Page 56 - 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

● At low levels of current (about 1 milliamp) the effect may be only an
unpleasant tingle but enough to cause loss of balance or a fall.
● At medium levels of current (about 10 milliamp) the shock can cause
muscular tension or cramp so that anything grasped is hard to release.
● High levels of current (about 50 milliamps and above) for a period of one
second can cause fibrillation of the heart, which can be lethal.
● Electric shock also causes burning of the skin at the points of contact.
Electric shocks are caused by a contact between a live conductor and earth.
An electric current will always attempt to earth itself, therefore if anything
comes between the flow of current and earth, the current will pass through it
depending upon its resistance to the flow of current. The human body, because
it contains 70 per cent water, is a very good conductor of electricity that offers
very little resistance to the flow of electric current.
Some materials are poor conductors and will therefore offer greater resistance
to the flow of electric current. Some of these materials, like PVC, are used to
shield the electricity and are called insulators.
Electric cables consist of a copper wire (an excellent conductor) and a PVC outer
cover or sheath (an excellent insulator). The result is a safe electric cable that
can be used as an electrical supply for tools and equipment.
Electric shock is not the only problem because electricity can produce great
amounts of heat, depending upon the size of the current and, if the current passes
through a flammable material, it can ignite the material, causing a fire or explosion.

Methods of safe electrical supply on construction sites
To comply with the EAW Regulations, employers are required to maintain their
electrical systems at work in a safe condition. According to the HSE, periodic
inspections and testing should be completed as part of this maintenance. More
than 1000 electrical accidents and incidents at work are reported to the HSE
every year and around 30 people, across all sectors of industry, die from their
injuries. The HSE reports that many deaths and injuries arise from:

● the use of poorly maintained electrical equipment
● work near overhead power lines
● contact with underground power cables during excavation work
● work on or near 230 V domestic electricity supplies, and
● fires started by poor electrical installations and faulty electrical appliances.

Electricity supply
The supply of electricity to homes and construction sites will normally be
provided by either:
● a public supply from a local electricity company
● a site generator, where the use of the public supply is not practicable or is
uneconomic.

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