5. TECHNICAL CONSIDERATIONS
5.3 Residual Current Devices
5.3.1 The Wiring Rules (since July 2009) require RCDs to be installed for all electrical circuits, including among other things, circuits, socket-outlets, lighting points and hand-held equipment.35 Before 2007, RCDs were required to be installed, but for a narrower range
of circuits and installations. Many, including fixed or stationary cooking appliances such as ranges, ovens or hot plates and fridges and freezers did not require RCD protection.36
5.3.2 They are not to be the sole means of basic protection, but augment others such as use of increased insulation cover or protection by barriers, obstacles and placing electrical installations out of reach.37
5.3.3 A particular feature of RCDs is that they are capable of interrupting the full load current in a circuit when the earth leakage (residual) current reaches a predetermined value and trips the RCD. The Wiring Rules make provision for this, and the applicable load current rating value that can be interrupted by the RCD is, presently, not less than the greater of: 5.3.3.1 the maximum demand of the portion of the electrical installation being
protected by the device;
5.3.3.2 the highest current rating of any overload protective device on the portion of the electrical installation being protected.38
5.3.4 RCDs monitor the difference between the flow of electricity going out to a load or appliance (that is, the active wire current) and that coming back from the load (that is, the neutral wire return current) in the circuit. If that difference (the residual current or earth leakage current) reaches the predetermined trip setting value of the RCD, it means that, somewhere in the circuit, current is leaking to earth and there may be a risk of shock. This may be because an electrical appliance is faulty due to a circuit being installed incorrectly, or as a result of a damaged wire, e.g. one penetrated by a staple.
35 Australia/New Zealand Standard 3000:2007 Electrical installations (known as the Australia/New Zealand Wiring Rules), clauses 1.5.6.3 and 2.6.3.2.1.
36 See, for example, Australia/New Zealand Standard 3000:2000 Electrical installations (known as the Australia/ New Zealand Wiring Rules), clause 2.5.3 (required only for final subcircuits in domestic electrical installations for socket-outlets and lighting); Australia Standard 3000:1991 Electrical installations—Buildings, Structures and Premises (known as the SAA Wiring Rules), clause 0.5.74.
37 Australia/New Zealand Standard 3000:2007 Electrical installations (known as the Australia/New Zealand Wiring Rules), clauses 1.5.6 and 2.6.1.
38 Australia/New Zealand Standard 3000:2007 Electrical installations (known as the Australia/New Zealand Wiring Rules), clause 2.6.2.
5.3.5 RCDs are one means by which the risk of electrocution is minimised, and to a very low level. They do not control the voltage, but instead the time for which the current is permitted to flow. Some RCDs (Class I) will trip and interrupt the circuit when the residual current exceeds 10 milliamps and it will interrupt the circuit current within 40 milliseconds. Others (Class II RCDs) will trip with a residual current of greater than 30 milliamps and will interrupt the circuit within 40 milliseconds. Class II, 30 mA RCDs, are the standard type for use in domestic circuits.
5.3.6 The time for which the human body is exposed to a current is important because time is one of the two critical factors at issue: the longer the time of current flow in the body the more likely it is that respiratory paralysis will occur, and that there will be an effect on the heart, burns suffered and cardiac arrest occur.
5.3.7 The other critical factor is current: the higher the current, the smaller the time for which the body can be exposed to it before injury and death might result. Also relevant, but unnecessary to cover here, is the path which the current might take through the body. So too are factors such as what part of the body makes contact with the circuit, or whether contact is made with wet or dry skin.
5.3.8 The particular risk which the evidence before me has shown to exist is the use of metal staples and foil. Obviously, the penetration of a cable with a metal staple, combined with the use of foil had the real potential to cause electric shock or electrocution because both conduct electricity. Plastic staples do not conduct electricity, thus minimising the risk of electrocution. Some risk remains however with the use of plastic staples because the staple may have the effect of completing a circuit by bringing the insulation in contact with a defective live cable.39
5.3.9 In summary therefore, the range of electrical risks might be classified as threefold for present purposes:
5.3.9.1 exposure, in roof voids, to poor or aged wiring or indeed (as occurred in the case of Mr Rueben Barnes), electrical faults;
5.3.9.2 exposure, in those voids, to wiring which had lower resistance to disturbance or interference than in habitable areas of the home;
5.3.9.3 the use of foil and metal staples, both being capable of conducting electricity and the second being capable of penetrating the coating (insulation and sheathing) on electrical cables.
