Seaward B255 - Manual (Page 14)

Operating Manual Clare B255 Power Tool & Appliance Test Station
10
Test Requirements to Determine Electrical Safety
The most appropriate way of verifying Electrical Safety is to carry out a series
of routine Safety Tests that both reflect those tests used in the manufacturing
process and, particularly in the Hire Industry, take into account the effects of
normal wear and tear.
Visual Inspection
It is important when carrying out routine testing to first check for signs of
undue wear and tear by a thorough visual inspection – a nick in the supply
cable or a cracked casing etc can easily lead to hazardous situations when
the power tool or appliance is in use.
Electrical Safety
The tests to verify satisfactory ‘earth bonding’ and insulation levels will
depend on –
a. The basic construction of the tool –
Class I/Earthed or Class II/Double Insulated and
b. The original standard that it was manufactured to-
the most common British Standards relating to equipment used in the Hire
Industry being BS EN 50144 for hand held power tools and BS EN
60335-1 for general appliances, however clear guidance should be sought
from the manufacturer, or importer, to determine appropriate requirements.
Earth Bond Continuity
Most type testing standards, including those referred to above, require that
the earth bond resistance between all accessible conductive surfaces and the
‘Earthing’ terminal within the item, does not exceed 0.1 Ohm. Compliance
should be checked by resistance measurement using a test current equal to
1.5 times the rated current or to 25A, whichever is the greater, from an a.c.
voltage source not exceeding 12V.
In practice, routine testing will always include the supply lead and the
measurement will be made between the earth pin of the supply plug and
exposed metal (conductive) surfaces of the tool.
As a generalisation, most power tools will still meet the 0.1 Ohm limit, and an
earth bond resistance up to 0.3 Ohms may be acceptable when supply leads
up to 5 metres in length are included. This figure can be further increased by
0.1 Ohm for each additional 5 metres of supply lead length, but this may also
be dependent on the cross-sectional area (csa) of the conductor being used.
NOTE Where exposed metal parts cannot be seen to form a continuos
surface with all other exposed metal, such as a metal grille in a plastic housing
or a remote switch panel, OR where moving guards or detachable accessories
are also made of metal, measurements must be taken from all surfaces back
to the Earth pin of the plug top.