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Selection & erection
All equipment must be correctly selected and erected. BS 7671
states that the following, along with manufacturer’s instructions
should be considered:
Compliance with standards
Operational conditions
External influences
Accessibility
Compliance with standards
A fundamental principle of BS 7671 is that all equipment must
comply with the appropriate British Standard. For distribution
boards BS EN 60439-3 is applicable.
If equipment has a foreign standard based on an IEC standard
then the designer or specifier must confirm that any differences
will not result in reduced safety.
Operational conditions
The electrical designer will need to select distribution boards for
operational conditions such as voltage, current and frequency.
In the UK the nominal voltage and frequency is typically
400/230V and 50Hz.
Installations and the distribution boards within them will, however,
have different current requirements. 512.1.2 in the 17
th
Edition
requires that the equipment is suitable for the design current and
the current likely to flow in abnormal conditions. The latter would
include short circuit and earth faults.
The specifier will therefore need to assess the current demand
taking into account diversity. They will also need to assess the
prospective fault current at the distribution board location before
selecting the board and the protective devices (see page 10).