Machine Mounting

Frequently Asked Questions & Answers

Machine Mounting

Question:Does a machine’s mounting style affect its vibration?

Answer: Yes. When evaluating the vibration of electrical machines, it is important to understand the machine’s mounting because mounting and vibration are closely linked. Two passive (admit insignificant external disturbances to the machine) methods of mounting a motor are resilient mounting and rigid mounting. Following is a brief description of each, and an explanation of their affect on vibration.

Resilient Mounting: Resilient mounting entails suspending the machine on a spring, or mounting it on some type of elastic support (rubber, springs, etc.). Natural oscillation frequencies of the suspension system and machine should be less than 25 percent of the frequency corresponding to the lowest speed of the machine under test. The effective mass of the elastic support should be no greater than 10 percent of that of the machine, in order to reduce the influence of the mass and the moments of inertia of these parts on the vibration level.

Rigid Mounting: Rigid mounting entails fastening the machine directly to a relatively massive foundation. According to NEMA MG1-7.06, a relatively massive foundation is one that has a vibration which is limited, during testing, to 0.02 in/s peak (0.5 mm/s peak) above any background vibrations. The horizontal and vertical natural frequencies of the complete test arrangement shall not coincide within +10 percent of the rotational frequency of the machine, within +5 percent of two times the rotational frequency, or within +5 percent of one- and two- times the electrical-line frequency.

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