Handbook of Electrical Installation Practice - BeKnowledge

264 Handbook of Electrical Installation Practice
It is expected that the supply will be via underground cable, where practicable,
and suitably protected or distant from areas of potential damage from ground
anchors, etc. The individual supply terminal equipment or distribution unit is to be
adjacent to each site pitch and BS 7671 makes specific requirements in terms of the
terminal equipment in so far as the enclosure positioning, socket-outlet specification
and related overcurrent protection are concerned. It also recognises that supplies
in excess of 16A may be required. It is required that the pitch supply position
is located so that it is accessible for the caravan to connect to with normally a 25m
flexible cable.
It is a requirement to provide protection against indirect and direct contact by
means of a suitable residual current device. It is convention to group pitches
together electrically; if this is done then groups of up to three socket outlets may
be protected by the same device. Groups of caravans must be fed from the same
phase.
A network that feeds a large caravan site will normally be an underground
system that will require considerable care in design. The use of small distribution
pillars can allow for a main distributor system on either a ring or radial system
which can be combined with smaller service-type cables to individual groups of
pitches.
It should be noted that in the event of a PME supply being provided for a caravan
site, the caravan sockets must not be connected to the PME terminal. Instead, earthing
arrangements should be as with a TT system with the protective conductors of
caravan supply sockets connected back to an earth rod. This is underscored by a
special reference to caravans in the statutory regulations, which instructs that where
PME systems are employed, the supply neutral conductor must not be connected
to any metalwork in any caravan.
HIGHWAY POWER SUPPLIES AND STREET FURNITURE
The risks
The risks are from:
• Wetness
• Proximity of earthed metal
• Proximity of live parts
• Arduous conditions
• Potential for working at high level
Potential for working amidst traffic.
•
The protective measures
Normally electrical equipment used for highway power supplies shall have a
minimum IP rating of IP33, but most equipment is rated IP 65.
In view of the traditional means employed of mounting some items of street furniture
on DNO poles, BS 7671 makes some concessions as to the use of protection