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Principles of High Integrity Electrical Connector Design

4 Jul, 2017

Three Principles of High Integrity Electrical Connector Design

Guest contributor: Carl Tamm, President of Classic Connectors USA.

Wouldn’t it be nice if our electrical conductors would grow like grape vines, beginning at the generating plant, branching off where appropriate, all the way down to the last twigs and leaves that represent our homes and businesses? One seamless conductor! Well, for a variety of reasons, our electrical infrastructure does not work that way. We require large, high voltage conductors to transmit our electrical energy to the general area of our load centers, where it is stepped down in voltage in sub-stations and distributed to those individual homes and businesses where it is stepped down further for our safety and convenience. This requires a plurality of conductors, and every one of those depends on a series of connectors to join them together and to terminate them on various types of equipment.

In our dreamy, fairy tale world of vines, and grapes and fine Barossa Valley Shiraz… Oh, excuse me; drifted off there a bit… our seamless world we might wish for is anything but seamless! Regardless of what tales you may have been told about “amalgamated” or “cold welded” connectors, every connector, regardless of the type or brand, has an electrical interface between it and the conductor, and it never goes away! The only exception to that statement is a thermal fusion welded connection. All others, whether they be bolted PG clamps, compression connectors, swaged connectors, setscrew connectors of various types, fired wedges, bolted wedges, even implosion type connectors – ALL – have an electrical interface – and that interface will degrade with time if it is energized! And given enough time and enough electrical current, that interface will increase in resistance until it causes a catastrophic failure of the circuit.

A common means of rejuvenating aged connectors is to provide a shunt type device. This article will address the use of Engineered Mechanical Shunts, of the brand name ClampStar® and will identify three crucial components of high integrity electrical connections and the significant advantage ClampStar Connector Correctors provide which affords them such dramatically superior performance in comparison to what most people have been led to believe to be the standard of connectors – the compression connector.

Let’s review some basics from Electricity 101, and trace those basics through the connectors in our circuits!

I = V / R

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across those two points and inversely proportional to the total resistance in the circuit. Thus, for a given current, the voltage across two points is proportional to the resistance between them.

Current follows the path of least resistance! This is not actually correct! Be careful what others may have told you in the past! Current will divide along multiple paths, proportional to the resistance of each path.

Now, let’s look at how these two principles relate to the electrical interface in the world of connectors! Approximately 90% of the current transfers from the conductor into the connector within 1cm of its first contact with the connector (area “A”). The remainder transfers at area “C” at the end of the conductor. There is no appreciable current transfer through area “B” in between. Why?

  • By design, a connector of this type has a greater cross-section of material, sufficiently larger than that of the conductor to compensate for any difference in resistivity of the two metals. This principle assures that a connector will have less resistance than an equivalent length of conductor! Therefore, the current on the outer strands will transfer to the connector body as soon as sufficient contact is achieved. This will represent roughly 90% of the current.

  • Current will divide proportionally through multiple paths dependent on the resistance of each path. Only the outer strands of the conductor actually make contact with the connector body. The inner strands have an interface between themselves and the outer strands, and this interface will have notably higher resistance than an unbroken section of the parent material. Therefore, the current on the inner strands will traverse to nearly the end, where it is essentially forced to transfer across the interface to the outer strands, and through them into the connector body.

  • Because current transfer depends on a voltage difference between two points, no current transfers in the center section, (area “B”) as the potential differential at this area is zero. This can easily be verified by drilling a hole in a connector down to the conductor strand, and placing one probe P1 on the surface or inside edge of the hole, and the other probe P2 in contact with the strand in the bottom of the hole!

The substantial current density near the mouth of the connector (area “A”) is such that localized heating occurs. This can be measured directly. Due to the current density and related thermal rise, upwards of 300°C at the interface, lower grade inhibitors break down, and like a candle, the current transfer area burns ever deeper into the connector over time. Note, you will not read 300°C on the outer surface of the connector. Due to the high thermal conductivity of aluminum, greater than 250 W/(mK) as one approaches 300°C, at the this intense heat is rapidly dispersed in every direction into the connector body – however, you will be able to measure increased heat at area “A” using a contact pyrometer. (For comparison, Iron is less than 60 W/(mK) at the same temperature).

The reason a ClampStar Connector Corrector operates so cool, even on extremely hot conductors exceeding 200°C, is because the ClampStar design only transfers current in the main body, along one side of the conductor as opposed to completely encircling it. Therefore, only 3 or four strands actually make contact right at the mouth, and each successive strand makes contact further down, effectively dispersing the current throughout the length of the body. The current transfer members are simply a much lower resistance than the conductor, so the entire unit remains comparatively cool, enough so that one can touch it with a bare hand without fear of getting burned!

Two other critical elements define the high integrity electrical connection. The next one to address is resilience! When we talk about transfer of electrical energy, our medium is the electron and the photon – and in the microscopic world of the atomic scale – think 10,000 orders of magnitude smaller than the comparatively huge “Nano-scale” technology – the electrical interface is a very dynamic place! Even small temperature differences result in colossal movement and dramatic interactions. Think of a geologic fault in earthquake conditions!

The property required to survive this is a resilient mechanism, which will move with this quake, and maintain the force that holds the electrical interface together. The ClampStar design incorporates both resilient stored mechanical energy in Belleville washers with its fasteners, and also in the deflections of the body components under varying stress levels. This assures that the mechanical forces generated during installation remain for long service life, and do not deviate with even extreme thermal cycling of 15°C to 200°C for hundreds of cycles.

The third critical element required to achieve not only high integrity initially, but to assure that integrity remains throughout many decades of extreme service conditions is inhibitor. The inhibitor used exclusively with ClampStar units is a proprietary blend, known as CC2 (say “see – see – squared), incorporating the most thermally stable carrier material availableand is highly conductive, increasing interface conductivity by 20% compared to common inhibitors. It is imperative that the inhibitor remains stable throughout all atmospheric conditions to which it may be subjected, preventing ingress of oxygen and electrolytes that incite corrosion. Incorporate these three principles into electrical connectors successfully and you have achieved the highest integrity in electrical connections – almost equivalent to a thermal fusion weld!

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