Electrical fires continue to be a significant issue in UK #installations. Electricity is a major cause of accidental fires in UK homes with over 17,000 electrical fires each year. Fire statistics for 2017/18 identify that almost 23 % of domestic #electricalfires are caused by faulty appliances and leads.
The 2017/18 fire statistics also attribute 12 % of fires to electrical distribution (wiring, cabling, plugs). These statistics demonstrate that electrical fires occur and can cause #injuries, and #deaths and #damage or #destroy significant amounts of property. Electrical fires can be a silent killer occurring in areas of the home that are hidden from view and early detection.
Household #electricity supplies are fitted with #fuses or #circuit-breakers to protect against the effects of ‘overcurrents’ (‘overloads’ in circuits which are electrically sound and ‘short-circuit faults’ due to contact between live conductors in a #fault situation.) RCDs provide additional #protection against the effects of earth leakage faults which could present a fire risk.
Electricity is the major cause of accidental fires in UK homes - over 20.000 eletrical fires each year.
Protective Measures as A Function of External Influences
It is widely accepted that #RCDs can reduce the likelihood of fires associated with earth faults in electrical systems, equipment and components by limiting the magnitude and duration of current flow.
The ability to provide additional protection against the risk of fire is recognised in #BS7671, for example:
For protection against the risk of fire, the RCD is required to disconnect all live conductors i.e. line and neutral.
Regulation 422 defines the precautions to be taken in ‘Installations where Particular Risks of Danger of Fire Exist’. Regulation 422.3.9 requires, in #TN and #TT systems, that wiring systems, with the exception of mineral insulated #cable and #busbar trunking systems, are protected against insulation faults to earth by an RCD having a rated #trippingcurrent not exceeding 300 mA.
Section 705 defines the particular requirements that apply to ‘Agricultural and Horticultural Premises’. Regulation 705.422.7 requires, for the protection against fire, an RCD having a rated tripping current not exceeding 300 mA.
Research commissioned by the Department of Trade and Industry in 1997, established that a common source of #earthfaults is surface tracking on insulation. The report confirms that currents as low as 50 100 mA have been found to be sufficient to cause ignition and fire as a result of tracking and that at these currents, an RCD rated to provide protection against electric shock would also have prevented ignition. Attention is drawn also to the fact that minimising the presence of electrically conducting dust or liquids, which may arise due to #leakage or #spillage, can reduce the onset of surface tracking.
Again, in BS 7671, Chapter 42 sets requirements to prevent the wiring systems and electrical equipment from being exposed to the harmful build-up of materials such as dust or fibre likely to present a fire hazard.
It is clear that increased use of correctly selected RCDs, in addition to good wiring practice, can reduce the effects of electric shock and the possibility of fire risk significantly. RCD protection also provides an additional level of protection where the wiring complies with Bs 7671 but the integrity of the #wiringsystem has been damaged.
Types of Installation Risks
Mechanical damage to cables. The #risk of people cutting through live cables is well known. Examples include the following:
Penetration of cable insulation in walls and beneath floorboards. This is a common occurrence during DIY work in the home. The main danger arises when someone comes into contact with live cables either directly or indirectly, resulting in an electric shock.
Cutting the supply lead or an extension lead with an electric lawn mower or hedge trimmer. This is another common occurrence and can result in either a serious electric shock or death when bodily contact is made with the exposed live conductor.
Trapped or poorly maintained extension leads. The effects here are similar to those described above.
Vermin. It is surprisingly common for mice and other vermin to chew through cables, exposing the live conductors.
In all the above situations, even if bodily contact does not occur, damage to the cable insulation can result in a fire risk which is significantly higher if RCD protection is not used.
Locations containing a bath or shower. These locations present a much higher risk because a wet body presents a much easier path for an electric current to flow to earth. Consequently, BS 7671 prohibits the use of electrical equipment, other than shavers connected through an appropriate shaver supply unit, within 3 m of the bath or shower basin. Nevertheless, tragedies have occurred as a result of people using extension cables to supply portable electrical appliances in these locations.
Fire risk associated with fixed electrical appliances. Faulty electrical appliances increase the risk of fire. For example, fire can occur when the insulation on an electric motor breaks down due to deterioration or external damage. This can result in the ignition of any flammable material, including dust, in the vicinity of the non-insulated ‘live’ parts.
Bad wiring practice. Although all new and/or modified installations must comply with the current edition of BS 7671 it is possible that a person may incorrectly erect or subsequently incorrectly modify an installation.
Faulty electrical appliances increase the risk of fire!
Examples of the risks of #electricshock and fire resulting from incorrectly wired systems include the following:
Inadequate earthing or bonding
Wires trapped during installation
Insulation damaged during or after installation
Bad system design
RCDs are not a substitute for good wiring practice. However, correctly installed RCDs will continue to provide a high degree of protection against the risks of #electrocution and fire even when an installation deteriorates due to poor #maintenance or lack of compliance with BS 7671.