Should copper or aluminum contact plates be selected when defining the technical specification of an Insulated Piercing Connector (IPC)?

When a customer intends to select an IPC (Insulated Piercing Connector) that they consider superior, more efficient, and more reliable for their overhead low-voltage electrical network, they very often face a dilemma as to which option is better in terms of energy efficiency, durability, installation speed, and the overall economic value of the IPC.

The most commonly requested options are:
-    tinned copper contact plates;
-    tinned aluminum contact plates.

An IPC (Insulated Piercing Connector) is designed to establish electrical contact by simultaneously connecting two conductors, which may be insulated or non-insulated, copper or aluminum. In terms of construction, these conductors may be sector-shaped, round, solid, stranded, or similar.

Contact is achieved in the following way: after the correct positioning of two conductors, which according to their function may be two main conductors (CDR-type connectors), one main and one branch conductor (CBS-type connectors), one main conductor and one for public lighting (CES-type connectors), or one main conductor and one for protective earthing (PMCC), the connector is tightened using a hand tool via a shear-off torque nut that serves to limit the tightening force. Once the specified torque is reached, the head of the nut is sheared off.

At the same time, the IPC (Insulated Piercing Connector) contact plates, which may be made of aluminum alloy or copper, penetrate through the insulation of the conductor and reach the metallic core, thereby establishing electrical contact.

Note: If the IPC (Insulated Piercing Connector) is installed on one or two non-insulated conductors, the contact plates directly lean on the conductor, apply pressure to it, and in this way establish electrical contact.

If we consider the aspect of insulation piercing on the main or branch conductor, which is most commonly encountered during the installation of IPCs on low-voltage (LV) aerial bundled cables (ABC), typically made of cross-linked polyethylene (XLPE), a material that is inherently quite rigid, especially at low temperatures, it can be concluded that, given the very similar hardness of the aluminum and copper alloys used for the contact plates, both types of contact plates perform the same function and therefore exhibit practically equivalent properties.

If we consider solely the electrical conductivity of the copper alloy, which is approximately 57 Sm/mm², compared to the electrical conductivity of the aluminum alloy, which is around 35 Sm/mm², it can be concluded that aluminum achieves approximately 61% of the conductivity of copper. Based on this data, it is clear that copper has a significant advantage.

The higher the electrical conductivity of the contact plate itself, the more energy-efficient the IPC (Insulated Piercing Connector) is. This means that during the flow of electric current through the IPC, a smaller portion of energy is lost through conversion from electrical to thermal energy. Accordingly, losses on the contact point are lower when the contact plates are made of copper alloy compared to aluminum alloy contact plates.

If we now consider these contact plates installed in an IPC (Insulated Piercing Connector) in the context of long-term operation and their durability, and base the analysis on testing according to the relevant international standard EN 50483-5:2010, the following observations were obtained:

•    The test is carried out through 1000 heating cycles on a formed electrical loop consisting of 6 IPCs (Insulated Piercing Connectors) of the same type, installed on appropriate conductors. During the electrical aging test, conducted through cycles of accelerated current-induced heating and cooling of the IPCs (Insulated Piercing Connectors), a specific characteristic was observed in connectors with copper contact plates installed on conductors with an aluminum or aluminum alloy core. Before reaching 750 cycles out of a total of 1000, excessive heating occurs, exceeding the upper permissible temperature limit.

From a detailed analysis of the test diagrams, it was concluded that during the specified heating and cooling cycles, the core of the aluminum conductor cools faster compared to the copper contact plates in the IPC (Insulated Piercing Connector). At a certain stage of the process, due to the insufficient ability of the copper contact plates to cool at the same rate as the aluminum or aluminum alloy conductor, the following occurs:

-    After approximately two-thirds of the total number of cycles, the temperature of the aluminum conductor becomes significantly lower than the temperature of the IPC (Insulated Piercing Connector) with copper contact plates. In other words, copper contact plates cool down more slowly and, in each cycle, retain a slightly higher temperature, which leads to its gradual accumulation over time.
-    This phenomenon is not observed in IPCs (Insulated Piercing Connectors) with aluminum alloy contact plates installed on conductors made of aluminum or aluminum alloys. It is also significantly less noticeable in configurations where one conductor, most commonly the main line, is made of aluminum or its alloy, while the other conductor, most commonly the branch line, is made of copper.

When it comes to installation speed, it does not directly depend on the type of contact plates material, but primarily on the design and geometry of the connector, and the design of contact plates. Modern industry trends, as well as the drive toward shorter installation times and greater connector universality, have led to numerous significant technical improvements.

