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Electrical Troubleshooting Quiz - March 21, 2017

March 21, 2017
How to decide on what electrical testing is needed to quickly zero in on the cause.

You’ve been brought in as a consultant to help a plant get a handle on its many downtime issues. The plant long ago had staff cuts and there’s not much technical depth in the maintenance department. This point is driven home when you discover their most sophisticated piece of test equipment is a digital multimeter (DMM). So your first job is to characterize the types of failures and then decide on what electrical testing is needed to quickly zero in on the cause.

Fortunately, the plant does have a computerized maintenance management system (CMMS) and uses it. The maintenance manager generates a report that indicates most of the failures are corrected by replacing electronic circuit boards. What testing do you recommend?

This looks like a power quality problem, specifically a problem with voltage spikes. The most likely source is a large motor starting across the line.

Get a list of the largest motors. Then see if those DMMs have high/low recording and if you can use one on each large motor to monitor the supply voltage. The spikes may be of sufficient duration for the DMMs to capture them, but try to get the plant to at least rent a power analyzer. The plant could have other loads generating spikes, for example a robotic welder. Look at those, too. Another possibility is flashover due to improper bonding.

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