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Occasionally technicians fail to replace the terminal box cover after installation or service work and this can result in things that cause compressor damage. Good practice would always dictate that the electrical connections be protected from dirt, moisture, or other items which might cause an electrical short and that the cover on securely so that it cannot land into the terminal box and cause an electrical short.
The trip point of an external protector is determined by the temperature of the protector sensing element, and this in turn is determined by the motor current, the temperature of the compressor body, and the temperature of the air surrounding the protector. If the terminal box cover is not in place, and especially if the protector is located in a moving air stream, its trip time may be greatly extended, and the reset time greatly shortened. Under such circumstances, the motor protection system is less effective, and motor failure during the starting cycle on PSC motors is quite possible.
Check out AE10-1187 to find out more – https://webapps.emerson.com/online-product-information/Publication/LaunchPDF?Index=aeb&PDF=ae1187.pdf