Circuit Magazine, Master Electricians Technical Story
How many times have you entered a ceiling cavity and noticed wiring laying across ceiling trusses unprotected with a blatant disregard for electrical safety and the Wiring Rules standard?
Ceiling spaces are environments where there is an increased risk of an electric shock from contact with damaged or exposed live wiring.
The latest version of the Wiring Rules (AS/NZS 3000:2018) was released in June 2018 and contained improved clarification from the previous version with an added explanation addressing mechanical protection for cables and prohibiting RCD protection being used solely in lieu of mechanical protection for wiring systems that are likely to be disturbed. This is identified in clause 3.9.3.3.2
Ceiling spaces are a common area where wiring systems become disturbed due to the reduced space to move about, coupled with the ease and frequency of people accessing these areas. Many trades including electricians, builders, plumbers, roofers, insulation installers as well as homeowners, access these spaces for a multitude of reasons so it’s imperative that all electric cabling is adequately protected.
Due to the increased risks posed by mechanically unprotected cable in these environments, in 2018 the West Australian government passed legislation making it illegal to enter a ceiling space in a domestic installation with the power still on. We believe other states may follow this initiative.
Electrical Safety Office inspectors in Queensland are proactively auditing new and existing ceiling space wiring installations, to ensure compliance with the Wiring Rules. Previous audits have identified non-compliant wiring practices which could have proven to be a dangerous electrical hazard if left uncorrected.
Wiring Rules Requirements
AS/NZS 3000:2018 clauses 3.3.2.6, 3.9.3.3.1 and 3.9.3.3.2 address roof space wiring requirements to prevent damage to cables and electrical equipment. Damage frequently occurs from persons standing and/or laying on cables or kicking them as they move around in reduced access areas.
Traditional approaches to support cables have been to run cables along trusses and bearers held in place with pin clips to prevent undue sagging and movement and cut timber blocks/strips to protect cable where they pass across beams, joists and trusses. These approaches can lead to longer cable runs, increasing material costs, volt drop and installation time. In some cases, electricians have resorted to using PVC conduit for protection, which whilst effective, can increase installation time and material costs. Costs and time are reasons electricians offer for running cables unprotected or unsupported, however these are not acceptable reasons for breaching legislation and standards or creating dangerous installations for the occupier and those whom follow you into the roof space.
Clause 3.9.3.3 Wiring systems likely to be disturbed defines the environment where consideration for additional mechanical protection for cables and appliances is required. This applies to ceiling spaces.
Clause 3.9.3.3.2 then specifies 3 fundamental mandatory requirements to be assessed when cables are installed in these environments. Cable support, fixing/securing wiring connections to appliances and mechanical protection. To meet the general mechanical protection requirement referred to in clause 3.3.2.6, it refers the reader to use Appendix H of AS/NZS 3000 ‘WS Classification of Wiring Systems’. Wiring systems comprise the cable, busway, support, fixing and enclosure elements and are classified for their ability to;
- (a) Maintain circuit integrity under fire conditions for a specified period; and,
- (b) Maintain circuit integrity against mechanical damage of specified severity.
Similar in structure to the IP Code (i.e; IP56), the WS system is made up of two letters designating the WS system and two numbers, the first digit relating to the fire conditions and the second to mechanical damage. For the purpose of this article we will ignore the first digit as it doesn’t relate to mechanical protection of cables.
Appendix H, clause H5.2 gives guidance to the acceptable methods to achieve a minimum degree of a mechanical barrier from damage likely by a person entering a ceiling space. The examples given are simple and cost effective.
Conclusion
As an industry, we need to reacquaint ourselves with the AS/NZS 3000 requirements for ceiling space installation of wiring and review the current methods used. It may be identified that we have not met compliance in this specific area and thus need to reassess how we can rectify this.
Note
To help the industry find an easy way to ensure ceiling compliance, the market will often see a business opportunity and develop new products that could fill this void. One such product has been recently developed specifically to provide fixing securement and mechanical protection, it’s called Harry’s Hat. No doubt other products will emerge over time as electrical workers realise current practices are not working.
Written by Master Electricians Australia for Circuit Magazine November 2019 Edition.
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