There are two areas of failure, physical failure of the connector, and electrical failure of the connector. While there are some designs in which only one or the other failures will occur, normally a combination of failures wilt take place.

 

Physical Failures

 

The physical failures generally result from the use of connectors which are not designed for the environmental conditions encountered. Unfortunately, even with all the thousands of designs on the market today, it is often very difficult to find a connector which will survive some severe environments, and when one is found, the limited market for such a design usually results in very high costs.

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The engineer specifying the connector has to face the decision of first cost vs replacement/maintenance costs and it is not unusual for the initial cost of the connector coupled with an apparently low replacement cost to account for the choice of connectors. But sometimes environmental effect costs due to increasing pollution levels are underestimated in the same way that long term maintenance costs due to rising labor costs are underestimated.

 

The most common physical failure results from corrosion eating away the parts of the connector holding the male and female components together. The result is that the connector simply disconnects. The cause of the corrosion is usually a lack of resistance of the connector body material and/or finish to the combination of salt/water and/or chemicals in the environment. The corrosion can be hastened by the use of materials which are incompatible galvanically, or by the use of the connector shell as both a physical coupling and a current carrying element.

 

Assuming that the connector cannot be replaced with a type more suitable for the climate, and that the connector is still functioning, the usual solution is to clean all traces of salt/corrosion from the connector, and re-assemble it, finishing by enclosing it in such a way as to prevent the entry of the contaminants. This may consist of "buttering" over the connector body with a high viscosity silicon grease and enclosing it in some sort of protective sleeve which will prevent the grease from being eroded away.

 

A second vulnerable area is the connection between the wire or cable and the connector itself. Many physical failures take place because salt water has penetrated into that part of the connector where the wires are crimped or soldered onto the pins. Quite apart from the electrical effects of the corrosion products, these products frequently occupy much more volume than the metal upon which they feed. Occasionally enough pressure can be generated to rupture a shell that has already been weakened by corrosion.

 

Sometimes it is necessary to use a supplementary means of cable/wire strain relief in order to minimize the effects of wind-induced vibrations in the cable in causing a "grinding" action between the two halves of the connector. A third type of failure is the exposure of the connector to unusual corrosive liquids or gasses not normally encountered in the environment, but which might be occasionally generated by other failures in the operating plant. This can also extend to corrosioninducing chemicals being liberated from connector components subject to overheating due to thermal runaway of contact-wire junctions.

 

This latter also suggests that we must also consider the possibility of other types of electric-current-induced physical failures. If the shell is being used as a conductor is there going to be sufficient heat rise caused by the combination of electrical resistance and current flow across the mechanical connection to cause physical failure of any of the other connector components, such as strain relief boots, seals, thermoplastic insulations, etc.? Could there be enough heat rise to cause failure of the electrical wire/cable connection to the connector?

 

It must be remembered that there are two elements involved in the electrical failure of a connector: the insulation, and the conductor/contacts/connections; in other words, the problem may involve the non-conductive parts and/or the conductive parts

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Dealing for the moment only with the part of the connector that is meant to disconnect and reconnect (and not with the parts that are attached electrically or otherwise, to the cable/wire; any connector may be broken down into a male-female or hermaphroditic component which is designed to mate with an equivalent part, and thereby pass electric current, and the parts needed to hold the former in alignment. The latter are usually insulators. In connectors carrying AC signals (especially higher radio frequencies) it is necessary to have the latter parts dimensioned so that the electrical impedance of the connector is the same as that of the cable - otherwise there will be a discontinuity and a reflection will occur in the transmission system.

 

Where the AC electrical impedance is not a consideration we have to deal with losses in or on the electrical insulation. Excessive leakage across the insulation will result in heating in high-power applications, insulation breakdown in high-voltage applications, or signal leakage in multiple pin control circuits. None of these are acceptable, and the consequences could be destruction of the connector and a fire hazard to consequential damages due to failure of a process-control, alarm, or communications system.

 

Where AC electrical impedance is a factor, insulation leakage can cause loss of signal strength and or unacceptable modification of the signal caused by line reflections. A good example of the latter is ghosts images or detail blurring in cable TV.

 

Failure of what patent attorneys like to call the "connector means" can range from a simple erratic connection (intermittent) to terminal failure of the contact pair.

 

The introduction of corrosion products into the gap between the connecting pair can also result in problems ranging from rectification effects (many corrosion products can create crude semiconductor junctions with metal surfaces) which can produce strange modulation distortion of the signals or even introduce spurious signals derived from the rectification of whatever RF (conventional RF of even fast rise time) signals may be present in the environment. Generally, this is characterized as excessive sensitivity to "electronic smog".

 

As before, the corrosion products can completely break the contact means or through its increased bulk, lock-up the connector so that it cannot be properly disconnected.