Extract From EN 60079-14 : 2003 / IEC 60079-14 : 2003
Installations In Hazardous Areas
1.0 Connections
The connection of cables and conduits to the electrical apparatus shall be made in accordance with the requirements of the relevant type of protection.
Notes:
- Certain types of cable employ materials which can exhibit significant "cold flow" characteristics which could have adverse effects on the protection of the apparatus. Where such cable is to be used, a suitable cable entry device should be employed, for example cable entry devices not employing compression seals which act upon the part(s) of the cable having "cold flow" characteristics.
- "Cold flow" can be more fully described as "thermoplastic materials which flow when subjected to pressure of ambient temperature".
Figure 1 - Selection chart for cable entry devices into flameproof enclosures for cables complying with item b) of 2.2 Selection
It is important to read notes and 2.2 Selection before selecting appropriate cable gland for flameproof applications from Figure 1 below:
NOTE - Internal sources of ignition include sparks or equipment temperatures occurring in normal operation which can cause ignition. An enclosure containing terminals only or an indirect entry enclosure (see 2.1 General) is considered not to constitute an internal source of ignition.
Extract From EN 60079-14 : 2003 / IEC 60079-14 : 2003
2.0 Cable Entry Systems
2.1 General
It is essential that cable entry systems comply with all the requirements referred to in the appropriate apparatus standard, that the cable entry device is appropriate to the type of cable employed, maintains the respective method of protection and is in accordance with clause 9.
Where cables enter into flameproof apparatus via flameproof bushings through the wall of the enclosure which are part of the apparatus (indirect entry), the parts of the bushings outside the flameproof enclosure will be protected in accordance with one of the types of protection listed in IEC 60079-0. Normally the exposed part of the bushings will be within a terminal compartment which will either be another flameproof enclosure or will be protected by protection type ‘e’. Where the terminal compartment is Ex‘d’, then the cable system shall comply with 2.2. Where the terminal compartment is Ex‘e’, then the cable system shall comply with 3.0
Where cables enter into flameproof apparatus directly, the cable system shall comply with 2.2
NOTE - Until further information is available, the use of aluminium conductors in Ex‘d’ flameproof enclosures should be avoided in those cases where a fault leading to potentially severe arcing involving the conductors may occur in the vicinity of a plain flanges joint. Adequate protection may be afforded by conductor and terminal insulation that prevents the occurrence of faults or by using enclosures with spigot or threaded joints.
Flameproof cable entry devices may be fitted with a sealing washer between the entry device and the flameproof enclosure providing that after the washer has been fitted, the applicable thread engagement is still achieved. For parallel threads, the thread engagement is normally five full threads or 8mm, whichever is the greater.
2.2 Selection
The cable entry system shall comply with one of the following:
a) cable entry device in compliance with IEC 60079-1 and certified as part of the apparatus when tested with a sample of the particular type of cable;
b) thermoplastic, thermosetting or elastomeric cable which is substantially compact and circular, has extruded bedding and the fillers, if any, are non-hygroscopic, may utilize flameproof cable entry devices, incorporating a sealing ring selected in accordance with figure 1;
NOTE 1 - If it has been shown that the use of a particular type of cable with a cable entry device in accordance with IEC 60079-1, and incorporating a sealing ring, does not result in ignition through external damage to the cable (caused by flame erosion) when subjected to repeated ignition of the flammable gas present in an enclosure, then full compliance with figure 1 may not be necessary.
c) mineral insulated cable with or without plastic outer covering with appropriate flameproof cable entry device;
d) flameproof sealing device (for example a stopper box or sealing chamber) specified in the apparatus documentation or having component approval and employing cable entry devices appropriate to the cables used. The sealing devices such as stopper boxes or sealing chambers shall incorporate compound or other appropriate seals which permit stopping around individual cores. Sealing devices shall be fitted at the point of entry of cables to the apparatus;
e) flameproof cable entry devices incorporating compound filled seals around the individual cores or other equivalent sealing arrangements;
f) other means which maintain the integrity of the flameproof enclosure.
NOTE 2 - Where a factory-made termination of the encapsulated type is used, no attempt should be made to interfere with the connection to the apparatus or to replace the cable.
Extract From EN 60079-14 : 2003 / IEC 60079-14 : 2003
3.0 Wiring Systems
3.1 General
Cables and conduits shall be installed in accordance with clause 9 and the following additional requirements concerning cable entries and conductor termination's.
3.2 Cable Entry Devices
The connection of cables to increased safety apparatus shall be effected by means of cable entry devices appropriate to the type of cable used. They shall maintain protection type ‘e’, incorporate a suitable sealing component to achieve the required degree of protection of the terminal enclosure (minimum IP54) and meet the mechanical impact strength requirements of IEC 60079-0.
NOTE 1 - To meet the ingress protection requirement it may also be necessary to seal between the cable entry device and the enclosure (for example by means of a sealing washer or thread sealant).
NOTE 2 - In order to meet the minimum requirement of IP54, threaded cable entry devices into threaded cable entry plates or enclosures of 6mm or greater thickness need no additional sealing between the cable entry device and the entry plate or enclosure providing the axis of the cable entry device is perpendicular to the external surface of the cable entry plate or enclosure.
Where mineral-insulated metal sheathed cables are used, the requirement to achieve creepage distances shall be maintained by using a suitable sealing device.
3.3 Conductor Terminations
Some terminals, such as slot types, may permit the entry of more than one conductor. Where more than one conductor is connected to the same terminal, care shall be taken to ensure that each conductor is adequately clamped. Unless permitted by the documentation supplied with the apparatus, two conductors of different cross-sectional area shall not be connected into one terminal unless they are first secured with a single compression type ferrule.
To avoid the risk of short-circuits between adjacent conductors in terminal blocks, the insulation of each conductor shall be maintained up to the metal of the terminal.
NOTE - Where single screw saddle clamps are used with a single conductor, the latter should be shaped around the screw in the form of a "U" unless clamping of single conductors without "U" is permitted in the documentation supplied with the apparatus.
3.4 Combinations Of Terminals And Conductors For General Connection And Junction Boxes
Care shall be taken to ensure that the heat dissipated within the enclosure does not result in temperatures in excess of the required apparatus temperature class. This can be achieved by:
a) Following the guidance given by the manufacturer relating to the permissible number of terminals, the conductor size and the maximum current, or
b) Checking that the calculated dissipated power, using parameters specified by the manufacturer, is less than the rated maximum dissipated power.
ACKNOWLEDGEMENT
Extracts from BS EN 60079-14 : 1997 reproduced with the permission of BSI under licence no. PD/1998 1818 and 1920. Complete editions of the standards can be obtained by post from BSI Customer Services, 389 Chiswick high Road, London. W4 4AL
