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Thursday, 31 August 2017
Mitigating Electrical Installation Risk as Standard
Recognising safety factors
Electrical installation standards exist to ensure the safety of people and infrastructure, with all elements of a cable management system working to achieve this, including the cable glands. Not all cable glands are equal in their level of protection or certification however, which may lead to serious safety concerns, so project owners and their engineers should exercise caution.
There are specific standards relating to the installation of cable glands. In most developed countries, safety requirements will be endorsed by local, national or international standards and subsequently written into national legislation. This ensures that electrical equipment is selected and installed to prevent physical harm or injury.
The prevailing standard IEC 62444:2010 and the European derivative EN 62444:2013 provide requirements and tests for the construction and performance of cable glands and have been developed for a variety of domestic, commercial and industrial applications.
In addition, cable glands used in explosive atmospheres should first meet the requirements of any relevant standard for industrial installation e.g. IEC 62444, and then comply with the requirements of IEC 60079-0 (general requirements), as well as IEC 60079-7 (Ex “e”) and IEC 60079-31 (Ex “t”) for example.
Adopting both IEC and EN 62444 standards allows cable glands with metric and NPT threads to be tested, certified and rated for a number of different mechanical and electrical attributes.
As a performance standard, IEC 62444 allows compliance with different degrees of ingress protection (minimum IP54), impact resistance, and cable pull out resistance, however, not all cable glands are tested or certified to IEC 62444.
The suitability of the product or equipment cannot be verified if it does not comply with a standard. A fully tested product will comply with all technical data related to impact values, electrical current values and cable retention categories, and will demonstrate evidence of obtaining 3rd party certification.
IEC 62444 applies to metallic and non-metallic cable glands and classifies cable glands according to the following:
- Mechanical properties
- Electrical current values (A, B or C)
- Sealing systems
- Resistance to external influences
- Cable retention twist tests
- Cable retention tests for non-armoured & armoured cable (class A, B, C or D)
- Resistance to impact (categories 1 to 8).
Establishing some basic product performance expectations for cable glands helps customers to form a specification; the importance of which should not be overlooked. The specification could include requirements for robust construction, corrosion resistant materials, reliability in design, and long term technical integrity of installations.
Over and Above 62444
Depending on the type of cable gland and the application, some users may require further tests, over and above those required by IEC 62444, including:
- EMC tests
- Vibration tests
- Salt water spray tests
- Enhanced testing for cable pull out
- Dynamic repetition flexion testing
Application Specific Requirements
As IEC 62444 is a performance standard which enables different compliance levels to be achieved, it is not enough for users to only ask for adherence to the standard. Moreover, it is imperative that the requirements are clearly documented in formal specification to ensure that the additional application requirements are captured relating across the cable management system.
By way of illustration, the mechanical protection of electrical enclosures in the IK Code system (IEC 62262) demonstrates that when properly tested to IEC 62444, cable glands may have a variety of different impact values:
IEC 62444 Table 4 – Impact values
- Categories : 1 (0.2 J) to 4 (2.0 J) equal to Domestic / Commercial Service Use
- Category : 5 (4.0 J) equal to Light Duty Industrial Service Use
- Categories : 6 (7.0 J) and 7 (10.0 J) equal to Medium Duty Industrial Service Use
- Category : 8 (20.0 J) equal to Heavy Duty Industrial Service Use
It would logically follow that the selected cable glands should maintain the same degree of protection as the electrical enclosure. This would include the minimum mechanical impact values of the IK code system (IEC 62262) being met which are more than adequately catered for by the IEC 62444 standard.
IEC and EN 62262 allow electrical equipment manufacturers to test and certify their products to obtain a rating with an IK code from IK02 to IK10; identifying the impact resistance from <1.0J to 20J. An impact resistance test allows engineers, designers and specifiers to select tested products and equipment to suit the applications defined by their environment.
Below is a typical illustration of mechanical protection and what the options may be:
- IK Codes : IK02 (<1.0 J) to IK07 (2.0 J) equal to Domestic / Commercial Service Use
- IK Code : IK08 (5.0 J) equal to Light Duty Industrial Service Use
- IK Code : IK09 (10.0 J) equal to Medium Duty Industrial Service Use
IK Code : IK10 (20.0 J) equal to Heavy Duty Industrial Service UseA similar theme also applies to electrical current values and cable retention tests; however the former only applies to cable glands made from conductive materials which are in direct contact with metallic cable sheaths; electrical values would not be applicable to nylon or polyamide cable glands.
Plastic cable glands may be suitable for use with some enclosure types, but it is important to ensure that they are mechanically robust and can be verified by this IEC 62444 impact value.
Steps to Safer Practice
Any products that may look the part but do not have the necessary 3rd party test certificates may become a safety risk if it cannot be proven that they fulfil all of the requirements of the relevant standard, in this case IEC or EN 62444.
Often seeing published data in manufacturers’ catalogues is still not enough and users should insist on verifying this by checking the third-party certification that the manufacturer should be able to provide for its products.
When evaluating cable glands, users should always take into account the relevance of current standards, both industrial and explosive atmosphere, as well as the verification of testing that should be carried out. This is ultimately the only way to prove that they are suitable for the environment.