[en] As part of the NRC Nuclear Plant Aging Research Program (NPAR), an assessment was made of the characteristics of aging and service wear of motor control centers (MCCs). MCCs perform an important function in the operation and control of a large number of safety-related motors; thus, the operability and reliability of MCCs can impact the overall safety of nuclear plants. This report follows the NPAR strategy and investigates the operational performance, the design and manufacturing methods, and the current maintenance, surveillance and monitoring techniques of MCCs. A significant result described in this report concerns the identification of important MCC failure modes, causes, and mechanisms from plant operational experience. Frequencies of failure determined for the various subcomponents of MCCs also are described. In addition, recommendations are provided for functional indicators to monitor the performance of MCCs. 22 refs., 27 figs., 6 tabs