Page 667 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 11 Electrical principles and processes for building services engineering

Table 11.2 shows a simple rule of thumb method for replacement of appliance
flexes. For flexes protected by the fuse in a BS 1363 plug there is no limit
to their length providing their cross-sectional areas (CSAs) are as stated in
Table 11.2.
 Table 11.2
Min. flex CSA (mm ) Fuse rating (A)
2
0.5 3
1.25 13

Other considerations such as voltage drop may limit flex lengths.

Components of electrical systems and

basic electrical tasks

Spurs and fused spurs
A spur is most commonly connected into a ring final circuit to add an additional
socket. A non-fused spur is commonly connected to a ring final circuit to add
one additional socket. An accessory known as a ‘fused connection unit’ (FCU)
can be included as part of an RFC or radial circuit to supply Items of equipment
such as combination boilers or underfloor heating, and is also commonly used
to supply S-plan or Y-plan hot water heating controls systems. From the FCU a
flexible cable will be used for direct connection to the item of equipment.

Spur from junction box

p Figure 11.19 Spurs and fused spurs

An unswitched fused connection unit is one that does not have a manual on/off
double pole switch, it only contains a fuse compartment and fuse. This type of
accessory is used to supply items of equipment where it is important to ensure
they cannot be easily switched off, e.g. security alarm panels.

You will probably also encounter double-pole (DP) switches. These break the
live conductors and when operated will provide complete isolation of the
connection unit. This item of equipment should always be placed in a lockable
position. The switch that forms part of an FCU will also be double-pole, and
a fuse compartment is also incorporated. This fuse compartment is designed

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