don’t ask what is defined as a premature collapse because that is not defined anywhere either.

For me, this isn’t a function for the H&S department.  The selection of components to form the electrical installation is down to your electrical design engineer to specify.  If you are doing it, you also need to be taking design responsibility for the installation by signing the EIC’s relevant part.

That aside, there is no temperature rating for the components required.

It is down to the engineering judgement of the designer how they comply with clause 521.10.202.

“521.10.202       Wiring systems shall be supported such that they will not be liable to premature collapse in the event of a fire.

NOTE 1: Wiring systems hanging across access or egress routes may hinder evacuation and firefighting activities.

NOTE 2: Cables installed in or on steel cable containment systems are deemed to meet the requirements of this regulation.

NOTE 3: This regulation precludes, for example, the use of non-metallic cable clips or cable ties as the sole means of support where cables are clipped direct to exposed surfaces or suspended under cable tray, and the use of non-metallic cable trunking as the sole means of support of the cables therein.

NOTE 4: Suitably spaced steel or copper clips, saddles or ties are examples that will meet the requirements of this regulation.”

If you take Note 4, bearing in mind, this is a note to the clause, not part of the clause’s requirement; it suggests that copper might be a suitable material.

Pure copper has a melting point of around 1085 Deg. Celsius, steel is higher.  Note, however, that steel is an alloy, and copper is often alloyed.  Variation in the composition of the alloys will result in varying melting points for the different materials.  Also, it is not the melting point that is important. The point at which the clip’s structural strength is no longer adequate to support the cable is critical for preventing premature collapse.

The “strength” required of the support will depend on the configuration of the installation, clip spacings, cable sizes & cable composition.

After considering the "strength", the “weakening” of the support will depend on the way the fire behaves, the substrate etc.