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Confused by the new wiring system installation requirements?

Since their release in June 2018, the new Wiring Rules have sparked a lot of discussion throughout the electrical industry. The new requirements for the installation of wiring systems (cables) and the different methods of protection, have been at the centre of many debates.

 At a recent information night, a NECA member, who is often involved in the installation of wiring systems (cables) below raised floors in data centres and other similar installations, expressed serious concerns about the impact of the new requirements on his work. The standard imposes a range of new requirements on the installation of wiring systems (cables) that are likely to be disturbed or damaged.

I thought it may be a good time to give a more detailed explanation and provide a simplified view of the new requirements for the installation of Wiring Systems (cables).

 What is a Wiring System?

 A wiring system can be defined as a group of one or more conductors, cables or busbars along with all parts that are used to secure them in position. It also includes any mechanical protection that is provided for the conductor. The first concept that we need to understand is that the method of installation will determine the classification of the wiring system. It will be either a “Wiring system likely to be disturbed” or a wiring system requiring “protection against mechanical damage”.

 Protection against mechanical damage

Wiring Systems requiring protection against mechanical damage are generally cables installed in hollow walls, walls with plasterboard or similar material on either side of the wall studs.

When wiring systems (cables) are installed in locations where they may reasonably be expected to be subjected to mechanical damage, you are required to provide adequate protection. This can be done by one or any combination of the following:

(a) Mechanical characteristics of the wiring system

(b) Location selected

(c) Provision of additional local or general mechanical protection

If additional mechanical protection is selected, appendix H of AS/NZS 3000:2018 provides an explanation of the WS classification system and practical information about what is needed to comply with each classification. Now ‘What is a WS classification?’ you may ask, well it has been around for some time and comes from another Australian Standard specifying fire and mechanical protection ratings for wiring systems.

There are some specific methods of installing wiring systems where the Wiring Rules provide additional guidance or requirements, such as;

Wiring systems near building surfaces

– Wiring systems that are fixed in position by fasteners, or held in position by thermal insulation, or by passing through an opening in a structural member concealed within 50 mm from the surface of a wall, floor, ceiling or roof.

Exception: This requirement need not apply to wiring systems that can move freely to a point not less than 50 mm from the surface in the event of a nail or screw penetrating the cavity at the location of the wiring system.

Wiring systems near roofing material

– wiring systems passing through a structural member, or are fixed in position, within 50 mm from the face of the supporting member to which the lining or roofing material is attached.

Protection methods for wiring systems requiring protection against mechanical damage

Where protection of a wiring system is required, the wiring system must be protected by an RCD with a maximum rated operating residual current of 30 mA. Alternatively, it can be provided with an earthed metallic armouring, screen, covering or enclosure that allows a short circuit protective device to operate under fault conditions. The other possibility is to provide adequate mechanical protection at a minimum of WSX3 to prevent damage.

The most common protection method e used by our industry, particularly for circuits up to 32A and in domestic installations, is the installation of an RCD. This method is difficult to apply to consumer mains and submains. One of the other methods of protection will be required unless you protect the submain with a Type “S” RCD which are expensive and not readily available.

The other forms of protection can be harder to achieve, especially in existing homes where alterations are being carried out. New homes aren’t as difficult.

You may use a metallic armouring, screen, covering or enclosure. These must be earthed, if less than 2mm in thickness, so that the short circuit protective device will operate under fault conditions. You may elect to use steel conduit that is earthed, or anaconda earthed with an appropriate earth clip as recommended by the manufacturer. Steel sheeting suitable earthed if less than 2mm thick, across the studs can also be used.

An option that will be infrequently used, is providing adequate mechanical protection at a minimum of WSX3 to prevent damage.

WSX3 is a substantial rating and requires the wiring system (cables) to be provided with medium-duty protection against damage, meeting the requirements of the appropriate tests of AS/NZS 3013.

Any wiring system (cables) with additional 2.0 mm sheet steel coverage with a maximum unsupported width of 100 mm.

Or you may use any WSX2 systems with an additional 1.6 mm sheet steel coverage and unsupported width not exceeding 100 mm.

Another option is to use galvanized medium tube complying with AS 1074 or very heavy-duty conduits complying with AS/NZS 2053 or AS/NZS 61386.

Mind blowing stuff, however there may be a need to use this option especially in medical installations, consumer mains or submains.

A Quick reminder for wiring systems installed vertically

Where wiring systems are installed vertically, they must be installed in a way that avoids damage to any part of the wiring system. You must take care to ensure that damage isn’t caused by the wiring system’s own weight or by the support or fixings used to secure it. This can be achieved by providing additional supports for cables enclosed in a vertically installed wiring enclosure. Cable supports need to be provided at intervals not exceeding 8 m or according to the cable manufacturer’s recommendations. Remember, cables installed vertically also need to comply with the requirements for wiring systems requiring protection against mechanical damage.

Wiring systems likely to be disturbed

Now that we have explored the requirements for wiring systems requiring protection against mechanical damage, let’s take a look at the requirements for wiring systems likely to be disturbed.

Neither the installing electrician nor the Electrical Inspector gets to decide which wiring systems are likely to be disturbed, this is predetermined by the standard. Systems deemed ‘likely to be disturbed’ are as follows:

(a) On the surface of a wall or on the underside of a ceiling or roof

(b) In a space between a floor and the ground to which a person may gain entry

(c) In parts of a ceiling space where access is greater than 0.6 m in height

(d) Within 2.0 m of any access to any space to which a person may gain entry

(e) Below raised floors

Wiring systems (cables) installed in positions where they are likely to be disturbed, shall be supported at suitable intervals to prevent undue sagging and accidental withdrawal of cables from electrical equipment exposing single insulated conductors.

The wiring systems shall be selected and installed using one or a combination of the following methods to minimize the risk of mechanical damage:

(a) Mechanical characteristics of the wiring system

(b) Location selected

(c) Provision of additional local or general mechanical protection

The big change here is that RCDs can’t be used in lieu of mechanical protection for wiring systems that are likely to be disturbed.

Need more information?

• Electrical installations – “Wiring Rules” – AS/NZS 3000:2018

• NECA Technical Knowledge Base

• Call Roy Sands on 1300300031

2 comments to this Blog

Roy Sands, 6:56 AM. Tuesday 2019 23rd April

Clause 2.6.3.2.5 Alterations to electrical installations requires that socket outlets to an existing circuit shall be protected by an RCD where required by the Wiring Rules, the RCD protection need only to be fitted at the commencement of the additional wiring.

Anonymous, 8:28 PM. Tuesday 2019 19th March

What to do when installing a new socket outlet in addition to an old wiring system where you run it of an existing socket outlet ?

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