Surge Suppression

Have you checked your grounding? You will hear this first question when calling tech support with an intermittent drive or controller problem. This question serves two purposes. 1-Perhaps the grounding is bad. 2-It provides time to look for the real answer.

The problem may be with surges introduced by other equipment. A pneumatic or hydraulic solenoid may be switched or a contactor or starter picked up. A simple surge suppressor on each solenoid and other coils may solve your intermittent problem. This applies only to coils switched with dry contacts, not solid-state PLC outputs.

Putting a suppressor across all coils switched with dry contacts is easily done and inexpensive. Many of these suppressors look like a shotgun shells with two outgoing leads.

The worst case of EMI interference in my career happened in a paper mill whenever a vacuum pump motor was started using old vacuum contacts in a high voltage circuit breaker. The interference was so bad, dozens of thyristors in drives over 3 paper machines would fail. Once we knew where the problem was coming from, it was easy to fix.

Over the past year working in a paper mill, I have inquired about the cause of damaging surges. Some reasons were improper switching sequences, applying power factor correcting capacitors, and vehicles crashing into sub-stations.