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Modern Electrical Installation for Craft Students, 3rd Edition
book

Modern Electrical Installation for Craft Students, 3rd Edition

by Brian Scaddan
November 2013
Intermediate to advanced content levelIntermediate to advanced
182 pages
6h 6m
English
Newnes
Content preview from Modern Electrical Installation for Craft Students, 3rd Edition
116 Control and earthing
Test
push
and
resistor
b
Diagram 85 (a) Residual current device; (b) circuit of residual current
device.
The test switch creates an out-of-balance condition which trips the
breaker. Its only purpose is to indicate that the breaker is in working
order. It does not check the condition of any part of the earth system.
Out-of-balance currents as low as 20 m A to 30 m A will be detected,
and therefore a person touching unearthed live metalwork would cause
the breaker to operate before the lower lethal limit of 50 mA was
reached
(Diagram
86). It is still necessary, however, to ensure that the
earth system of an installatio ...
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Publisher Resources

ISBN: 9781483106205