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S.A.F.A BRANCH PRESENTATION
CABLE ENTRIES IN HAZARDOUS AREAS CORRECT SELECTION, INSTALLATION
AND MAINTENANCE
Compiled by: Arthur Cameron
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“NOT SO CORRECT”
SELECTION AND INSTALLATION OF CABLE
GLANDS AND JUNCTION BOXES IN
HAZARDOUS AREAS
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INCORRECT INSTALLATION AND MAINTENANCE
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INCORRECT INSTALLATION AND MAINTENANCE
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SELECTION
METRIC
NPT
THREAD SELECTION
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THREAD DIMENSION CHART
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Factors to consider when selecting cable glands: • Dimensional, • Mechanical, • Constructional, • Environmental factors.
SELECTION
Cable: • Type of cable, armoured or unarmoured? • Sizing over the inner sheath and outer sheath. • Shape and construction of the cable. Is the cable
round, filled and non hydroscopic?
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IEC60079-14 - 10.4.2 SELECTION OF CABLE GLANDS
START
Does this enclosure contain an internal source
of ignition?
Does the hazardous gas
require IIC apparatus?
Is the area of installation
Zone 1?
Is the volume
of the enclosure greater than
2dm3?
Use a suitable flameproof cable
entry device with a sealing ring.
(Gland with Elastomeric Seals)
Apply 10.4.2
d) or e)
NO YES
YES NO
YES NO
YES NO
S.A.F.A BRANCH PRESENTATION
IEC60079-14 - 10.4.2 SELECTION OF CABLE GLANDS
d) flameproof sealing device (for example a sealing chamber) specified in the equipment
documentation or complying with IEC 60079-1 and employing a cable gland appropriate to
the cables used. The sealing device shall incorporate compound or other appropriate seals
which permit stopping around individual cores. The sealing device shall be fitted at the point
of entry of cables to the equipment;
e) flameproof cable gland, specified in the equipment documentation or complying with
IEC 60079-1, incorporating compound filled seals or elastomeric seals that seal around
the individual cores or other equivalent sealing arrangements;
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Problems With Cable Construction:
In order to comply with the installation codes of practice, cable glands using elastomeric sealing rings should
only be used on cables that are substantially round, compact with an extruded bedding and have non
hygroscopic fillers such as Figure 1.
However this cable construction is not always possible especially when it comes to multi core cables.
Figures 2 and 3 show cables that should not be used with glands with elastomeric sealing rings.
Figure 1 Figure 2
Interstices
Square not round
Figure 3
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Problems With Cable Construction:
Has extruded bedding but not filled Extruded bedding and filled
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Selection IEC 60079-14 Section 9.3 States:
“NOTE: Where enclosures are likely to be subjected to large variations in ambient and/or service temperature
conditions, a ‘pumping’ action can transfer the fluids from the hazardous atmosphere through cables which are
not substantially compact. Similarly cables with non filled interstices or with hygroscopic fillers (e.g. fiber fillers),
may transmit flammable fluids through the interstitial spaces of the cable under capillary or hygroscopic action
with sufficient partial pressure to exit the cable termination at the extremities of the cable.
Particular caution is drawn to the use of electro-pneumatic transducers and the like which employ natural gas as their
pneumatic medium. When such cables link between a hazardous and non-hazardous area this may result in a flammable
atmosphere being transported to the inside of, for example, control room equipment. The situation is likely to be most acute
with equipment installed in a Zone 0 or Zone 1 location (where the presence of a hazardous atmosphere has a greater
likelihood and duration). If these conditions are likely to apply, a cable sealing device (which seals between the inner sheath
and the individual conductors) should be used”.
Therefore it has been established that if unfilled cable is used explosive gases or liquids can migrate down the
interstices of a cable from a hazardous area into a safe area.
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Hazardous Area
Zone-1
Safe Area
An explosion in the Ex d enclosure can propagate down the
interstices of the cable causing damage to the cable as well
as forcing pressure into a non certified enclosure.
Exd
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Barrier Gland Construction
CABLE
ARMOUR
CLAMP OUTER IP
SEAL ENTRY
THREAD COMPOUND
SLEEVE/
CHAMBER
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Where cables enter into Ex d equipment directly, the cable system shall comply with 10.4.2.
The standard goes on to say in note 2 under 10.4
“Gas or vapour migration and propagation of flame may occur through the interstices between the strands of standard
stranded conductors, or between individual cores of a cable. Special cable construction can be employed as means
of reducing migration and preventing the propagation of flame. Examples include compacted strands, sealing of the
individual strands, and extruded bedding.”
