AC -v- DC Fuses

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An electrical fuse is simply a short length of copper/silver wire enclosed in a suitable ceramic tube, yes? Well in some cases yes but generally no!

Did you know that the design of electrical fuses differ when a fuse is used within an alternating current (AC) system such as a domestic electrical system and a direct current (DC) system which ultilise batteries or DC generator as energy sources such as electric train/traction systems.

Why? Well in AC systems fault current interruption is aided by the inherent ‘zero crossing’ point of the alternating current supply. In other words as the voltage supply reverses polarity, the fault current will also reverse, thus the internal physical process of fuse element disintegration are aided such that fault current conduction could and in most cases only last for a part of one cycle of the AC supply, i.e. 20 milli-seconds (50Hz supply) or 16.67 milli-seconds (60 Hz supply).

Conversely, in DC systems, there is no polarity reversal of the supply, hence the internal physical process of fuse element disintegration is unaided. Consequently, features are designed into the fuse element to aid and enhance element disintegration quickly and efficiently to minimise ‘let through energy, i.e. energy conveyed during the fuse disruption process.

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About the author:

Eur Ing Dr Robert Brown (Robert) is the Executive Director of Fraser George and Associates Limited and is a Consultant and Forensic Engineer in the fields Electrical Electronic and Control Engineering.

Robert is an accomplished professional Electrical Expert Witness having prepared and presented many court compliant reports and presented oral evidence within the High Court, Crown Courts and County Courts.

Robert is a registered Chartered Electrical Engineer, specialising in the fields are control engineering, parameter data capture and accurate data ‘representation’. Robert graduated from Sheffield Hallam University with a first class honours degree in Electronic Systems and Control Engineering and followed this by completing doctorate research in Electrical Engineering, again at Sheffield Hallam University where Robert undertook research studies in the field of Disintegration and Arcing in Electrical Fuses. Robert is now considered to be a leading world expert in the field of electrical circuit protection systems, the phenomena of electrical fuse operation and the attributes of clearing ‘fault’ electrical current circumstances. Robert has published my pure and applied research studies in peer-refereed journals and at conference.

In his spare time Robert is a Formula 1 motor racing enthusiast and enjoys outdoor activities especially hill walking and scrambling, golf and fishing. Robert is a brass band enthusiast, a tuba player and band manager of Hatfield and Askern Colliery Band. When time allows Robert also enjoys travelling and reading any books associated with travel and popular science.


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