Cable Lugs Design and Safety Principles as Defined in IEC & UL Standard
Cable lugs help in the easy installation of cable termination and aid in the repair and maintenance of electrical devices or cables. Commonly, the lugs are used to connect one cable with another or to connect more than two cables through a busbar or any conducting medium. Some other uses are: connecting fuse sockets, load switches, and electrical appliances.
Specification and installation of the correct type of cable lug are important for power systems (LV, MV & HV) and their safe and reliable performance. Poor cable connections can increase joint resistance, fire, and fatality. Though they cost less than the cables, engineers and the cable jointers face difficulties in choosing from the wide range of Appliance wiring material (AWM) available for a specific application.
For the correct choice of cable lugs, a standardized approach to their construction and safety tests are critical. Two international organizations provide testing and certification on the cable lugs on various aspects of conforming to international standards.
International Electro-technical Commission (IEC):
The IEC, as an international standards organization offers international standards for all electrical, electronic, and related technologies or "electro technology". Along with other industrial applications, IEC standardizes technologies like power generation, transmission, and distribution, semiconductors for electrical cables. IEC also conducts conformity assessment and certifies if equipment, systems, or components conform to established international standards.
Underwriters' Laboratories (UL):
Underwriters Laboratory (UL) is global safety certification organization which conducts third-party testing that certifies the different type of products. Cable lugs and connectors come under the category of wire connectors and shall comply with the UL 486A-486B standard.
UL assigns different style numbers for each of the approved products; creates a style page that lists specifications, for example, AWM having a specification of a gauge size range, insulation material, temperature rating, and voltage rating for AWM. Each style specifies a product’s general use as determined by UL’s evaluation of the product. Figure 1 is an example of a style page for UL Style 1015. On UL-conformation, the manufacturer can place the certification mark on their products: "UL Listed" and "UL Recognized".
Cable lugs design and safety principles defined in IEC and UL standard covers the wide range of wire and cables available for various constructions. While IEC standards specify the minimum device safety requirements, the UL standard formulates comprehensive technical details for product safety and application.
IEC Safety Principles
IEC standards specify the minimum device safety requirements.
IEC control procedure certification will be based on the current edition of the design principles and standards published by IEC. Therefore the manufacturer must follow:
- The latest edition of the wiring rules
- Product standards
- Pass the initial testing to check that the installation complies with the standard and regulation
- A periodic check is performed as per recommendations.
Compression Lugs According to DIN 46235
DIN Standard 46235 ─ It defines the application, dimensions, and marking of cable lugs. This standard helps in using these lugs for compression of solid, stranded, fine stranded, and finest stranded copper conductors and cables. These lugs also indicate the number of required crimps. For installations, the DIN standard recommends crimping dyes as per the DIN 48083, Part 1, 3, and 4 for solid, stranded, and fine stranded conductors.
Besides the DIN cable lugs, Many manufacturers offer standard tubular cable lugs which are also made from electrolytic copper according to EN 13600 apart from the DN cable lugs. Normal tubular lugs are mostly shorter than DIN lugs. Their tube dimensions are also different.
Regardless of their type, all lugs can be crimped properly with a suitable cable crimping tool. Otherwise, proper crimp cannot be created which may cause increased joint resistance and temperatures and also fire.
The selection of a correct cable lug mainly depends on the type of cable. As per the DIN 57295 following lugs can be used:
- Cables Class 1, 2, 5, and 6: Compression lugs DIN 46235
- Cables Class 2: Standard tubular lugs
- Cables Class 2, 5, and 6: Terminals
However, flexible class 5 and 6 cable conductors may not fit into the appropriate cable lug. In that case, for the F-cable lugs having a larger inner diameter and flared entry indent crimping is recommended.
To install the DIN lugs, crimping tools that conform to the DIN 48083 Part 4 die codes should be used.
Recommendations for Electrical & Mechanical Properties
The IEC 61238 Part 1 applies to the electrical and mechanical properties of the cable lugs. This standard details the requirements for a permanent and safe electrical connection for the intended application. Both a mechanical pull-out test and an electrical durability test are defined.
A test cycle simulation is used to test the application. In this simulation, voltage peak in-rush in the public power supply system is created by heating the connection 1000 times (up to 120°C.) Besides, short-time high current tests also need to be carried out on the cable lugs at the temperature going upto 250°C.
All manufacturers of cable lugs must follow the IEC safety rules. Therefore, manufacturers specify the correct type of cable to be used with their lugs. Apart from the normal standards, manufacturers may use additional quality and safety requirements.
- Effectiveness and adjustments verification of RCD.
- Standardized human safety measurements against electrical shock and damage protection of property due to fire and heat.
- Installation safety by checking defects and confirming that no damage has occurred.
UL Safety Principles
UL standards specify across-the-board technical details concerning the safety and application of cable conductors. Manufacturers can voluntarily seek UL for testing and provide safety certification for their products.
In addition to standards development, UL is also responsible for UL certiﬁcation as well as ﬁeld acceptance.
Compliance with the standards is monitored strictly by UL, for example, through factory inspections of device manufacturers, to ensure that the framework conditions speciﬁed together with the certiﬁcation are met.
UL Standards for Lugs
Standard UL 486A-4886B describes the standard for cable lugs (Wire Connectors). It states:
- UL 486A-4886B standard states the requirement and specification of wire connectors which included all types of joints including cable lugs and connectors.
- This Standard applies to single-polarity connectors for use with all alloys of copper or aluminum, or copper-clad aluminum conductors, or all three, for providing contacts between current-carrying parts, investigated and found to meet the performance requirements of this
- The major test requirement consists of a Current Cycle test which is a test cycle simulation used to test the application. In this simulation, voltage peak in-rush in the public power supply system is created by heating the connection 500 times.
- Along with the electrical requirement of static heating and current cycling it also specifies the mechanical requirement which consists of pull out test and secureness test to check compliance of lugs as per standard.
- If the lug is anything other than the wrought copper, it will be investigated to evaluate if the lug performance will be the same as that of a wrought copper lug.
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