Handle larger wires with ease
March 2022
Among the most experienced electrical designers and technical professionals in the world or even an engineer new to the industry, large cable terminations are always considered to be challenging. However, there is a way to ensure that you can manage these larger cross section cables by following some practical procedures that make your terminations much easier and more efficient.
Terminating large cables in Power Terminal Blocks
Around the world, Power Terminal Blocks are often preferred for applications that use cables with larger cross sections. Typically, these range in size from 50 to 300 sq. mm . Termination of such large cross section cables on a terminal block raises complex challenges. The level of complexity varies based on several factors due to their close interdependency.
- Selection of Cable Rating, Size and Type of material
(Copper or Aluminium)
- Selection of Lugs
- Availability of proper Stripping and Crimping tools.
- Crimping of Lugs with cables
- Bending and laying of cables in ducts
- Mounting arrangement of Power Terminal Block
- Termination of power cable on the Power Terminal Block
Choosing the right Cable Rating, Size and Type of material (Copper or Aluminium)
The current rating is one of the important parameters while selecting a cable type and size of the cable and terminal block. Improper selection of the cable can lead to overheating of the current-carrying conductor of the terminal block. This can cause insulation failure, which can further lead to burning. The cable rating should be aligned to the rated current-carrying capacity of system and type of cable.
Selecting the correct type of lug
Always choose the right type of lug for the cable application. The lug you select should be based on the type of cable used, its current rating, internal hole diameter of the lug, with respect to the stud size, and contact area of lug, with respect to current carrying element. Ring type lugs are recommended for power cables. Using lugs of higher than the recommended size for termination often results in a loose cable joint. Choosing a bimetal lug and cable will lead to an improper joint and result in performance drops or faster corrosion damage. Hence, it is always recommended that copper lugs be used with copper cable.
Invest in proper stripping and crimping tools
To create a tight and proper connection, the crimping of a cable with a lug should be of a high standard. An effective crimping of cable with a lug can be achieved by using good quality cable stripping and crimping tools. Hydraulic or power crimping tools with the proper selection of die forms are recommended to ensure a good crimp operation. It is also necessary to ensure that cable stripping be done with care, to ensure that wire strands are not cut.
Improper crimping causes poor termination
The partial insertion of conductor in the lug, insertion of insulated cable or over-stripping, leads to improper crimping. Under crimping or over crimping of cable will also lead to loose contacts and allow an oxide film to form between the cable and the terminal. This results in increased resistance which can cause heat. Prolonged heat generation will lead to fire or melting of the Terminal Block.
Care while bending and laying of cables in ducts
Due to the large outer diameter of the power cable and its rigidity, bending and laying of the cable in a cable duct or in panel trunking is usually very difficult. During the bending of the power cable, the inside of the conductor may be mechanically damaged, and the mechanical damage may not be visible due to it being covered by the cable insulation. Hence, it is recommended that sharp bending of cables during installation be avoided.
Mounting arrangement of Power Terminal Block
The mounting arrangement is a critical factor for Power Terminal Blocks. While tightening the large cross section cables, the bending of the cable transfers force to the mounting feet of the terminal block. If a mounting arrangement is not adequate enough to take this force, the terminal block may get detached. Therefore, it is recommended that a suitable DIN rail be used that can attenuate the installation forces
Termination of power cable on the Power Terminal Block
While terminating large cross section cables, improper tightening of a cable can result in joint failure. Loose connection between the crimped cable and the terminal metal contact will lead to a greater resistance between the joints. This will cause increased voltage drop and overheating at the joint, which may lead to electrical failure. It is recommended that a good torque wrench be used to tighten the cable, within the recommended torque force for the terminal block, to achieve secure connection of cables.
It is also recommended that back support for the cable be provided while tightening the clamping bolt. This is to avoid deformation of the mounting rail or to prevent damage of the terminal block by torsion force. The presence of the spring washer or split washer must be ensured while tightening the nut and bolt arrangement.
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