5.1.3 - The disadvantages of earthing
The two important disadvantages are:
1. - Cost: the provision of a complete
system of protective conductors, earth electrodes, etc.
is very expensive.
2. - Possible safety hazard: It
has been argued that complete isolation from earth will
prevent shock due to indirect contact because there is no
path for the shock current to return to the circuit if the
supply earth connection is not made (see {Fig 5.3(a)}).
This approach, however, ignores the presence of earth leakage
resistance (due to imperfect insulation) and phase-to-earth capacitance (the insulation behaves as a dielectric).
In many situations the combined impedance due to insulation
resistance and earth capacitive reactance is low enough to allow a significant shock current (see {Fig
5.3(b)}).
Fig 5.3 - Danger in an
unearthed system
a) apparent safety: no obvious path
for shock current
b) actual danger: shock current via stray resistance
and capacitance
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