CABLE ENTRIES IN HAZARDOUS AREAS CORRECT … Presentations/2013/Arthur... · CABLE ENTRIES IN HAZARDOUS AREAS CORRECT SELECTION, INSTALLATION AND ... Because of these installation

S.A.F.A BRANCH PRESENTATION

CABLE ENTRIES IN HAZARDOUS AREAS CORRECT SELECTION, INSTALLATION

AND MAINTENANCE

Compiled by: Arthur Cameron


“NOT SO CORRECT”

SELECTION AND INSTALLATION OF CABLE

GLANDS AND JUNCTION BOXES IN

HAZARDOUS AREAS








INCORRECT INSTALLATION AND MAINTENANCE


INCORRECT INSTALLATION AND MAINTENANCE




SELECTION

METRIC

NPT

THREAD SELECTION


THREAD DIMENSION CHART


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?


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


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;


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


Problems With Cable Construction:

Has extruded bedding but not filled Extruded bedding and filled


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.


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


Barrier Gland Construction

CABLE

ARMOUR

CLAMP OUTER IP

SEAL ENTRY

THREAD COMPOUND

SLEEVE/

CHAMBER


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 ?


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?


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.


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.


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”.

?


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.


100% Effective Gas Barrier :


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.


(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


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


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.



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.



WE ARE ALL IN THE BUSINESS OF PREVENT…


QUESTIONS…

Documents

CABLE ENTRIES IN HAZARDOUS AREAS CORRECT … Presentations/2013/Arthur... · CABLE ENTRIES IN HAZARDOUS AREAS CORRECT SELECTION, INSTALLATION AND ... Because of these installation