Introduction
Cable glands are mechanical cable entry devices and can be constructed from metallic or non-metallic materials. They are used throughout a number of industries in conjunction with cable and wiring used in electrical instrumentation and automation systems.
Cable glands are mechanical fittings that form part of the electrical installation material. The purpose of a cable gland is to seal the cable and retain it in the electrical equipment that it is attached to. It should maintain the ingress protection rating of the enclosures, keeping out dust and moisture but it should also prevent the cable from being pulled out of the equipment and from being twisted whilst connected to equipment. If it is intended for use with armoured cable, the cable gland also provides an earth continuity function.
Cable glands may be used on all types of electrical power, control, instrumentation, data and telecommunications cables. They are used as a sealing and termination device to ensure that the characteristics of the enclosure which the cable enters can be maintained adequately.
Cable Gland Standard
For industrial electrical installations the need for compliance with standards is vital in order to ensure such things as occupational health and safety in the workplace, security and safety of earthing systems, functional safety, longevity of performance and continuity of supply for plant and equipment. The same criteria which are applied to the plethora of electrical equipment should also be considered as applicable to cable glands, in order for systems to be installed and operated reliably.
During the formative years of the rapidly expanding power generation industry in all over world, the acute need for a common standard reference document that could address cable gland requirements was recognised, and from this GDCD 190 was created. Latterly in the 1970’s BS 4121 was superseded by BS 6121 with the introduction of the metric system of measurement across Europe. Majority of cable gland designs around the BS 6121 standard. However in particular the area where some manufacturer don’t comply with BS 6121 are the maximum bore dimensions (Table-I) through the cable gland, the wall thicknesses as a result of the bore size discrepancies, and the sealing ranges that differ considerably from the standard.
European standard for Cable Glands EN 50262 was published in September 1998. The new standard is very different from the previous British standards BS 6121 in some important respects. A new IEC standard for “Cable Glands for Electrical Installations”, IEC 62444, was published in 2010 and in time this will be adopted in several countries across the world, including Australia. This new standard could have a profound impact on users and manufacturers, especially those who discover for the first time that the products they have previously used have not been tested to any current standards. IEC 62444 is similar to EN 50262 in that it is also a performance based standard, allowing manufacturers to produce cable glands of varying degrees of robustness some of which may be more suited to light industrial applications such as factory automation, whilst others may be more applicable to medium and heavy duty industrial electrical installations, such as power generation and distribution.
Nomenclature
Cable Gland Construction Requirements
A. Cable Gland Retention
A circular test mandrel is loaded until the pull force is in accordance with the values given in Table 2 column “Cable retention”. For test mandrels which are not circular in shape, i.e. where non-circular cables are being simulated, their cross-sectional area shall be determined, and the diameter of a circular cable of the same cross-sectional area shall be calculated. The test values shall be appropriate to the nearest circular test mandrel size. For cable glands with sealing systems comprising two or more seals with different sizes, the mandrel shall be stepped appropriately. The test values shall be appropriate to the largest test mandrel diameter. The test mandrel is marked when unloaded so that any displacement relative to the cable gland can be easily detected. The load is maintained for 5 min and at the end of this period the displacement shall not exceed 3mm when unloaded. The test is repeated using new samples and a test mandrel equivalent to the maximum value of the sealing range of the cable gland as declared by the manufacturer or supplier, with the test value of the relevant maximum cable diameter specified in Table 2.
B. Cable Anchorage Test for Non-Armoured Cable
Compliance is checked by the following tests. For cable glands with a sealing system in accordance with 6.5.1, a test mandrel equivalent to the minimum value of the anchorage range of the cable gland as declared by the manufacturer or supplier is fixed to the sample. For cable glands with a sealing system in accordance with 6.5.2, a test mandrel equivalent to the minimum value of the anchorage range of the smallest orifice of the cable gland is fixed into the smallest orifice of the sample, and each remaining orifice is plugged with a plug equivalent to the minimum value of its sealing range. The test mandrel is marked when unloaded so that any displacement relative to the cable gland can be easily detected. The test mandrel is pulled 50 times for a duration of 1 Second without jerks in the direction of its axis with the relevant pull force specified in Table 2. At the end of this period the displacement shall not exceed 2mm. This measurement is to be carried out after unloading the force from the test mandrel. A typical arrangement for the cable anchorage pull test is shown in Figure 2.
