When relay contacts are used to switch inductive loads, such as auxiliary relays or solenoids, extremely large voltage spikes can be generated when the relay contact opens, these large spikes can cause pitting of the relay's contacts, thereby reducing its usable life.
The internal functioning components of an electronic instrument operate on a low DC voltage, generally 5V, and respond to signals as low as 1V or less. In contrast, stray voltage spikes in excess of 100V and sometimes thousands of volts can be detected in the industrial environment. These voltage spikes can be coupled from power lines that are powering equipment that contains S.C.R. circuitry, or in other ways causes rapid load changes on the AC line. These spikes can also be coupled from lines that are actuating AC or DC solenoids or actuators. In other words, any wiring in an industrial application should be considered a potential noise source.
For more information regarding our EMI Installation Guidelines, download the following .PDF document.