Electrical Troubleshooting Quiz

The plant air system has shut down in the middle of a critical production run three times in the past month. Each time, a blown fuse had to be replaced. Because each interruption ruins the run and requires 2 hr of cleanup before production can resume, the plant manager wants you to determine what’s going on and fix it.

One fuse was inside the compressor control panel, another at the motor disconnect, and the third at the feeder panel. Are these problems related? How can you troubleshoot this situation?

These events probably are related. One reason fuses fail is because they sacrifice themselves to protect conductors and equipment. Common causes may include:

• Power anomalies. Begin with a power analyzer on the compressor supply, and see what it shows through several cycles of operation. Don’t fixate on harmonics. Voltage imbalance coinciding with the motor starts, for example, can be causing fuses to blow.
• Bonding errors. With improper bonding, you can easily build up potential that is eventually released via flashover between metal parts. If you’re injecting 1,000V spikes into your control wiring, fuses will blow.
• Wrong fuse type. Capture air compressor inrush current on a power analyzer, and you’ll see why compressors typically use dual-element time-delay fuses.

When fuses are failing frequently or “at the worst possible time,” the cause is probably poor maintenance of the fuse systems. At the very least, maintenance should include infrared scans, visual inspections, cleaning, and clip tension assessment.