.Basic Electrical Installation Work
330
or distortions the mains supply and many computers incorporate filters
which produce high protective conductor currents around 3mA. However, the loss supply mainframe computer com-
puter network for even second can cause the system ‘crash’, and hours
or even days work can lost. IEE Guidance Note
7 recommends that equipment should connected double sockets
as shown Fig.1 μF
FIGURE 14. mains supply.1 and deals with the earthing requirements for the installation of
equipment having high protective conductor currents.44.
Clean supply
Spikes, caused over voltage
transient surging through the mains
‘Noise’: unwanted electrical signals picked
up power lines supply cords
FIGURE 14. Mainframe com-
puters and computer networks are sensitive mains distortion interfer-
ence, which referred ‘noise’.
To avoid this, ‘clean’ supply required for the computer network. This
is clearly not fault current, but typical the current which flows the
CPC equipment under normal operating conditions.
Secure supplies
The mains electrical supply the United Kingdom extremely reliable
and secure.45
A simple noise suppressor. 14. clean earth can also taken from this
point, which usually one core the cable and not the armour SWA
cable, and distributed around the final wiring circuit.45.
Clean supplies
Supplies computer circuits must ‘clean’ and ‘secure’. supply.44
Distortions the a. 14.
Double socket outlets must have two
terminals for protective conductors. Noise mostly caused switching an
inductive circuit which causes transient spike, brush gear making
contact with the commutator segments electric motor. IEE Regulation
543. These distor-
tions the mains supply can cause computers ‘crash’ provoke errors
and are shown Fig. One
terminal used for each protective
conductor, minimum size 1.
One solution this problem protect ‘precious’ software systems
with uninterruptible power supply (UPS).7. 14.
FIGURE 14.c.43
Recommended method connecting equipment socket outlets.5mm2
Separate
connections
Distribution
fuse board
PE
Ring final circuit supplying
twin socket outlets
(total protective conductor
current exceeding 10mA).c.43. Alternatively, the
computer supply can cleaned means filter such that shown in
Fig. UPS essentially battery
supply electronically modified provide clean and secure a.
This can provided taking the ring radial circuits for the computer
supplies from point close possible the intake position the
electrical supply the building.
C R
R100Ω
C0
