Terminations - Devil's in the Details

Terminating conductors may seem to be a menial task, but make no mistake – it is important. Mistakes here could cause hours of troubleshooting or other types of problems after continued hours of use and aging of the installation. NEC 2017 has recognized the importance of this task as well. Let’s explore this topic further and shed some light on what many think can be left to the most inexperienced on the job. I think you may see that this task deserves closer attention.


There may not be an immediate cause and effect when it comes to terminations gone wrong as some problems may take quite some time to manifest themselves. The following are some identifiable problems that poor terminations can cause: 

Heat: Loose connections due to not being torqued properly can come loose over time and introduce impedance that reacts with the current to cause heat. The heat only acts to further degrade the connection point. Excessive heat at a termination can damage equipment on either side of the termination, whether it be the insulation of the conductor or the equipment to which the conductor is attached.  

Oxidation: Aluminum quickly develops a layer of oxide when exposed to air. This oxidation is highly resistive. Proper plating is required or other paste-type products applied on the termination.  

Corrosion: Dissimilar metals can introduce corrosion. This acts to introduce more impedance into the circuit, and if this connection is your ground return path or an equipment grounding system, then your path of least resistance can be compromised and your grounding system not quite as effective as you had hoped. Corrosion can occur in aluminum conductors due to galvanic action. Galvanic action occurs if dissimilar metals are used in an electrolytic solution.  

Thermal Linear Expansion Coefficient: This is the fractional change in length of a particular material, for each degree of temperature change. This can cause loose connections, which could result in heating.

Creep: Creep is the continued deformation of material under stress. The aluminum alloy 1350, which was used and associated with problems many years ago – no longer an issue – had a much higher creep rate than copper.

Voltage (Over/Under): If a termination is not made correctly and the wire to the load or from the source does not make the connection needed, you may experience a reduced voltage or even an overvoltage. Your overvoltage condition is a good example of losing the neutral on the line side of a residential home’s main load center. I have seen a handful of examples of this on homes where the neutral from the utility – either in the meter or even at the transformer – caused an overvoltage in the home damaging electronics.

Arcing: Arcing from phase to phase, phase to neutral, or even phase to ground can occur if bare conductors touch equipment or other bare conductors. Stripping the insulation from the conductor before termination and damaging the insulation during termination can introduce opportunities for arcing faults to occur. 

NEC Violation: As you will see below, there are many areas in the code that focus on termination points. When mistakes are made, an inspector might be able to point out the problem and the NEC Section it violates. 

Miss-Operation: Improper voltage, high impedance paths, and arcing and sparking as well as other effects of poor terminations may cause equipment to not operate as expected. Whether it be sensitive electronic equipment, industrial control equipment, a grounding system solution, or more, mistakes in terminations may be a cause of miss-operation.   

Violate UL Listing: If care is not taken in your terminations, you may be applying the product outside of its UL listing. Products are tested under certain conditions and test configurations. These are reflected in manufacturer’s instructions a