C. Cable Anchorage Pull Test
The sample with the test mandrel is then mounted onto the test arrangement for the cable anchorage twist test as shown in Figure 3. The test mandrel is marked when unloaded so that any displacement can be easily detected and then is subjected for 1 min to the torque as shown in Table 3. During this test the test mandrel shall not turn by more than an angle of 45°. The pull and twist tests shall be repeated using a test mandrel equivalent to the maximum value of the anchorage range of the cable gland as declared by the manufacturer or supplier with the test value of the relevant maximum cable diameter specified in Tables 2 and 3.
D. Cable Anchorage Test For Armoured Cable
Two samples, each consisting of two cable glands, are assembled. In the first sample, the cable glands are fitted, one at each end, to a cable 300 mm long, with the maximum over armour diameter as declared by the manufacturer or supplier. In the second sample the cable glands are fitted, one at each end, to a cable 300 mm long, with the minimum over armour diameter as declared by the manufacturer or supplier. For each sample, one cable gland is fixed and the other cable gland is loaded in accordance with the appropriate value given in Table 2. The cable is marked so that any displacement relative to each cable gland can be easily detected. The load is maintained for 5 min and at the end of this period the displacement shall not exceed 3 mm at either cable gland. A typical arrangement for cable anchorage test for armoured cable is shown in Figure 4. Following the test, the samples of cable glands classified in accordance with 6.3.1.2 shall then be subjected to the test in accordance with 10.2. Following the test, the samples of cable glands classified in accordance with 6.3.1.3 are then subjected to the test in accordance with 10.2 followed by the test in accordance with 10.3.2.
E. Resistance to Impact
Compliance is checked by the following test. For cable glands with a sealing system in accordance with 6.5.1, a test mandrel equivalent to the minimum value of the sealing range of the cable gland as declared by the manufacturer or supplier is fixed to the sample and then the test is carried out at the minimum temperature in accordance with 8.5 or lower if declared by the manufacturer. For cable glands with a sealing system in accordance with 6.5.2, a test mandrel equivalent to the minimum value of the sealing range of the smallest orifice of the cable gland is fixed into the smallest orifice of the sample, and each remaining orifice is plugged with a plug equivalent to the minimum value of its sealing range. The test is carried out at the minimum temperature in accordance with 8.5 or lower if declared by the manufacturer. Prior to the impact test the samples shall be placed in a refrigerator for 8 h minimum. The test temperature tolerance is ± 2 °C.
The testing can be done – inside the refrigerator at the declared minimum temperature, or – outside the refrigerator at ambient temperature (20 ± 5) °C if the cable gland previously was cooled down to the declared minimum temperature in accordance with 8.5 minus 5 °C and the impact is carried out within (15 ± 2) after the cable gland was removed from the refrigerator. For example, if the declared temperature is –20 °C and the test is carried out outside the refrigerator, then the cooling temperature shall be –25 °C. The point of impact shall be the place considered to be weakest. The sample shall be mounted on a steel base so that – the direction of impact is perpendicular to the surface being tested if it is flat, or perpendicular to the tangent of the surface at the point of impact if it is not flat; – there is no movement of the cable gland support which could influence the test results. The mass shall be fitted with an impact head of hardened steel in the form of a hemisphere of 25 mm diameter. The base shall have a mass of at least 20 kg or be rigidly fixed or inserted into the floor. A typical arrangement for the impact test is shown in Figure 5. The sample is subjected to the impact energy as given in Table 4 according to the category declared by the manufacturer or supplier.
Cable Gland Selection Chart
Information
What is ATEX ?
ATEX is the name commonly given to the framework for controlling explosive atmospheres and the standards of equipment and protective systems used in them. It is based on the requirements of two European Directives:
1. ATEX 99/92/EC Directive
Also known as ‘ATEX 137’ or the ‘ATEX Workplace Directive’. Minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres. The text of the Directive and the supporting EU produced guidelines are available on the EUwebsite. For more information on how the requirements of the Directive have been put into effect in Great Britain see the information in the section on Equipment and protective systems intended for use in explosive atmospheres.
