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

NVQ2 Electrical Installations
132
●
●
●
●
sufficient slack should be left inside the joint box to prevent excess tension on
conductors
cables should be inserted so that they are not crossing; they should be neat and
fitted so that the lid fits without causing damage
correct size joint boxes should be used
joint boxes should be secured to a platform fitted between the floor and ceiling joists.
Phase
Neutral
cpc
switch
switch feed switch wire
Joint box
Neutral
Figure 6.16 illustrates the control of one light via a one-way switch using this method.
Rings, radials and spurs
Before the early 1950s different types and sizes of socket outlet and plug were in use
in domestic premises, which was very annoying and inconvenient! In 1947, 5 A and
15 A socket outlets were deemed obsolete, and agreement was reached on a standard
13 A socket outlet with a fused plug, to BS 1363. In this section we will be looking at
the standard power-circuit arrangements found in domestic premises. In particular
the following will be investigated:
●
●
●
ring circuits
Figure 6.16 One-way switch using a joint box
permanently connected equipment
non-fused spurs
Ring circuits
●
●
fused spurs
radial circuits.
In this system the phase, neutral and circuit protective conductors are connected
to their respective terminals at the consumer unit, looped into each socket outlet
in turn and then returned to their respective terminals in the consumer unit, thus
forming a ring. Each socket outlet has two connections back to the mains supply.
Lamp