Electrical Connection Technical Information
Electrical Connection Fires
Each year there are many incidents, recorded by Fire & Rescue Services, of fires in homes and businesses caused by high contact resistance /high-temperature electrical connections. Categorising these incidents has highlighted that this risk is especially common in electrical supply intake equipment (main intake fuse, electricity meter & consumer unit connections).
If a high resistance/temperature electrical connection begins to develop, it may steadily get worse without anyone becoming aware of it. High resistance electrical connections can be initiated by simple local environment changes i.e. through temperature fluctuations (including cyclic heating from electrical loading) or vibration and even if the connection cables have been moved or disturbed slightly. They can also be caused by sub-standard installation or maintenance works. A high resistance/temperature electrical connection can take weeks, months or even years to develop. Eventually, the connection may become hot enough to ignite the insulating materials around it, or eject sparks through electrical arcing to ignite combustibles in the vicinity. The ensuing fire can then spread destroying property, life and business.
Developing high resistance/temperature electrical connections cannot be easily detected, without the use of specialist equipment. It is therefore easy to understand how, once developed, they can deteriorate and cause fire.
The Stages of Electrical Connection Ignition
Heat develops in the electrical connection.
Electrical connection contact force reduces slightly causing a higher resistance connection.
Increased heat develops within the electrical connection.
If the temperature rises above 90°C copper contact surfaces oxidise more rapidly and the connection resistance increases generating more heat.
If the copper creep temperature limit is achieved (135°C) the connection contact force can decrease due to changes in copper elasticity/plasticity. This again increases connection resistance and generated heat (the creep temperature limit for brass is even lower at 91°C).
Connection resistance & heat increases until eventual ignition of local insulation materials or electrical arcing ejects sparks which ignite local combustibles.
Brief Glossary of Terms
Copper / Connection Elasticity
Material Creep
Connection Resistance
Connection resistance is related to the surface contact, contact force and the elasticity of the copper. If the contact force is reduced, the connection resistance rises and so does the heat developed in the connection.
Copper Creep Temperature Limit
Copper creep can be a problem within an electrical connector as it has the potential to reduce internal contact force (tightness) and therefore increase contact resistance.