Technical

Workers in our industry are required to undertake work to set standards of workmanship and quality to meet reliable, functional and safety aspects.  Most of these matters are addressed in a raft of Australian and international standards.  Some of these technical aspects are referenced and/or summarised in this chapter.

Construction and demolition wiring

Health and Safety Regulations specifically call up AS/NZS3012  Electrical installations – construction and demolition sites as a mandatory standard.  Electrical work carried out on electrical installations and electrical equipment used on construction and demolition sites must also be carried out in accordance with AS/NZS3000 – Wiring rules, except as varied by AS3012 and where additional controls apply.  Key requirements are summarised below:

Temporary construction wiring should be separated and readily distinguishable from permanent wiring (using iridescent yellow tape at max 5m spacing and marked ‘CONSTRUCTION WIRING’), and adequately protected from potential mechanical damage.

Switchboards must be to AS3000, of robust construction, IP23, with doors (that are lockable, not removable and means of holding open), with cut-out bottom plate to allow safe entry of leads with door closed, insulated tie bar for anchoring flexible leads and appropriately labelled (refer AS2013).  The location should be readily accessible and protected from damage and where there is more than one switchboard/distribution-board they must be distinguishable and the supply source identified.

Each switchboard/distribution-board must have one marked isolating switch that interrupts supply to all sub-circuits and sub-mains, including any socket outlets mounted on the board.  The main isolating switches must be lockable and marked as ‘MAIN SWITCH’.  The corresponding isolating switch on the distribution board must also be lockable and marked as ‘DISTRIBUTION BOARD ISOLATING SWITCH’.

Extension leads must be heavy duty sheaved, with no less than 1mm2 in cross-sectional area and fitted with appropriate plugs and sockets.  The maximum length is based on 5% voltage drop at 230Vac and rated current:

Residual Current Devices (RCD) 

All final sub-circuits of construction wiring must be protected at the switchboard where the sub-circuits originate by an RCD, with a maximum rated residual current of 30mA, that operates in all live (active and neutral) conductors.

All appliances, luminaires and other electrical equipment must be supplied from an RCD protected circuit that is fixed at the switchboard or incorporated into the socket-outlet or a portable socket-outlet assembly.  An exception is cranes, lifts, etc., where safe mechanical operation is at risk.

Socket-outlets must be rated not less than 10A and individually controlled by a double-pole switch.

Portable socket-outlet assembly (PSOA) must comply with AS/NZS3190 (Class H), overload and RCD protected and with heavy duty flexible lead not longer than 2m.  The PSOA can and should be used to provide protection on conventional outlets such as at a residential property.

Auxiliary socket outlet panel (ASOP) of appropriate robust construction, with lead tie bar, secured 1.2m to 2m above floor level and supplied with 4mm2 cord/cable (without plug and socket), from an RCD protected circuit at the switchboard or distribution board.  Domestic type power boards, double adaptors, etc. are not allowed.

Lighting should be mechanically protected, typically 40 lux for walkways and 160 lux for general area.  Where there is more than one lighting circuit spread lights between RCDs.

Emergency lighting should be sufficient to allow safe entry and exit from the site and capable of running for one hour and installed to the required lux levels as per AS/NZS3012 Electrical installations on construction sites and demolition sites.

Festoon lighting must be connected to ELV power supply (i.e. <50Vac) and suspended >2.5m above floor or directly below the ceiling.

Refer to AS3012 for other requirements including for generators and inverters, lift shafts and transportable structures.

Construction wiring – inspection, testing and record keeping

All construction wiring including switchboards, transportable structures and fixed equipment must be inspected and tested to AS/NZ3000 following initial installation and 6 monthly by a licensed electrical worker – electrician, with test methods detailed in AS3017.

Portable electrical equipment should be tested to AS/NZS3760 by a licensed electrician or a person RTO trained in the use of RCD Testers and Portable Appliance Testers (PAT).  After the testing is completed the test results are to be recorded with the following information:

• the name of the person who carried out the testing
• the date of the testing
• the outcome of the testing, and
• the date on which the next testing must be carried out.

The record may be in the form of a tag attached to the electrical equipment or other forms.

Electrical apprentices may do the work of an electrician subject to the normal training and supervision requirements.

Hire equipment must be tested prior to hire and then in accordance with the testing intervals listed below (refer to Table 3 of AS3012):

Power tools and leads

Electrical equipment connected to a socket outlet and used in hostile operating environments (e.g. construction), medical environments or amusement devices and hire equipment requires inspection and test.

A hostile or high risk operating environment is where it is likely to result in damage to the equipment or a reduction in its expected life span.  This includes conditions that involve exposing the electrical equipment to moisture, heat, vibration, mechanical damage, corrosive chemicals or dust.  It also includes equipment that is hand held or is moved during operation, such as hair dryers and vacuum cleaners.

The socket outlet for these devices needs to be protected by an RCD, also known as an Earth Leakage Protection Device or Safety Switch.

Electrical equipment used in lower-risk operating environments does not require inspection and testing or ‘tagging’.

Licenced electricians, or electrical apprentices (where permitted under the supervision of a licenced electrician and subject to appropriate training), are qualified to make repairs to and tests of electrical equipment.  Other persons can undertake visual inspection and use a Portable Appliance Tester (PAT) subject to being trained and certified by a Registered Training Organisation (RTO) for that PAT.

Extension leads should be connected to the nearest electrical power point, not over-extended, and not be over a specified length, generally 30 metres – based on 5% voltage drop at rated current – refer to AS3199 for details.

