If you've ever had to work on a project where you needed to connect two cables, then there's a considerable chance you've had to work with cable joints. These components do a great deal to keep the flow of electricity going when cables are broken, and their work is critical to ensuring the integrity of your connection.
In this article, we'll take a quick look at cable joints, the available types, and how you can make the right choice when deciding.
In its simplest terms, a cable joint is an electrical connection component that forms when two or more electrical cables are physically joined together.
Given that these physical connections can lead to different outcomes, a cable joint's job is to ensure that electricity flows continuously and safely. Most cable joints are used when you ned to branch or extend cables, especially in telecomms, power distribution, or industrial applications.
A high-quality cable joint is especially favored because it can perform several important functions, including the following:
Ensuring Continuity with the Insulation: An ideal joint keeps current flowing while also maintaining its insulation integrity to prevent any leakage.
Extending Cable Runs: Cable joints also keep cables linked together whenever the needed insulation distance gets too long for the available cable.
Fixing Cable Damage: When you notice that a part of the cable becomes compromised, you can use a cable joint to restore it without having to replace the whole thing.
Protecting the Cable: Modern cable joints come with features that allow them to withstand considerable levels of strain and physical stress.
To really understand the types of cable joints available, we must first break these components down based on specific classifications:
When considering the level of voltage that the joints will need to contend with, we can break them down into the following:
These cable joints are mostly used for systems that don't exceed 1 kV. For residential wiring and low-voltage distribution networks, they're perfect.
These are cable joints built to handle networks between 1 kV and 33 kV. They provide improved insulation and stress control, as well as better sealing techniques.
Then, we have the cable joints that operate in high-demand power transmission systems that are rated well above 33 kV. These cable joints come with better insulation materials, the ability to relieve stress, and accurate installation processes that help them handle these massive electrical loads.
Here, you have two main categories to consider:
These joints are used in cables that are placed on cables and other elevated spaces. Due to their location, it's important that they withstand exposure to the sun, rain, wind, and rapid temperature changes.
The direct opposite of their overhead counterparts, underground cable joints are buried underground. So, they need optimal moisture prevention and resistance to both pressure and chemicals in the soil.
Finally, we can classify cable joints based on the material of their conductor:
For cables with copper conductors, these joints are perfect. They provide impressive conductivity, as well as the mechanical strength needed to handle heavy-duty networks.
Cable joints used with aluminum conductors will need special jointing techniques and compounds that can resist oxidation and maintain contact stability at all times.
Over the years, different types of cable joints have been developed in response to shifting power generation demands. In this section, we'll take a closer look at the major types of cable joints, as well as what makes each option unique.
To get us started, let's consider straight joints. Known to some as inline joints, these are by far the most common cable joint type. They're built to connect two ends of a cable in a straight path, and they are mostly used to extend an existing cable's length or fix a damaged section without the need to get a new cable.
Primarily, straight cable joints are built to:
Ensure continuity in the electrical connection.
Restore insulation levels to what the original cable had.
Project against the environment and the effects of tension
Where They Are Used:
Straight joints are mostly used in low and medium-voltage distribution systems. You can also find them in industrial power systems, street lighting projects, and more. You can use them for both underground and overhead power lines and count on them to provide seamless use over long distances.
Branch or T-joints have a unique design that allows you to tap a new cable line directly into an existing main feeder. This schematic creates a branch connection with a “T” shape, hence giving the joint its name and allowing you to distribute electric power to different locations all from the same source.
With T-joints, you can:
Ensure flexibility in network expansion
Provide power distribution to different directions
Get solid insulation and reduce electrical losses as you branch from high-load circuits
The joints are famous in electrical distribution networks, particularly in urban settings where you need to route power to buildings, utilities, and other substations.
The transition joints are specially built to connect cables that have different insulation or construction types. For instance, when you need to link a Cross-Linked Polyethylene (XPLE) cable to a Paper-Insulated, Lead-Covered (PILC) cable, this is the joint you want to use.
Thanks to their unique design, transition joints help to properly manage different insulating properties and offer stress-control devices to electrical fields. The joints also focus on reducing moisture entry and chemical interactions across materials.
As for their applications, transition joints can be used to:
Upgrade power networks, especially when you can't just replace all cables at once
Integrate modern cables with older electrical infrastructure
Modernize HV and MV networks
These are essentially traditional cable joints that are filled with a resin or gel-like insulating compound to prevent the entry of moisture into the joint. They're incredibly moisture-resistant, with their simple design that still works quite well for wet environments.
In terms of application, we see these insulation joints used in:
Telecommunications connections
Underground electrical installations
Environments that are prone to floods
The heat shrink joint is one of the most common types of cable joints in the world today. These joints make use of dedicated tubing that forms a tight shrink around the cable as soon as you apply heat, leaving you with a stable protective seal that prevents external entry.
