Transcript Certification and Identification, Electrical Testing in

(Adapted from:D.T. Hall:Practical Marine Electrical
Knowledge)
 When a manufacturer produces an item of explosion
protected equipment, it must be tested and inspected
to ensure that it complies with the required standards
relating to that type of protection.
 All electrical apparatus and associated
circuits are required to be tested periodically
in accordance with a definite testing routine
with recorded test results.
 Insulation resistance, earth loop resistance
and earth continuity resistance tests are
required to be made, the last two in relation
to the setting or rating of the protective
devices associated with the apparatus and
its circuitry.
 It is important that insulation resistance
tests are NOT made in such a way that the
safety devices and insulation used in
intrinsically safe apparatus and circuits are
damaged by excess test voltages.
 No apparatus should be opened in a danger
area until it has been made dead and
effective measures (e.g. locking-off the
isolating switch) have been taken to prevent
its being made live again inadvertently.
 Where, for the purpose of electrical testing, it is
necessary to restore the
 power supply before the apparatus is reassembled,
tests should be made using a suitable gas detector and
continued during the operation to ensure that the
combustible does not approach the explosive limit.
 Unless the hazardous area can be made gas-free or
otherwise safe, or the electrical equipment is removed
from the area, then insulation resistance testing
should be carried out using a 500 V d.c. tester of
certified intrinsically safe (Exi) design.
 The testing and maintenance of flameprooj or
intrinsically safe equipment should be entrusted only
to competent persons who have received instruction in
the special techniques involved.
 The body material of instruments and tools required
for maintenance purposes should be designed so that
they will not make a hot spark when dropped.
 The energy output of all intrinsically safe instruments
should be so small that they do not produce hot
sparks. An insulation tester has a drooping
characteristic to prevent high currents and may be
intrinsically safe when applied to circuits of small
inductance or capacitance but a risk may arise when
such energy-storing properties of a circuit have an
appreciable value.
 Where such instruments are used the ( test leads
should be firmly connected throughout and on
completion of the test they should not be detached
until the circuit has been discharged through the
testing instrument (leave the tester for one minute
after test is finished).
 The previous sections covering zoning, gas grouping,
temperature classification and the various types of
protection methods show that the design of electrical
equipment for hazardous areas is very special.
 Maintenance of such apparatus must not, in
any way, cause its operation to be less safe
than in its original certified state.
 This most important point means that the
maintenance must be carried out by a
competent person. Temporary lash-ups,
refitting with wrong sized components (e.g.
lamps), failing to employ the correct
number of cover bolts etc., is absolutely
forbidden.
 The inspection and maintenance of Exd
(flameproof) enclosures for luminaires,
switches, junction boxes, push-buttons, etc.,
requires meticulous care.
 The following example gives a guide to the
inspection and maintenance points as
applied to a flameproof luminaire:
 This will reduce the enclosure strength. To
ascertain the extent of corrosion, remove
dirt, loose paint and surface corrosion with a
wire brush. If only the paintwork is
deteriorating, the enclosure should be
repainted to prevent further corrosion.
 Make sure that there are no missing bolts.
This is particularly important on flameproof
luminaires because a missing bolt will
invalidate the certification. Replacement
bolts must be of equivalent strength as
originals (usually high tensile steel).
 Ensure all mountings are secure. Corrosion
and vibration are severe on ships and can
cause premature failure.
 Examine the flamepath for signs of
corrosion or pitting. If the flamepath needs
cleaning, this should be done with a nonmetallic scraper and/or a suitable noncorrosive cleaning fluid.
 Examine the cement used around lamp-
glass assemblies both inside and outside. If
the cement is eroded, softened or damaged
in any way, advice should be sought from the
manufacturer regarding repair. If
deterioration of the cement has occurred, a
complete new lampglass assembly should be
fitted.
 Check lampglass; if cracked or broken a
complete new lampglass assembly should be
fitted. Clean the lampglass.
 When re-assembling an Exd enclosure you
must ensure that the following points are
covered:
 Lightly grease all flamepaths and threaded
components with an approved form of nonsetting silicone grease. Care must be taken
to ensure that blind tapped holes are free
from accumulated dirt or excessive grease
which can prevent the correct closure of
flamepaths, or cause damage to the tapped
components. Fit new lamp of the correct
rating.
 Ensure bolts are not over-tightened as this can
distort flamepaths, cause excessive stress on
lampglasses or distort weather proofing gaskets, if
fitted, allowing the ingress of liquids and dusts.
 Check the luminaire is installed in accordance
with the requirements of the installation,
particularly the classification of the area if it is
hazardous and that the correct rating of lamp is
fitted.
 Remove any build-up of dust on the luminaire, this
can cause overheating as well as acting as a
corrosive agent.
 Before attempting any maintenance work on
Exd equipment check for any particular
inspection and overhaul instructions given
by the manufacturer.