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 and can be found in the UL White Book. When a product is applied incorrectly, the safety of the application could be at risk as the configuration may have never been tested.
The above are just some of the ramifications that can be experienced when you do not make proper terminations. There are two ends to every conductor that will require attention. Read instructions for the equipment to which terminations will be made. Your limiting factors may be on one of the two ends of the conductor but will apply to both.
Proper torque when terminating conductors is one step to prevent problems at these locations within the power distribution system. In addition to preventing heat, it’s a step to ensure the hold on conductors during fault events where high short circuit currents flow imposing strong magnetic forces that could pull these conductors from their terminal. NEC Section 110.14(D), titled "Installation,” requires proper torque through the use of calibrated torque tools for terminations where the manufacturer has provided specific instructions and torque values.
The challenge of this topic is the verification of torque after the fact. We have to be careful that we don’t over torque by continuously tightening lugs after the installation. Light can be shed on how to address this situation in some sections of NFPA 70B, “Recommended Practice for Electrical Equipment Maintenance.” It is Section 8.11 that provides some guidance in this area. Section 8.11 of this document is titled “Thread Connections and Terminations,” and it speaks to terminations at initial installation and after initial installation. Initial installation use of proper tools and following instructions would appear to be straightforward. After installation is where we are left wondering how to properly address. NFPA 70B speaks to verifying proper tightness after the initial installation. It speaks to the process when there are signs of degradation and when there are no signs of degradation. When there are no signs of degradation, the following process is recommended by this document:
- Use a calibrated torque measuring tool.
- Set the torque tool to 90 percent of the specified torque value.
- If the screw or bolt does not move at this torque value, we can consider the connection properly torqued.
- If the screw or bolt moves, it is an indication that the connection or termination is not properly torqued.
- If the screw or bolt is not properly torqued, then the installation should be reinstalled. That means the wire is removed from the lug. Then inspect the conductors, possibly cutting off the existing, which would expose a new portion of the wire, and then reinstall on the termination.
Many will struggle with understanding how to handle checking an existing installation when it comes to torque. NFPA 70B is a good industry recommended practice that can help through this process.
CODES AND STANDARDS
Proper terminations are important and references exist to help address these tasks safely. The following National Fire Protection Association (NFPA) sections are a great place to start:
NFPA 70 Section 110.3(B), “Installation and Use”: A reminder that listed or labeled equipment shall be installed and used in accordance with the instructions included in the listing or labeling.
NFPA 70 NEC Section 110.11, “Deteriorating Agents”: Proper application of products recognizing that external sources can have a deteriorating effect on conductors and/or equipment.
NFPA 70 Section 110.12, “Mechanical execution of work”: Neatness counts and in terminations it can make a world of difference.
NFPA 70 Section 110.12(B), “Integrity of Electrical Equipment and Connections”: Covers protection from contamination from paint or other foreign materials.
NFPA 70 Section 110.14, “Electrical Connections”: Dissimilar metals, fine-stranded conductors, and necessary termination details and more.
NFPA 70B Section 8.11, “Threaded Connections and Terminations”: Provides guidance on addressing threaded connections and terminations, specifically torque.
NFPA 70B Section 16.4, “Bus Bar, Wiring, and Terminal Connections”: Speaks to loose connections and reminds us that proper torque is a function of bolt size, bolt type, terminal material, washer type, and type of bus bar.
There are many more sections in the Code that are important to effective terminations, but the above can get you started. Knowing the Code and continuing to study it as it changes will help in your effort to pay attention to the details.
The following UL category codes can help find information that is necessary to apply products.
AALZ: Electrical Equipment for Use in Ordinary Locations
ZMOW: Wire-Connector Adapters
ZMVV: Wire Connectors and Soldering Lugs
ZMWQ: Sealed Wire-Connector Systems
The following UL standards are of most importance:
UL 486A: “Wre Connectors and Soldering Lugs for Use With Copper Conductors”
UL 486B: “Wire Connectors for Use With Aluminum Conductors”
UL 486C: “Splicing Wiring Connectors”
UL 486D: “Sealed Wire Connector Systems”
UL 486E: “Equipment Wiring Terminals for Use With Aluminum and/or Copper Conductors”
Care should be taken when making terminations. Often, this work is left to the most inexperienced of the team. These individuals must understand how important their task at hand is and understand the code requirements that directly pertain to their work.
As always, keep safety at the top of your list and ensure you and those around you live to see another day.
Thomas Domitrovich, P.E., is VP of Technical Sales for Eaton’s Bussmann business within the Circuit Protection Division of Eaton Corporation. Thomas is based out of St. Louis, MO, and has more than 25 years of experience as an Electrical Engineer. He is a LEED Accredited Professional and a licensed Professional Engineer in the state of Pennsylvania. Thomas is active in various trade organizations including the Independent Electrical Contractors (IEC), International Association of Electrical Inspectors (IAEI), Institute of Electrical and Electronic Engineers (IEEE), National Electrical Manufacturer’s Association (NEMA), and the National Fire Protection Association (NFPA). Thomas is Principle member on Code Making Panel 2 for the National Electrical Code (NFPA 70) and an Alternate member on NFPA 73 for electrical inspections of existing dwelling units, both representing NEMA.