2. A TEX 94/9/EC Directive
Also known as ‘ATEX 95’ or the ‘ATEX Equipment Directive’. ATEX 94/9/EC was removed and replaced by a new Directive 2014/34/EU from April-2016.
Equipment and protective systems intended for use in potentially explosive atmospheres. The aim of this directive is to allow the free trade of ‘ATEX’ equipment and protective systems within the EU by removing the need for separate testing and documentation for each member state. The regulations apply to all equipment intended for use in explosive atmospheres, whether electrical or mechanical, including protective systems. The text of the Directive and EU produced supporting guidelines are available on the EU website. For more information on how the requirements of the Directive have been put into effect in Great Britain see the section on Selection of equipment and protective systems.
Objective of the ATEX Directive 2014/34/EU
The objective of Directive 2014/34/EU is to ensure free movement for the products to which it applies in the EU territory. Therefore the directive, based on Article 95 of the EC Treaty, provides for harmonised requirements and procedures to establish compliance. The directive notes that to remove barriers to trade via the New Approach, provided for in the Council Resolution of 7 May 1985, essential requirements regarding safety and other relevant attributes need to be defined by which a high level of protection will be ensured. These Essential Health and Safety Requirements (EHSRs) are listed in Annex II to Directive 2014/34/EU.
These essential health and safety requirements are specific with respect to
* Potential ignition sources of equipment intended for use in potentially explosive atmospheres ;
* Autonomous protective systems intended to come into operation following an explosion with the prime objective to halt the explosion immediately and/or limit the effects of explosion flames and pressures;
* Safety devices intended to contribute to the safe functioning of such equipment with respect to ignition source and to the safe functioning of autonomous protective systems ;
* Components with no autonomous function essential to the safe functioning of such equipment or autonomous protective system(s) Since 1st July 2003 relevant products could only be placed on the market in the EU territory7, freely moved and operated as designed and intended in the expected environment if they comply with directive 94/9/EC (and other relevant legislation).
Directive 2014/34/EU provides for the first time harmonised requirements for non-electrical equipment, equipment intended for use in environments which are potentially explosive due to dust hazards and protective systems. Safety devices intended for use outside explosive atmospheres which are required for or contribute to the safe functioning of equipment or protective systems with respect to risks of explosion are also included. This is an increase in scope compared to former national regulations for equipment and systems intended for use in potentially explosive atmospheres.
Explosive Atmosphere
In Great Britain the requirements of Directive 99/92/EC were put into effect through regulations 7 and 11 of the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).
The requirements in DSEAR apply to most workplaces where a potentially explosive atmosphere may occur. Some industry sectors and work activities are exempted because there is other legislation that fulfils the requirements. These exemptions are listed in regulation 3 of DSEAR
In DSEAR, an explosive atmosphere is defined as a mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
Atmospheric conditions are commonly referred to as ambient temperatures and pressures. That is to say temperatures of –20°C to 40°C and pressures of 0.8 to 1.1 bar.
Many workplaces may contain, or have activities that produce, explosive or potentially explosive atmospheres. Examples include places where work activities create or release flammable gases or vapours, such as vehicle paint spraying, or in workplaces handling fine organic dusts such as grain flour or wood.
Explosive atmospheres can be caused by flammable gases, mists or vapours or by combustible dusts. If there is enough of the substance, mixed with air, then all it needs is a source of ignition to cause an explosion.
Explosions can cause loss of life and serious injuries as well as significant damage. Preventing releases of dangerous substances, which can create explosive atmospheres, and preventing sources of ignition are two widely used ways of reducing the risk. Using the correct equipment can help greatly in this.
The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) place duties on employers to eliminate or control the risks from explosive atmospheres in the workplace. A summary of those requirements can be found below.
Where can Explosive Atmospheres be found ?
Many workplaces may contain, or have activities that produce, explosive or potentially explosive atmospheres. Examples include places where work activities create or release flammable gases or vapours, such as vehicle paint spraying, or in workplaces handling fine organic dusts such as grain flour or wood.
What does DSEAR require?
