Bringing anomalies to light with IR inspection
Use infrared inspection to determine thermal patterns of electrical systems.
By James Brady, Brady Infrared Inspections
- Infrared technology is a powerful tool that can be used to detect thermal anomalies in electrical systems.
- Throughout the evolution of infrared technology for predictive maintenance applications, electrical system inspections have remained the cornerstone of the industry.
- Learning to recognize the significance of abnormal heating and the ramifications it has on the operation of an electrical system legitimizes the use of infrared technology and solidifies the role of an infrared thermographer as a key player in the electrical maintenance industry.
Infraspection Institute will host IR/INFO, a unique gathering of thermographers, engineers, technicians, and managers involved in P/PM or NDT technology to exchange information on infrared technology, on Jan. 13-16 in Orlando, Florida. For more information or to register, visit http://www.infraspection.com/IRINFO_Orlando
Throughout the evolution of infrared technology for predictive maintenance applications, electrical system inspections have remained the cornerstone of the industry. Despite being somewhat overshadowed in recent years by building science applications, the demand for infrared inspections of electrical systems remains high. Accurate diagnosis begins with understanding electricity and what causes thermal anomalies. Several types of defects, including those associated with compromised connections, overload conditions, load imbalances, harmonics problems, and inductive heating, may be encountered during an infrared inspection.
Electricity, current, and heat
Electricity is energy made available by the flow of electric charge through a conductor. It travels at different potentials that are measured in Volts. Common voltage classes include 120/208 V and 277/480 V. In most of these settings, the wiring is specified as having three hot legs commonly termed A-, B- and C-phase, and a neutral leg, although exceptions occur where three hot legs are present in places where motors are the load device.
Figure 1. Voltage classes obtain their values by the potential that exists between each phase and between each phase and neutral and/or ground. The same principles apply to other voltage class systems.
Voltage classes obtain their values by the potential that exists between each phase and between each phase and neutral and/or ground. For example in a 120/208 voltage class system, 120 V is measured between the neutral wire and one of the hot phases. In the same system, 208 V of potential exists between each of the hot legs (Figure 1). The same principles would apply for a voltage class of 277/480 V and others.
The flow of current is necessary in an electric system for infrared to be an effective diagnostic tool. Current is measured in Amperes and is defined as the movement or flow of electrically charged particles through a conductor. As charged particles flow through a conductor, they interact with one another to generate heat that is detectable with an infrared camera. The National Electric Code specifies conductor sizes for specific current flow so that excessive heat does not persist under specified load conditions. In correctly designed electrical systems, the heat generated by circuit load should fall within published standards for absolute maximum allowable temperature criteria.
Where current flow exceeds the design capacity of a conductor, a higher concentration of current flow is created for a given area of conductor, and it in turn generates heat. The amount of current flow and severity of resistance will dictate the amount of heat generated.
Ammeter and temperature comparison
An infrared camera can decipher thermal patterns associated with circuit load; however, it is not able to determine the amount of load on a circuit. An ammeter provides this information to the thermographer and allows the comparison of temperatures of different components under similar/identical loads. For example, 10 A of current flowing through a #12 wire on one circuit should be the same temperature as 10 A of current flowing through a #12 wire on an adjacent circuit, assuming they are operating in the same ambient temperature. If there is a deviation from this, it may suggest an abnormal condition that requires further investigation.
When using an ammeter, it is not always possible to locate another circuit with similar load conditions. If this is the case, the same circuit under question can be used to compare a temperature against itself. This is done by measuring the load-side conductor temperature to the line-side conductor temperature to obtain a delta temperature. This method is particularly useful when looking at single pole breakers. Measure the temperature of the problem area against the temperature of the wire conductor some distance away from the problem to get a reference temperature. Using this method assures that temperatures are referenced on components under identical loads.