Page 662 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

Temporary bonding

While working in a dwelling you will no doubt have to cut into existing pipework
to add a new appliance, or take it away depending on the job specification.
This will mean that you will break the continuity bond between any exposed
metal or bonded material and ‘earth’. It is essential that the earth continuity
is maintained, and you can do this by using what is known as a temporary
bond – a 10 mm wire sheathed as earth that is attached to crocodile clips
2
which you can attach at each end. Once the work has been completed you
may remove the clamps and test for continuity again throughout the system.
If paint is present, you must ensure that it is removed fully to enable a sound
connection. There are some exceptions to bonding metallic pipes that have
insulated sections at their point of entry. You MUST consult regulation 411.3.1.2
of BS 7671 before cutting into or bonding any pipes.

Protection methods used on electrical

systems

Circuit breaker
The protective device in a consumer unit is also known as a circuit breaker
(CB). This is an automatically operated switch designed to protect an electrical
circuit from damage caused by overload or short circuit. You can also turn it
off manually to isolate individual circuits. When doing so it is advised that you
lock off the circuit breaker and perform the full safe isolation procedure before
any work commences. While work is being carried out, the circuit breaker must
remain securely isolated with warning signs posted.

Residual current device
A residual current device (RCD) is more sensitive than an CB, and when installed
in a consumer unit its job is to protect the ‘group’ of circuits. It is larger than an
CB and will have a test/reset button on its front. An RCD can be a lifesaver – it
works by constantly monitoring the electric current flowing along the circuit.
It is so sensitive that it can detect electricity flowing down an unintended path
– such as a person. If this happens the RCD will turn off the circuit within a
fraction of a second and prevent the person receiving an electric shock.

Rewirable fuses
Rewirable fuses were designed so that the wire (fuse) would burn and melt if
too high a current passed through it, disconnecting the flow. The only thing it
would detect would be a surge in the current above the specified level of the
fuse used. Fuse sizes were generally 5 amp, 15 amp and 30 amp. The fact that
the consumer could replace the wire if it had ‘blown’ led to many problems with
electrical fires. Many consumers did not realise the risks in trying to avoid the
inconvenience of the fuse tripping (by melting), and would put in a significantly
p Figure 11.9 Rewirable fuses larger wire or even a nail to keep this from happening.

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