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Safety equipment In the Home Office report, currents of


the order of 50 to 100mA were found to be sufficient enough to cause flame ignition as a result of tracking. At these currents, an RCD rated to provide protection against electric shock would have prevented flame ignition. The onset of surface tracking of insulation can be accelerated by the presence of electrically conducting liquids, which may arise because of leakage or spillage.


Under these conditions, an RCD can be


expected to operate and delay or reduce the risk of fire ignition, although the report goes on to say: ‘Neither RCDs nor over- current protection devices will prevent fire ignition under all fault conditions. However, RCDs when properly used in addition to over-current devices and thermal cut outs can protect against a wider range of fault conditions which cause fire.’ In order for an RCD to operate and isolate the supply (via a current imbalance), ignition would have already occurred. Resistive heating of connections can generate heat in excess of 1,000°C, well above the ignition point of many adjacent combustibles such as PVC cable insulation and plastic consumer unit enclosures.


The answer?


It is clear that although RCDs and overcurrent devices do have an important role to play in mitigating the risk of an electrical fire, they are not able to address the majority of fault scenarios that may subsequently initiate fire ignition. Until now, there had not been a practical or straightforward way of detecting overheating of connections, yet these are a major cause of electrical fires. As smart technology is now capable of


addressing this anomaly, routine installation of these relatively inexpensive devices could lead to a step change in fire safety. We believe it is the single most significant innovation in fire safety since the introduction of smoke alarms


John Newbury is product manager at Ramtech Electronics. For more information, view page 5


Reference


1. Consumer Safety Research – Residual Current Devices – added value for home safety, DTI, https://webarchive.nationalarchives.gov.uk/+/ http:/www.dti.gov.uk/homesafetynetwork/pdf/ rcd.pdf


FOCUS


www.frmjournal.com MAY 2019


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