5.4 Fire
5.4.1 The risk of fire is one which, in an immediate sense, is a risk of damage to property but is necessarily one which also involves a real threat of personal injury and perhaps death. 5.4.2 My Terms of Reference direct particular attention to damage to property claimed to have
arisen from the HIP, which includes fires.
5.4.3 No evidence before the Commission suggested that there had been any loss of life as a result of a fire caused by insulation installed under the HIP. There were, however, many fires and some resulted in property damage and in some very few cases, the entire loss of the home. In many of the cases however, the loss was far less extensive.
5.4.4 Fire risk emerges in a number of ways. One important way is by the overheating of lamps, luminaires and electrical appliances (such as exhaust fans) in ceilings. The overheating results because air, which would otherwise be circulating around such installations, is unable to escape because insulation has been installed too close.
5.4.5 Both the Wiring Rules and AS 3999-1992 deal specifically with such matters. Both impose minimum clearances between lamps, luminaires (including downlights), appliances and the installation of insulation to ensure adequate airflow so as to avoid the risk of fire.
5.4.6 AS 3999-1992 provides (in clause 2.6.1):
The flow of electric current in cables generates heat which is dissipated to the surroundings. The introduction of thermal insulation around cables will reduce the heat dissipation and in some instances may result in electrical cables overheating and the electrical insulation exceeding its rated temperature, and degrading. It is also possible that electrical equipment may overheat if enclosed by thermal insulation.40
5.4.7 Section 4.12 of the 1991 Wiring Rules provided:
Thermal insulating materials shall be separated by not less than 25mm from any lamps or luminaires and shall not prevent free air flow around or through the luminaire. Where the thermal insulation is of the loose fill type, barriers shall be provided to maintain the 25mm separation.41
5.4.8 The 2007 Wiring Rules state on this topic:
4.5.2 Lamps and luminaires …
Lamps, luminaires and their associated ancillary gear shall be so installed as not to cause undue temperature rise, ignition or deterioration of the materials- (a) on which they are mounted; or
(b) that they illuminate. …
Recessed luminaires and their auxiliary equipment shall be installed in such a manner that necessary cooling air movement through or around the luminaire is not impaired by thermal insulation or other material.
Where thermal insulation is of a type that is not fixed in position, eg loose fill, a barrier or guard constructed of fire-resistant material shall be provided and secured in position to maintain the necessary clearance (see Figure 4.7). …
Where thermal insulation may reasonably be expected to be installed in the space containing a recessed luminaire, the luminaire shall be installed in such a manner as to provide for the subsequent installation of thermal insulation.42
40 Australian Standard 3999-1992 Thermal Insulation of Dwelling—Bulk Insulation—Insulation Requirements, clause 2.6.1.
41 Australian Standard 3000-1991 Electrical installations—Buildings, structures and premises, clause 4.12. 42 Australian/New Zealand Standard 3000:2007 Electrical installations (known as the Australian/New Zealand
5.4.9 Figure 4.7 states that there must be a clearance of 50mm between thermal insulation and an incandescent lamp and 200mm between thermal insulation and a halogen lamp.43
5.4.10 The problem with which both sets of rules seek to deal is insulation being installed without respecting safe clearances between things which generate heat (appliances, lights etc) and a product (ie insulation) that would serve to prevent that heat escaping as it ought. The Wiring Rules, because they apply to work performed by electricians, focus on electrical installations whereas AS 3999-1992 approaches the issue from the perspective of the insulation installer.
5.4.11 Beyond this risk, there is always the inherent electrical risk of arcing caused by defective appliances or lights, or by loose connections. However, risks of this kind were not identified to the Commission as being in any material respect a matter of interest. 5.4.12 Another real risk of fire is in the installation of lamps and and downlights themselves.
Although contrary to the Wiring Rules, in some cases, lights are, on occasion, installed in ceilings in too close a proximity to combustible material such as wooden beams.44 So, for
example, an untrained person might install a downlight without regard to the location of the beam above and in doing so bring that heat producing appliance in very close contact with timber. This, however, is not a problem which is connected itself with the installation of insulation, but another one of the pre-existing problems which might have manifested itself in the course of the HIP’s implementation.