Handbook of Electrical Installation Practice - BeKnowledge

262 Handbook of Electrical Installation Practice
The risks
The risks are from:
• Wetness
• Minimal clothing
• Arduous conditions
Temporary nature of connections.
•
The protective measures
General
BS 7671 disallows certain protective measures for caravans and, in practical terms,
installations will usually employ insulation and enclosures as protective measures
against direct contact, and earthed equipotential bonding and automatic disconnection
of supply (with supplementary protection by residual current device) as
the most likely protective measure against indirect contact.
Because a caravan may require to be fully functional when low voltage is not
available, extra low voltage battery circuits are normally also employed. The
separation of low voltage and extra low voltage, and the temporary nature of the
electricity supply connection arrangements within a potentially metallic structure,
require special consideration in relation to the design of systems and the protective
measures to be employed.
The provision of a residual current device in the caravan gives the user protection
against indirect and direct contact, irrespective of the caravan park supply
arrangements. Without this independence the user relies on the caravan park operator
to provide and maintain an essential protective measure on his behalf and this,
in some circumstances, may not be acceptable.
It is a requirement that extraneous-conductive-parts of the caravan should be
bonded to the circuit protective conductor. However, on the basis of the definition
of an extraneous-conductive-part being that which is ‘. ..liable to introduce a potential
etc.’, metal sheets forming part of the structure of the caravan are not required
to be bonded.
Selection and erection of equipment
Wiring systems are required to be of flexible or stranded conductor construction,
with a minimum cross-section area of 1.5mm 2 . Furthermore, cables are to be supported
at intervals of not more than 0.4m vertically and 0.25m horizontally. Special
attention is drawn to the need to bush or similarly protect cables where they pass
through metalwork. These requirements are all due to the movement and vibration
likely to be incurred by a caravan in motion. Generally, there may not be any wiring
accessories with accessible conductive parts excepting fixing screws.There is concern