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Guidelines for Performing Infrared Inspections of Motor Control Centers

Whether it’s your first infrared inspection or you’re a veteran with hundreds of surveys under your belt, it’s important to realize that in order to successfully identify and analyze thermal anomalies, it is beneficial to understand the operation of the equipment under inspection. This paper will provide guidelines for performing infrared inspections of motor control centers, identifying key components and potential problem areas, illustrating both common and not-so-common thermal anomalies.

Figure 2: The bus stabs at the back of the MCC are where the incoming connections to the main horizontal bus occur. These are important IR inspection points and are often overlooked or misdiagnosed. The thermal image to the right reveals a hot spot indicating a potential problem.

 

A motor control center, or MCC, is a modular cabinet system for powering and controlling motors in a factory. MCCs are quite common in factories having heavy machinery. Typically, an MCC cabinet consists of a metal enclosure with doors providing access. Although the contents may vary, normally the MCC contains a motor starter, circuit breaker and possibly a power transformer. The MCC enclosure protects personnel from contact with current carrying devices, and it protects the components from various environmental conditions.

There are different classes and types of MCCs, but generally speaking, an MCC looks like a row of file cabinets with each cabinet representing an MCC section. The drawers of the file cabinet represent the plug-in units that contain the motor control components. Three phase power is distributed within the MCC by bus bars, large metal current carrying bars. The horizontal bus provides three-phase power distribution from the main power supply. Vertical bus in each section is connected from it to individual MCCs. Bracing and isolation barriers are provided to protect against fault conditions. The plug-in units of an MCC have power stabs on the back to allow it to be plugged into the vertical power bus bars of the structure.

Beginning Your MCC Infrared Inspection:
Before opening the panel or door on a motor controller, prescan the enclosure to assure a safe opening condition. If excessive heat appears on the surface of the door, extra care should be taken when opening it. The thermographer or escort may decide to note the condition as unacceptable and not take a chance on opening it under load. Once the unit is open, begin with both an infrared and a visual inspection to assure no dangerous conditions exist.

Read More! 
Download this white paper to learn more about the recommended guidelines for inspecting the motor control center (MCC). The paper describes how to identify key components and potential problem areas and illustrates both common and not-so-common thermal anomalies.

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