Chapter 54
of the IEE Regulations gives details the earthing arrangements be
incorporated the supply system meet these Regulations and these are
described Chapter this book, under the heading ‘Electricity supply
systems’. The currents healthy
circuit will equal, but circuit that develops fault, some current will
flow earth and the line and neutral currents will longer balance.
IEE Regulation 411.2 tells that for final circuits not exceeding 32A the
maximum disconnection time shall not exceed 0.
Residual current protection
The IEE Regulations recognize the particular problems created when elec-
trical equipment such lawnmowers, hedge-trimmers, drills and lights
are used outside buildings.
Try This
Definitions
● What the Regulations mean ‘ordinary people’?
● Look back the definitions Chapter and write the margin here. The
RCD detects the imbalance and disconnects the circuit.3). (Table 12.4s.3.8 later in
this chapter shows RCD’s construction.2 41.4 the IEE Regulations.
Isolation and switching
Part the IEE Regulations deals with the application protective mea-
sures for safety and Chapter with the regulations for switching devices
.3.
An RCD type circuit breaker that continuously compares the current
in the line and neutral conductors the circuit.Overcurrent, short circuit and earth fault protection
237
The second element this protection method the provision means
of automatic disconnection the supply the event fault occurring
that causes the exposed metalwork become live.
The achievement these disconnection times dependent upon the
type protective device used, fuse circuit breaker, the circuit conduc-
tors the fault and the provision adequate protective equipotential
bonding. The Regulations, there-
fore, require that any socket outlet with rated current not exceeding 20A,
for use ordinary people and intended for general use shall have the
additional protection residual current device (RCD) which has rated
operating current not more than milliamperes (mA) (IEE Regulation
411. these circumstances the availability an
adequate earth return path matter chance. The resistance, call the impedance, the earth fault loop
must less than the values given Appendix the Site Guide and
Tables 41.2 later this chapter
shows the maximum value the earth fault loop impedance for circuits
protected MCBs 60898. Figure 12.) will look this again later this
chapter under the heading ‘Earth Fault Loop Impedance ZS’