10.4.2 outlines the selection process for cable gland for Exd equipment as follows:
10.4.2 Selection of cable glands
The cable entry system shall comply with one of the following:
a) Cable glands in compliance with AS/NZS 60079.1 and certified as part of the equipment when tested with a sample
of the particular type of cable;
b) where a cable has thermoplastic, thermosetting or elastomeric insulation and is substantially compact and circular
with extruded bedding and fillers that are non-hydroscopic; a flameproof cable gland, in compliance with AS/NZS
60079.1, may be utilized, providing this incorporates a sealing ring and is selected in accordance with Figure 2
When To Use Barrier Glands ?
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Gas Explosion incident :
At 8pm on monday12 January 2004,
the South East Australian Sea Gas System
Control centre received an alarm.
A water heater installed at the Torrens Island
facility had failed.
Investigations revealed that a gas explosion
had taken place inside the heater control panel
located outside of the classified area.
HOW COULD THIS HAPPEN?
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Gas Explosion Incident:
Buckled enclosure door
and broken latches due to
explosive forces.
Further investigation revealed that
gas had migrated along the cables
from field instruments in the
classified area and significantly also
passed through the epoxy filled
barrier glands and accumulated
inside the control panel.
This gas was ignited when the
cooling fan inside the panel
activated, thus causing the
explosion.
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The Cause: Badly Installed Barrier Glands:
Barrier compound installed
incorrectly
Compound hasn’t bonded
to the cable insulation
leaving voids for gas to
pass through.
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Time taken and Risks of Installing Epoxy Putty Barrier
Glands: For a number of years installers in hazardous areas have been relying on barrier glands with two part epoxy
based putty as a way of effectively stopping explosive gasses and liquids from diffusing down unfilled cables.
Whilst effective once properly installed, the problems with the two part putty based compound have always been
the time taken to mix the putty and then insert and pack between the cables voids and into the barrier gland
chamber.
The mixing process can take several minutes depending on the volume of putty required and has always been
subjective as the putty is only properly mixed when the two parts are hand moulded into an “even colour”.
?
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Time taken and Risks Of Installing Epoxy Putty Barrier
Glands:
The insertion of the putty between the individual cores of multi core cable is not only time consuming but
there could be additional risks in that the putty may not have been inserted and packed correctly which
results in the potential of voids and gaps for gas or liquids to migrate through.
In addition once the putty has been inserted between the cable cores and the barrier chamber, the time
taken for the putty to harden can be up to several hours.
Because of these installation problems barrier glands have always required special skills from the installers
and particular attention from inspectors.
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100% Effective Gas Barrier :
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Installation Codes and Standards
Equipment Construction
and Protection Techniques
Entry Size and Thread form of
the Equipment.
Cable Type and Size
Environmental Conditions and Risks.
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(a) Initial Inspections:- These inspections are directly related to required inspections before equipment will
be commissioned for the first time e.g. on cable glands checking that the marking and certification is correct, checking tightness and that all components have been correctly fitted and not left out.
(b) Periodic Inspections:- It stipulates that the interval between periodic inspections shall not exceed two
years, and shall be shorter if the deterioration of the apparatus could influence explosion protection sooner.
c) Sample inspections:- Sample inspections are inspections of a portion of the installed apparatus. This can
be visual, close or detailed. The size and composition of all samples should be determined taking into account the purpose of the inspection. The result of all sample inspections should be recorded.
Surface Industry:
INSPECTION and MAINTENANCE
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VISUAL INSPECTION: Visual inspections take note of all defects which can be determined by a visual approach either from the ground or from permanent access platforms, without the use of hand tools, without switching off and without climbing or using ladders. Binoculars and remote heat detecting equipment may be useful in some situations. In the case of a cable entry device no dismantling is required.
GRADES OF INSPECTION
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CLOSE INSPECTION: Close inspections determine where any defects, including those detectable visually, may be detected without removing power. This may involve the use of some tools, ladders and other access mediums. In the case of a cable entry device a general check on tightness is required.
GRADES OF INSPECTION
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DETAILED INSPECTION:
Detailed inspections are also carried out at
major shut down periods, normally on a
sample basis. They include the disconnection
of power and include opening up equipment.
Access equipment, tools and test equipment
may be used.
In case of a cable entry devices: check
tightness of cable glands (using a tool). If
the gland corrosion is a possibility,
partially dismantle the gland to check the
earthing of cable armour onto the gland.
GRADES OF INSPECTION
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WE ARE ALL IN THE BUSINESS OF PREVENT…
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QUESTIONS…