In a heat shrink joint, you can have components like heat shrink insulation tubes, a protective jacket on the outer part, stress-control tubes, and even a conductive crimp. With this build, you get the following advantages:
Optimal sealing and insulation
Strong resistance to environmental elements, from moisture to UV light and more
A lightweight build that you can transport easily
Even better, the heat shrink joint works in both indoor and outdoor installations. Technicians love them because they're easy to install, and they use them from underground projects to distribution substations and more.
We also have cold-shrink joints, which offer a safer and more contemporary alternative to the heat shrink joint. These joints are made from elastic tubes that have been held in place by a core. When you pull the core out, the entire tube shrinks naturally onto the cable, meaning that you don't need any additional heat.
With this build, cold shrink joints provide:
No need for a heat source or an open flame
A great fit for dangerous environments
Quicker and more consistent in installation
Where They Are Used:
You mostly use cold shrink joints in installations where you can't use heat tools due to safety regulations. You can also use them in very cold environments where a heat shrink joint just isn't so practical. So, everything from mines to petrochemical facilities and more falls into this category.
With polyurethane and resin joints, you take the connection and place it in a mould. Then, you fill it with a strong insulating resin that forms a protective layer around the joint after the curing process takes place.
The build is advantageous because:
It's incredibly strong
It can work in different abrasive conditions
It strongly resists moisture and other forms of external stress
General Applications:
Resin cable joints work for buried low- or medium-voltage networks. You can also use them for lining subsea cables and other industrial applications where heavy machinery will be used.
Since they cure into a solid block, these joints offer impressive long-term viability, even in pressurized underground environments.
When selecting a cable joint, you want to be very careful to ensure reliability, safety, and the type of performance you want in the long term. Choosing the wrong joint can lead to serious electrical faults, so watch out for the following factors when selecting.
Before anything else, you want to consider the system's overall voltage rating. Each cable joint is specifically designed to handle particular voltage levels:
Low-Voltage (LV) Joints: LV cable joints are usually rated up to 1 kV. They're mostly used in residential and light commercial applications.
Medium-Voltage (MV) Joints: Unlike the LV cable joints, the MV cable joints are rated between 1 kV and around 33 kV. For substations, urban distribution networks, factories, etc., MV cable joints are ideal for you.
High-Voltage (HV) Joints: The HV cable joints are rated for anything above 33 kV. This means you can use HV cable joints for power transmission, underground networks, and other heavy-duty applications.
You also need to consider the cable's physical characteristics. Primarily, focus on:
Cable Size: If you're working with a larger conductor, you need a joint that can also handle massive current loads and mechanical strain. In fact, some of these joints can come with different connector options and crimp sizes so as to accommodate multiple diameters.
Conductor Material: You will need to use different joining techniques if you're working with aluminum or copper cables. For instance, aluminum is prone to oxidation - meaning it will need compounds and connectors that resist oxidation in order to keep conducting.
By choosing a joint that works with both conductor material and size, you can ensure a reliable electrical connection and reduce the overheating risk.
If you need a cable for allocation like an underground duct or an industrial plant, you want to make sure the joint can easily handle oil, moisture, corrosive agents, and more.
For cases like these:
Choose resin-filled or polyurethane joints since they resist chemicals and mechanical force.
Heat-shrink and cold-shrink joints are also great because they have additional mechanisms to prevent water entrance.
For underground installations, pot/jelly-filled joints do well to protect your components.
Finally, factor in the expected maintenance needs. This allows you to choose a joint that balances ease of maintenance and long–term durability across the board.
Permanent Joints: Resin, polyurethane, or heat-shrink joints tend to last longer and offer maintenance ease.
Reusable or Easily Serviceable Joints: You'll have a much easier time inspecting cold-shrink joints or modular mechanical joints. So, for temporary installation, you might want to consider these.
Cost vs Durability: As usual, you'd have to pay more for high-quality joints. But, considering that they won't need much repair or maintenance, they're worth the money.
Cable joints are an important part of any safe electrical connection - especially when it involves multiple cables. However, knowing the right type - as well as the factors to consider when choosing - will save you a great deal.
Want to learn more? We at Haivol Electrical are always here to help you out. Reach out to us today!
Yes, but you will need a transition joint that can connect cables of different insulation types or materials. This allows you to optimize insulation compatibility and keep the current flowing.
A cable joint's lifespan will depend on its type, the quality of the insulation, and the environment in which you install it. High-quality joints can easily last between 20 and 30 years, although things like exposure to chemicals and moisture can also affect their operating lifespan.
Issues like faulty insulation and loose connections are minor and won't be a problem to fix - especially for LV cable joints. But, for safety and reliability - especially when it comes to MV cable joints and HV cable joints, we'd recommend replacing the entire joint for safety.
