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  • robertbrown

AC -v- DC Fuses

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.

A helpful link, …

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 Expert Witness having prepared and presented many court compliant reports and presented oral evidence within the High Court, Crown Courts and County Courts.

For further information please contact Robert via;

Email,… or

Tel Land: +44 (0)1777 709175

Tel Mobile: +44 (0) 7976250624

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