Arc Fault Detection Devices
PROVIDING COMPLETE CIRCUIT PROTECTION
Recommended as a means of providing additional protection against fire
Regulation 421.1.7 of BS 7671 has been introduced recommending the installation of arc fault detection devices (AFDDs) to mitigate the risk of fire in AC final circuits of a fixed installation due to the effects of arc fault currents.
Accidental Domestic Fires UK total: Approximately 19,300 Accidental domestic fires of electrical origin
Accidental electrical Dwelling Fires Accidental electrical dwelling Fires: 14,186 (53.4% of all accidental dwelling fires) | Of which caused by faulty appliances and leads: 3667 (25.9% of electrical fires)
What is an Arc Fault?
An arc-fault occurs when loose or corroded connections make intermittent contact and causes sparking or arcing between the connections. This translates into heat, which will break down the insulations of the wire and potentially trigger an electrical fire. Such arc’s can range in power and vary a great deal in strength and duration.
Types of Arc Faults
Parallel arc faults are found with damage caused to insulation which allows current to flow between conductors, usually between phase and neutral.
Series arc faults are found in loose terminal connections, damaged cords or frayed/damaged conductors. These arc’s are created in one conductor only, either phase or neutral.
New Amendment 2 Changes
Arc fault detection devices SHALL BE used as a means of providing additional protection against fire
Regulation 421.1.7 has been redrafted requiring the use of arc fault detection devices (AFDDs) to mitigate the risk of fire in AC final circuits of a fixed installation due to the effects of arc fault currents.
Regulation 421.1.7 (Updated 2022)
AFDDs conforming to BS EN 62606 shall be provided for single-phase AC final circuits supplying socket-outlets with a rated current not exceeding 32A in:
- Higher Risk Residential Buildings (HRRB)
- House of Multiple Occupancy (HMO)
- Purpose-built student accommodation
- Care Homes
Note 1: HRRBs are assumed to be residential buildings over 18m in height or in excess of six storeys.
For all other premises, the use of AFDDs is recommended for single-phase AC final circuits supplying socket-outlets not exceeding 32A.
Where used, AFDDs shall be placed at the origin of the circuit to be protected.
What is an Arc Fault Detection Device (AFDD)?
Arc Fault Detection Devices use digital electronics to analyse the waveform of an A.C. circuit to detect arc faults.
The device continuously monitors the circuit for different variations including the duration of an arc and the waveform. Once the device detects an irregular fault the device trips and disconnects the circuit, reducing the chance of it over heating and potentially causing an electrical fire.
What is an AFR?
The Proteus AFR is an arc fault detection device combined with short circuit, overload and earth leakage detection.
Installer Guidance
If used, an AFDD/AFR shall be placed at the origin of the circuit. Examples of use: premises with sleeping accommodation; where there is risk of fire; combustible construction materials; fire propagating structures; locations with endangering of irreplaceable goods.
Potential Causes of an Arc Fault Could be?
Trapped/Damaged Cables
Loose Terminations
Cable Wear
Damage Caused by Construction Work
Detection Characteristics
When all three inputs are simultaneously sustained for at least 100mS, the AFDD will trip. This maximises arc fault detection whilst minimising the risk of nuisance tripping.
A sustainable current of a certain magnitude
A minimum number of consecutive half cycles of arcing conditions
Presence of Hi-Lo asymmetrical frequency components
Technical Information
Tripping Characteristics