DSEAR requires employers to eliminate or control the risks from dangerous substances – further information on these requirements can be found on the DSEAR web page[6]. In addition to the general requirements, the Regulations place the following specific duties on employers with workplaces where explosive atmospheres may occur.
Classification of areas where Explosive Atmospheres may occur
Employers must classify areas where hazardous explosive atmospheres may occur into zones. The classification given to a particular zone, and its size and location, depends on the likelihood of an explosive atmosphere occurring and its persistence if it does. Schedule 2 of DSEAR contains descriptions of the various classifications of zones for gases and vapours and for dusts.
Selection of Equipment and Protective Systems
Areas classified into zones must be protected from sources of ignition. Equipment and protective systems intended to be used in zoned areas should be selected to meet the requirements of the Equipment and Protective Systems Intended for use in Potentially Explosive Atmospheres Regulations 1996. Equipment already in use before July 2003 can continue to be used indefinitely provided a risk assessment shows it is safe to do so.
Hazardous Area
A “hazardous area” is defined as an area in which the atmosphere contains, or may contain in sufficient quantities, flammable or explosive gases, dusts or vapours. In such an atmosphere a fire or explosion is possible when three basic conditions are met. This is often referred to as the “hazardous area” or “combustion” triangle.
When electrical equipment is used in, around, or near an atmosphere that has flammable gases or vapours, flammable liquids, combustible dusts, ignitable fibers or flyings, there is always a possibility or risk that a fire or explosion might occur. Those areas where the possibility or risk of fire or explosion might occur due to an explosive atmosphere and/or mixture is often called a hazardous (or classified) location/area. Currently there are two systems used to classify these hazardous areas; the Class/Division system and the Zone system. The Class/Division system is used predominately in the United States and Canada, whereas the rest of the world generally uses the Zone system.
A. Zoning Classification
Hazardous locations as per the Zone system are classified according to its Zone which can be gas or dust. For gas atmospheres electrical equipment is further divided into Groups and Subgroups.
Zone
The Zone defines the probability of the hazardous material, gas or dust, being present in sufficient quantities to produce explosive or ignitable mixtures.
B. Group Classification
The Type of Hazard
The type of hazard will be in the form of either a gas or vapours or a dust or fiber. The classification of these hazardous is primarily divided into two groups depending on whether it is in a mining or above surface industry. These are defined below:
Group I : Electrical equipment for use in mines and underground installations susceptible to firedamp.
Group II and Group III: Electrical equipment for use in surface installations.
Group II : Gases are grouped together based upon the amount of energy required to ignite the most explosive mixture of the gas with air.
Group III : Dusts are subdivided according to the nature of the explosive atmosphere for which it is intended.
Groups II & III are further sub-divided depending upon the hazard.
C. Protection Concept
Protection Type:
To ensure safety in a given situation, equipment is placed into protection level categories according to manufacture method and suitability for different situations. Category 1 is the highest safety level and Category 3 the lowest. Although there are many types of protection, a few are detailed.
Ingress Protection (IP)
Ingress Protection (IP) rating are developed by the European Committee for Electro Technical Standardization (CENELEC) (NEMA IEC 60529 Degree of Protection Provided by Enclosure -IP Code), specifying the environmental protection the enclosure provides.
The IP Rating is an accepted engineering standard for defining the protection of electrical equipment from dust and moisture ingress. For pressure sensors and associated instrumentation the 2 digit version of the IP rating is used to indicate how well the design will prevent dust and water getting into the electronic enclosure.
The IP rating normally has two digits :
1st Digit : Protection from solid objects or materials
2nd Digit : Protection from liquids (water)
IP First digit – Protect against solid objects or materials
The higher the first digit of IP rating, the better the ingress protection from dust, sand or dirt particles penetrating the outer enclosure and damaging the internal components.
D. Temperature Classification
Another important consideration is the temperature classification of the electrical equipment. The surface temperature or any parts of the electrical equipment that may be exposed to the hazardous atmosphere should be tested that it does not exceeds 80% of the auto-ignition temperature of the specific gas or vapours in the area where the equipment is intended to be used.
The temperature classification on the electrical equipment label will be one of the following (in degree Celsius):
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