IT1 U17 - Protection - Complete

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CGLI 2330 Certificate in Electrotechnical Technology Level 2 Inst Tech: Unit 202 – Principles of Electrotechnology

Unit 17 – Protection

Protection Unit Aims By the end of the unit participants should be able to: List basic principles of shock protection, circuit overload and short-circuit protection Syllabus Reference: 2.3.07

Protection against Electric Shock (Chapter 41) The definition of „electric shock‟ is: “A dangerous physiological effect resulting from the passing of an electric through a human body or livestock” (from BS 7671 „Definitions‟). Chapter 41 (Protection against Electric Shock) of BS 7671 details the means of providing appropriate protection. Two types of protection is specified as follows: Basic Protection Fault Protection. Basic Protection: “Protection against electric shock under fault-free conditions” (from BS 7671 „Definitions‟). Basic Protection is provided to prevent a person or livestock touching parts that can normally be expected to be live under normal circumstances, e.g. live terminals, conductors, bus bars, etc. The example right shows a person coming in to contact with the line terminal of a socket outlet; the current returning via the person through earth back to the supply. This was previously referred to as “Protection against direct contact”. Fault Protection: “Protection against electric shock under single-fault conditions” (from BS 7671 „Definitions‟). Fault Protection is provided to prevent danger to a person or livestock touching conductive parts, whether forming part of electrical equipment (exposed conductive parts) or not (extraneous conductive parts), that would not normally be expected to be live but have become live due to a fault, e.g. gas pipes, water pipes, equipment enclosures, metal bath tub, structural steelwork, etc. The example below shows a person coming in to contact with a radiator that has become live due to it coming into contact with a line conductor.

The College At Clacton

Unit 17 Page 1

April 2012


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IT1 U17 - Protection - Complete by Bob Hibbert - Issuu