Extension leads, as far as is practicable, must be kept clear of the floor or ground and kept dry.  Leads should be supported at a height of about 2.4 metres to allow clear access of equipment beneath them, using insulated hooks or stands.  Do not wrap leads around scaffolds or steel structures.

Three-Pin Plugs and Sockets on flexible extension cords and portable power tools must be either a non-rewireable (moulded) or a transparent type and should be the shrouded type.  Do not use cables normally used for fixed wiring as extension cords.

Polarity:  Ensure that fittings for flexible conductors and flexible extension cords are wired identically and that the identity of active, neutral and earth connections are preserved in a like manner.

HRC fuses

Bridging blown HRC (High Rupture Capacity) fuse cartridges with bare or insulated wire is PROHIBITED.  Extensive damage can result from this so-called temporary repair and injury is a distinct possibility.  Blown HRC fuse cartridges must be replaced by serviceable HRC cartridges of appropriate ratings.

Identifying and elimination of ignition sources

Ignition sources can be any energy source that has the potential to ignite a fuel.  They can be categorised into three broad types: flames, sparks and heat. Some common examples of ignition sources are:

Table 2: Common examples of ignition sources

Some electrical equipment may also be a source of ignition.  However, not all electrical equipment is an ignition source if it is specifically designed so that it does not create sparks.  This type of equipment is referred to as “intrinsically safe” or Dust-excluding ignition proof (DIP).

You must identify any ignition source in your workplace that has the potential to ignite a flammable or combustible material.  You should also consider sources of ignition that are adjacent to your workplace or may periodically come into your workplace, for example vehicles (with hot engine and exhaust systems) making deliveries, visitors or other portable items like cordless power tools, radios and fans.

Eliminating ignition sources

When working on or near exposed energised electrical conductors take protective action, such as electrical isolation or shielding to prevent possible inadvertent contact with conductive objects.

Ignition sources must be eliminated from any hazardous areas:

• ensure electrical equipment in these areas is installed and maintained to the relevant Australian or International Standards.
• ensure electrical equipment is properly earthed
• implement administrative controls such as permit systems preventing hot work (for example, welding and cutting) in these areas.

Hazardous area classifications

The likelihood of the hazard being present in flammable concentrations will vary from place to place.  A location very close to an open source of hazard will have a high likelihood of a flammable atmosphere.  On the other hand, a switch housing and cable glands rated to IP65 say, the likelihood of ignition of a flammable atmosphere is much lower since it will only occur if the seal is broken.  Rather than work with an infinite range of possibilities, three zones are defined for each of Gases/Vapours and Dusts.

The presence of dust layers does not automatically lead to the dust zone.  The likelihood of the dust layer being disturbed to create a cloud needs to be considered.  Dust layers also need careful consideration in terms of ignition temperature.  Because the dust layer can make the equipment under it hotter than normal, a factor of safety is applied to the layer ignition temperature.

IP (Ingress Protection) Rating for equipment and enclosures

Ingress Protection (IP) Ratings are a system for classifying degrees of protection provided by enclosures, principally for electrical/electronic equipment (AS60529).  In general, the higher the IP rating, the more expensive the enclosure, but specifying a higher degree of protection does not necessarily ensure it is the most suitable for a particular application.

This information focuses on enclosures of electrical equipment with a rated voltage not exceeding 1000V ac and 1500V dc, but IP ratings can also apply to high voltage equipment.

The degrees of protection are classified in three general categories:

1) Protection of persons against access to hazardous parts inside enclosures.

This covers the protection of persons against accidental contact with electrically ‘live’ or otherwise hazardous mechanical parts contained within the enclosure, e.g. rotating blades, switch mechanisms etc.

2) Protection of the equipment inside the enclosure against the ingress of solid foreign objects.

This covers the protection of the equipment mounted inside the enclosure against tools, and/or strands of wire and/or the harmful ingress of dust particles.  Barriers, shapes of openings or any other means – whether attached to the enclosure or formed by the enclosed equipment – suitable to prevent or limit the penetration of the specified test probes are considered as a part of the enclosure, except when they can be removed without the use of a key or tool.

3) Protection of the equipment inside the enclosure against harmful ingress of water.

This covers the protection of equipment from water dripping, spraying, splashing and hosing or total immersion.  It should be noted that the specified degrees of protection in this third area do not include a strict classification for weather resistance, corrosion prevention, or resistance to other physically hazardous conditions, eg intrinsically safe.

The degrees of protection provided by an enclosure are indicated by the IP rating in the following way:

RATING LETTERS

The letter ‘X’ is used in place of the first or second numeral by equipment manufacturers to indicate that tests are not applicable to the product.  It is also used in standards to indicate that for the range of products covered such protection is not required.

The specified/claimed IP Rating applies when the equipment/enclosure is properly installed, according to the manufacturers’ instructions.  Where an enclosure needs to be machined or adapted for the attachment of cable glands, conduit or any other equipment, any instructions provided by the enclosure manufacturer should be strictly observed to ensure the required degree of protection is maintained.

In areas where only skilled (2) and/or instructed persons (3) have access, an enclosure with a lower protection category may be acceptable, whereas the opposite would apply where uninstructed persons have access.

FIRST Numeral – Protection against ingress of solid foreign objects

SECOND Numeral – Protection against harmful ingress of water

The minimum recommended aperture sizes to allow for drainage (eg condensation) and overcome the surface tension of water are 5.0mm diameter, or a 3.0mm width slot of 20.0mm2 area.

EX Ratings of Motors and electrical equipment

SELECTION OF APPARATUS (GASES)

SELECTION OF APPARATUS (DUSTS)