Active thermal monitoring preventing fires in electrical installations

In 2011 the London Fire Brigade Fire Investigation Team identified an increase in the number and the severity of consumer unit fires. The cause was identified as High Resistance Connection due to loose connections and also non-compliant miniature circuit breakers which could fail catastrophically and were subject to a manufacturer product recall.

There was also evidence that a fire once started within a Consumer Unit was not contained and was putting people’s lives at risk as they are generally located on escape routes, under the stairs or by the main entrance to a property.

Thermarestor is a product whose sole function is to detect abnormally high temperatures in electrical installations and prevent fire. It provides additional safety which isn't available from any currently available and installed device protecting our electrical installations in our homes and work places.

Examples of the safety devices currently installed within electrical installations are listed below together with a brief description of operation. 

Miniature Circuit Breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits.

Residual Current Circuit Breaker 

A Residual-Current Circuit Breaker (RCCB) is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energised conductor and the return neutral conductor. Such an imbalance may indicate current leakage through the body of a person who is grounded and accidentally touching the energised part of the circuit. A lethal shock can result from these conditions. RCCBs are designed to disconnect quickly enough to prevent injury caused by such shocks. They are not intended to provide protection against over current (overload) or short-circuit conditions

Residual Current Circuit Breaker with Over current Protection (RCBO)

The Residual Current Circuit Breaker with Over current Protection (RCBO) is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance may indicate current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A lethal shock can result from these conditions. RCBOs are designed to disconnect quickly enough to prevent injury caused by such shocks and they are intended to provide protection against over current (overload) or short-circuit conditions.

Fuse

A fuse is a type of low resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source circuit. It’s essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected. Short circuit, overloading, mismatched loads or device failure are the prime reasons for excessive current.

Thermarestor detects the resulting abnormal heat generated within an electrical installation connection point. This includes heat produced by High Resistance Connections, overload, incorrectly rated cables and manufacturing defects.

There are many examples around the UK where a fire had started due to HRC. One example is a National Trust property, Clandon Park House. This property was destroyed by fire on 29th April 2015 and was later found to have started within an electrical distribution board. The cost of this fire is going to run into the millions of ï¿¡'s and could have been prevented by using thermal monitoring such as Thermarestor. Unfortunately, this phenomenon is not only confined to electrical installations in the UK, it is a worldwide problem which needs to be addressed.

Surrey Fire Service - Report of Fire at Clandon Park House

There has been recent research carried out by the Electrical Safety First (ESF) and the London Fire Brigade into the flammability of plastic consumer units which has highlighted the need for change in the protection of these enclosures. A change has now been made to BS 7671 (Wiring Regulations) which requires non-combustible e.g. metal Consumer units to be installed in dwellings from 1 January 2016. The change is not retrospective and therefore it is unlikely that existing installations will be upgraded to accommodate these changes.

Thermarestor can prevent Consumer units, Distribution boards, electrical appliances and accessories from being exposed to the HRC risk and any unwanted abnormal development of heat, therefore preventing an electrical fault generating heat which could cause a fire. This is achieved before there are any signs of smoke or flame to enable maintenance to be carried out and to determine the cause of the abnormal temperature. Thermarestor will also prevent the power supply to the faulty circuit from being energised until the fault is repaired and the Thermarestor unit replaced.

Thermarestor uses a single point detection method within the electrical equipment being monitored. This allows a specially designed component to be positioned in close proximity to a connection providing very early detection of excessive heat. Once activated, the supply can be isolated to prevent a fire. If isolation is not required, the component can provide a simple open to closed connection which could be introduced to building management and fire alarm systems, security systems and other types of local alarms.

Electrical accessories i.e. single/double socket, fused spur and shower pull cord switch can also be protected with Thermarestor utilising the already installed Residual Current Device (RCD) within a consumer unit or distribution board to isolate the whole circuit containing the faulty accessory should a fault occur. Thermarestor will prevent the generation of high temperatures within a socket that could be caused by overload or faulty wiring. 

The installation of the electrical accessories with this technology incorporated will be no different from standard fittings; however, there will be a need to ensure an RCD is fitted and tested.

The setting up of the protection within a consumer unit or distribution board can be carried out quickly, there may be a need to install further devices that respond to an activation, depending on what actions need to be carried out i.e isolation or notification.

The inclusion of active thermal detection and monitoring technology would prevent the possibility of fires starting within an electrical installation and as a result remove a risk of ignition. Saving lives and property.