Series arc faults are normally considered the most problematic because they have potential to cause ignition but are not reliably detected NEED HUMIDITY CONTROL? Condair offers the UKs widest range of both humidifiers and dehumidifiers, provided with expert application knowledge and system design. standard uses in the verification of AFDD products. Using specially conditioned cable samples, I confirmed that, in most cases, AFDDs could detect series arc faults sufficiently quickly to avoid an ignition. AFDDs were also proven to be more effective at detecting series arc faults than circuit breakers with residual current detection for example, residual current breakers with over-current (RCBOs). However, RCBOs were also successful in some cases. While I confirmed the lower threshold of AFDD sensitivity (2.5Amps), I found that arc faults of around 1Amp were not detected. Secondary research also confirms that arc faults of 1.7Amps, and possibly lower, are viable sources of ignition. While exploring different electrode types, it was noted that where the breakdown voltage was significantly reduced by using carbon rods, the AFDDs detection of arc faults became unreliable. So, it can be said that AFDDs work reasonably well at identifying arc faults that accord with the fault conditions assumed by the product standard, but they do not prevent all ignitions caused by arc faults. Will AFDDs reduce the number of electrical fires? Fire statistics, such as those published by the Home Office, are not sufficiently granular to show any influence from arc faults, and it appears there is little evidence to support AFDDs having much effect on fire statistics. As pointed out earlier, an AFDD will not prevent all ignitions caused by arc faults. Consequently, it is my view that they are not likely to be effective in reducing the incidence of electrical fires. So, what now? Humidifiers Dehumidifiers Design Manufacture Supply Install Commissioning Service Spares Contact us for free expert advice Tel: +44 (0)1903 850 200 Email: uk.sales@condair.com Web: www.condair.co.uk Humidity Control and Evaporative Cooling Clearly, electrical fires remain a concern worthy of our focus. The spectrum of causation to electrical fires is broad, and includes equipment connected to an installations fixed wiring system. So, for a strategy to reduce the incidence of electrical fires, it should focus on regular inspection and testing, such that as much as possible faults are identified before they evolve into fires. Making such verification work mandatory for all installations in the built environment would be a reasonable measure to reduce the incidence of electrical fires. Legislation requiring this regular verification already exists, including Electrical safety standards in the private rented sector (England) Regulations 2020, so its scope could be broadened to include private rented, social housing and owner-occupied housing. CJ KENELM HOARE MCIBSE is a senior associate at Hoare Lea 32 October 2021 www.cibsejournal.com CIBSE Oct21 pp30-32 Arc Fault Detection.indd 32 24/09/2021 14:20