PSSA Newsletter - March 2018

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ISSUE 18 March 2018 | NEWS
– 9 –
The Role of Pre-compliance
Testing in Electrical Product
Safety
There are four fundamental electrical safety tests that designers/
manufacturers/suppliers of electrical/electronic products should
employ during product pre-testing to assess if the product needs
further accredited testing or not. It relates specifically to products
covered by the Low Voltage Directive (LVD), those designed for use
at a rated voltage of 50–1000 V ac and 75–1500 V dc. The focus of
pre-testing should not obscure the fact that all the tests named in
the relevant harmonized standards are important unless they are
found to be not applicable. Nor should it be interpreted to slight
requirements to determine the levels of other risks presented by
an LVD product, including mechanical risks and the danger of fire,
explosion, burns, and other potential causes of death or injury.
Earth Continuity Testing
The earth bond test performs a measurement of resistance to
determine if the equipment would remain safe in the event that
internal live conductors touch the case. The test ensures that
sufficient current will flow through earth to blow the protective
fuse in the plug top or circuit breaker. It uses a high current from a
low-voltage test to make sure that earth connections are correctly
made. A failure indicates loose or poor earth paths. The earth bond
test applies to Class I equipment only; it cannot be used on Class II
equipment in which protection is supplied by double insulation.
Dielectric Strength Testing
Dielectric strength testing does not in fact involve a measurement
but rather is a procedure that aims to illustrate whether a product
remains safe when subjected to a high voltage. The test is designed
to determine if gaps or clearances between conductive parts and an
earth are sufficient and if degradation, such as pinholes and cracks
in insulation or other protective devices, has occurred as a result
of production processes or other sources of wear and tear. High
voltage is applied to the product to test the insulation between live
conductors and all exposed metal surfaces. For Class I equipment,
the high voltage is applied between the conductors and an earth. For
Class II equipment, the application point is between the conductors
and the outer surface of the product.
Insulation Resistance Testing
The insulation test acquires a measurement in megohms of the
resistance of a product's insulation protection by applying a dc
voltage between the phase (live) and neutral conductors to the
earth conductor for Class I equipment and between the phase and
neutral conductors to the outer case for Class II equipment. The
test is designed to ensure that protective insulation forms a barrier
sufficient to prevent electricity from coming into contact with a user
so as to cause injury, or to prevent other systems in the vicinity from
being adversely affected. Results of the insulation and other tests can
be used to fulfil this requirement
Earth Leakage Testing
The earth leakage test is the most misunderstood safety test. It was
devised to provide some measure of the quality of the insulation
resistance at line voltage potential when it is inappropriate or
impossible to perform dielectric strength or insulation resistance tests.
In any domestic or industrial power supply, a substantial current
normally flows from the live conductor through the various loads
motors, heating elements, and so on and returns to the neutral
conductor. This current then flows, via the neutral conductor, to the
local substation where it is bonded to true earth. This is literally the
"earth," or planet Earth. To provide protection and screening from the
live and neutral conductors, a third conductor, earth, is included.
Permissible levels of earth leakage current vary among product
types and related standards.
Elm Tree Consultancy can provide support and assistance with the
supply of Industry Standard Test Equipment enabling an organization
to demonstrate compliance with UK and CE Mark statutory
requirements for Routine Production Testing required as part of your
Technical File and encompassing appropriate ISO 9001 compliance
processes.
For further information contact: MikeWebb ElmTree Consultancy
on 07867 952116 or e-mail
PSSA Regulatory Briefing