Chapter 6 - Level 2 NVQ and Technical ... - Pearson Schools

Exposed and extraneous conductive parts
On completion of this topic area the candidate will be able to list exposed conductive
parts and extraneous conductive parts of metallic structures and services.
Exposed conductive parts
These are the metallic parts of an electrical system, which can be touched and which
are not normally live. However these can become live under fault conditions.
Examples of exposed conductive parts are:
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metal casings of appliances such as heaters
kettles
ovens
wiring containment systems such as metal conduit, cable tray and trunking.
Extraneous conductive parts
These are metallic parts within a building, which do not form part of the electrical
system, but can also become live under fault conditions. Examples are:
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water and gas pipes
air conditioning
boilers
air ducting systems
structural steel work of the building.
Earth protection
On completion of this topic area the candidate will be able to state the purpose of
earthing and the function of earth protection.
Purpose of earthing
By connecting to earth all metalwork not intended to carry current, a path is
provided for leakage current which can be detected and interrupted by fuses, circuit
breakers and residual current devices. Figure 6.22 illustrates the earth return path
from the consumer’s earth to the supply earth.
Chapter 6 Basic electrical circuitry and applications
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