Engineering:High Resistance Connection

A high-resistance connection (HRC) is a hazard that results from loose or poor connections in traditional electrical accessories and switchgear which can cause heat to develop, capable of starting a fire. Safety devices such as fuses and residual-current devices (RCDs) are unable to detect thermal rise and disconnect the electrical supply because they cannot sense a HRC. A safety device to prevent HRCs operates by effectively monitoring for the abnormal thermal rise and will prevent ignition, smoke or burning odour of the electrical accessory or electrical installation. An example extract from the National Union of Teachers (NUT) Fire Safety Brief:

• Electrical equipment should be regularly maintained by competent people. Machines should not be allowed to overheat. Care should be taken not to cover machines while they are switched on as this is particularly likely to cause overheating. Trailing cables should be regularly checked for damage. Loose or poor connections in traditional electrical accessories and switchgear can cause heat to develop capable of starting a fire. This problem is known as High Resistance Connection (HRC) and safety devices such as fuses and Residual Circuit Devices (RCDs) are unable to disconnect the electrical supply because they cannot sense HRC. Consideration should be given to the installation of a preventative system designed to stop electrical connections and accessories from reaching a temperature which would result in a fire. Such a device operates by effectively closing a switch at a pre-set temperature to prevent ignition, smoke or burning odour.

Thermal monitoring of the connection and providing an HRC device close to the probable location where a fault may develop is key to providing early warning or isolation to reduce the risk of fire.