The 18th Edition wiring regulations require designers and installers to ensure that their installations are designed and constructed so that the risk of ignition from high temperatures or electric arc is minimised. Protection requirements include protecting against fire caused by insulation, arcs, sparks and high temperatures. Installing arc fault protection is recognised in the 18th edition of the wiring regulations as a means of mitigating the risk from fire in final AC circuits due to arc faults.
Arc Fault Protection & Arc Fault Detection Devices
Arc Fault Detection Devices (AFDD) have been proven to reduce the number of incidents of electrical fires in countries where these devices are used. AFDDs detect and automatically disconnect arc faults that occur in damaged or crushed cables, in loose terminations, and in ageing installations where the insulation quality degrades over time.
Arc faults cause overheating and the temperatures that are generated from such overheating can be high enough to ignite flammable materials and cause fires. AFDDs monitor the condition of a circuit for unusual conditions that are indicative of a series or parallel arc. These arc fault conditions can occur in electrical installation circuits and in cords and leads and in equipment / appliances connected to those circuits. AFDDs detect arc fault conditions & automatically disconnect the power to the circuit with an arc fault. With the government statistics revealing so many fires involving electrical distribution and appliances the use of AFDDs on final A.C. circuits would address some of these issues, including those associated with cords & leads.
MCBs & RCDs
Although the wiring regulations permit the use of RCDs as a measure for protection against insulation faults, and require the use of other circuit protection devices such as MCBs to provide protection against short circuit and over-current conditions, those devices cannot detect or disconnect arc faults. Neither of those devices are capable of detecting serial arc faults, and parallel arc faults will go unnoticed due to the fact that the magnitude of an arc fault is insufficient to operate an RCD or MCB.
Types of Arc Fault
Serial arcing faults: These are typically caused by a loose connection or a damaged conductor. In this arc fault condition current flow is always lower than the operational load current. Miniature Circuit Breakers and Residual Current protective devices will not detect these electrical faults.
Parallel arcing faults between conductors: These are caused by electric arcs resulting from damage to the insulation that permits minimum contact between the two live conductors. MCBs or RCBOs may trip if the fault current is high enough. However AFDDs are extremely sensitive and will disconnect parallel arcing faults from 2.5A
Parallel arcing faults between phase or neutral/protective conductor: AFDDs will detect arcing faults against the protective conductor and provide adequate fire protection where no RCD is used. However Wylex AFDDs are combined with 30mA Miniature RCBOs that reliably detect and shut down this type of parallel arc fault. AFDD with Miniature RCBO provides the highest levels of protection for the installation and its users.
For more content on 18th Edition arc fault devices, visit Electrium’s dedicated 18th Edition webpage or download the Wylex guide to Arc Fault Detection.