Fluke - Why you care: mixed cabinet electronics and power

Our thanks to Fluke for allowing us to reprint the following article.

Mixing higher voltage 480- volt three-phase cables in the same cabinet as lower voltage 24- or 120-volt control wiring and communication cabling can result in erratic operation or even complete failure of electronic equipment inside the cabinet. Knowing what is inside the cabinet before you open it, the specific wiring issues to look for once inside, what values to measure, and simple ways to correct problems can help alleviate many erratic and sometimes "mysterious" control and communication issues on the plant floor.

Cabinets on the plant floor are often designed as a central control point for automation and process control equipment. Inside the cabinet are the electronic programmable controllers (PLCs), variable frequency drives (VFDs), and their associated communication and control wiring.

Since the equipment being controlled in the facility is typically 480 volts, the 480-volt three-phase power must often be routed through the same cabinet as the electronic controls-an advantage for both troubleshooting and maintenance. You can use the same cabinet to observe the indicator lights on a programmable controller, measure three-phase voltage on a motor starter, or adjust the drive...

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