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Exploding the common AFDD myths Since being introduced to the IET Wiring Regulations in 2018, AFDDs have been the subject of much debate. Unfortunately, these discussions have also led to some misunderstanding about the technology, so our Associate Member is here to shatter five frequent misconceptions
DAVID ENEFER
Product Manager, Circuit Protection Systems
MYTH NO.1: AFDDS AREN’T REALLY REQUIRED Regulation 421.1.7 of BS 7671:2018 +A2:2022 now states that AFDDs conforming to BS EN 62606 SHALL be provided for single phase AC final circuits serving socket outlets not exceeding 32A in: • Higher risk residential buildings (HRRB) • Houses in multiple occupation (HMO) • Purpose-built student accommodation • Care homes. For all other premises, the use of AFDDs conforming to BS EN 62606 is recommended for single phase AC final circuits supplying socket outlets not exceeding 32A. Amendment 2 also provides further guidance, on the terms ‘shall’ and
“AFDDS DETECT AND DISCONNECT ARC FAULTS ON RING CIRCUITS, RADIAL CIRCUITS, SPURS AND LEADS, WHATEVER THE MODE OF CONNECTION” 38 cabletalk DECEMBER 2022/JANUARY 2023
‘recommended’ to help users understand the verbal forms used within BS 7671. ‘Shall’ is a requirement, ‘recommended’ means should. This clarification was necessary because the term ‘recommended’ in BS 7671 was either misunderstood or not being taken seriously by some organisations. MYTH NO.2: AFDDS WON’T WORK ON RING CIRCUITS I wish I had a fiver for every time I’ve heard this. It’s simply not true! AFDDs detect and disconnect arc faults on ring circuits, radial circuits, spurs and leads, whatever the mode of connection. Even if a ring becomes broken it becomes two radial circuits – and as we know, AFDDs work on radial circuits! The confusion may have come from the belief that arc faults can’t occur on a ring circuit because a broken ring is two radials and there is no potential difference at the break in the ring. This means that there can be no arc fault
at that precise point, but it doesn’t mean that arc faults can’t occur at other points on that same circuit. Ring or radial, AFDDs will detect arc faults wherever they can occur in such final circuits. MYTH NO.3: AFDDS ARE SUSCEPTIBLE TO NUISANCE TRIPPING Once again, this is simply not the case. The microprocessor in an AFDD is looking for a specific arc fault signature on the wave form and uses a sophisticated algorithm. In addition, the product standard, BS EN 62606, includes a range of tests to ensure AFDDs won’t respond to expected conventional