Today’s customer expects the IPC (Insulated Piercing Connector) to be quick and easy to install, as well as designed in a way that ensures correct installation even in situations where a lineman or other trained person has insufficient experience or is not fully focused at the moment. In other words, the IPC (Insulated Piercing Connector) is expected to minimize the possibility of error through its design and to practically “correct” improper handling, ensuring reliable installation on low-voltage (LV) aerial bundled cables (ABC) or similar conductors.

In addition, there is a strong demand for greater universality of the IPC (Insulated Piercing Connector), meaning its ability to cover a wider range of conductor cross-sections. While the first IPC (Insulated Piercing Connector) of the CBS type, which appeared in the 1970s and 1980s, was often specified in the range of 16–25/35–70 mm², today available models cover a significantly wider range, e.g. 2.5–35/16–95 mm².

Such an expansion of the range and increase in universality has significantly facilitated the work of linemen, but at the same time it has required substantial technical improvements and continuous development of IPC connectors (Insulated Piercing Connector).

The concept of electrolytic (galvanic) corrosion, in the context of material selection for IPC (Insulated Piercing Connector) contact plates, emphasizes the fact that an IPC must have universal applicability, meaning that, as previously stated, it must meet the technical requirement of accommodating both aluminum and copper conductors.

In order for electrolytic corrosion to occur from a technical standpoint, two basic conditions must be met:

1.    The presence of two different (dissimilar) metals, where one acts as the anode and the other as the cathode.
2.    The presence of an electrolyte, i.e., in this case a humid environment.

When these conditions are fulfilled, electrons are transferred from the less noble metal (anode) to the more noble metal (cathode), which accepts the electrons. This process leads to the gradual degradation of the structure of the metals involved. From the perspective of IPC (Insulated Piercing Connector) operation, this mechanism can result in the degradation of the contact surface and the formation of a poor electrical connection. At the contact point itself, due to electrolytic corrosion and material degradation, an increased resistance occurs, i.e., higher energy losses through conversion of electrical energy into thermal energy. Ultimately, such processes can lead to serious and permanent deterioration of the IPC’s (Insulated Piercing Connector) functionality, as well as potential interruptions in the continuity of electrical supply.

It is important to note that this phenomenon typically occurs after a longer period of time, generally after 1–2 years of operation or later.

To minimize or completely eliminate this risk, various technical solutions are applied in the design of IPCs (Insulated Piercing Connectors), the most important of which are:

-    The use of waterproof elastomeric rubber, which prevents the ingress of moisture to the contact point.
-    The application of a special grease that provides additional protection of the contact surfaces against the effects of moisture.
-    Electroplating with a thin layer of tin (Sn) on the contact plates, regardless of whether they are made of copper or aluminum alloy.

Tin (Sn) is a metal that acts as an intermediate layer between copper and aluminum, thereby reducing the risk of electrolytic corrosion while also ensuring good electrical conductivity.

Design improvements in the new generation of IPCs (Insulated Piercing Connectors) also relate to the technological manufacturing process of the housing. Modern solutions involve a two-component design, where the housing is made of polyamide (PA), while the sealing part is made of elastomer (SEBS). Such a design is inseparable without the application of force, which on one hand makes the recycling process more difficult, but on the other hand significantly improves waterproofing and reliability.

Based on all the above findings regarding installation on aluminum and copper conductors, it can be concluded that tinned copper contact plates and tinned aluminum alloy contact plates behave in a practically equivalent manner.
Economic parameter: Based on the analysis of non-ferrous metal prices, primarily copper and aluminum, as well as the costs of the electroplating (tin-plating) process, it can be concluded that aluminum is significantly more cost-effective. Since the other IPC (Insulated Piercing Connector) components are identical, it follows that IPCs (Insulated Piercing Connectors) with contact plates made of tinned aluminum alloy represent a more economical solution.
Recycling parameter: From the perspective of recyclability and environmental impact, it can be stated that both IPC variants (Insulated Piercing Connectors)—with copper contact plates and with aluminum contact plates —exhibit practically identical characteristics and behavior.
•    Insulation piercing – no difference;
•    Electrical conductivity of the contact plate itself – copper 1 : aluminum alloy 0;
•    Electrical conductivity of the IPC (Insulated Piercing Connector) as a whole – no difference;
•    Installation speed – no difference;
•    Electrolytic corrosion – no difference;
•    Economic parameter / cost – copper 0, aluminum alloy 1;
•    Recycling and environmental impact parameter – no difference.

Author’s conclusion – Marel d.o.o. Serbia working group:

When defining the technical specification of the IPC (Insulated Piercing Connector), the customer, regardless of geographical region, may choose between copper or aluminum contact plates in accordance with their requirements, preferences, and experience, without significant risk and without essential differences in quality or performance.