Wiz. You need to read the report throughout.
High resistance faults cause localised heating due to many things. The common ones are poor connections and overload.
The poor connections are usually caused by poor installation or faulty manufacture. The overload is usually caused by poor selection of components or simply too much current being drawn through the connection.
the cables etc at the mains intake position of the electrical distribution system of a building (where most current will be carried)
should be designed to carry the designed load without overheating .
This means the components need to be correctly rated for the job they are intended for. The rating also makes the assumption there is no heat insulation around the wiring and components and they are able to cool by dissipation of the heat created by normal use. Insulation could be simply the cables have been covered by "building insulation" materials, or the adjacent storage of combustibles.
I'd be more inclined to believe that many fires involving electrical equipment are caused by the additional heating effect of poor electrical connections causing 'electrical arcing'.
Not all poor connections manifest themselves immediately as arcing. It is more common (in my experience) for a high resistance fault to be caused first. Many people assume a high resistance fault needs a load to be applied to the circuit to cause the fault. This fails to realise the electrical insulation of the circuitry or components can fail for very many reasons causing what was an insulator to become a semi conductor and thereby create a circuit with its own load caused by (and causing) the heating effect. Connection corrosion, insulation heating leading to smoulder, surface tracking, in line arcing etc are all feasibilities. As the insulation breaks down it can cause cross conductor arcing. But this is usually a symptom of the fire and not actually the cause. The cause is the heating of the insulation or surrounding combustibles to auto ignition temperature by the localised high resistance heating. As Mark says.
High resistance heating and arcing is also different between AC and DC electricity ( vast over simplification) as well and there is a lot of high voltage DC in many buildings now, with alternative energy generation. Something I am looking at.
Sorry this post is a bit vague and rambling but it is a big subject and this is only a discussion forum and not a text book
In reply to John's post. I have investigated a number of fires in modern electrical components and they are by no means "fire safer" than old ones. Faulty new components will ignite as will poorly installed new ones. And yes I agree timber (or other combustible) mounting boards are a problem.
