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Electrical Troubleshooting Quiz - February 7, 2017

Feb. 7, 2017
What to look for when one of two identical production lines fails and the other doesn't.

The plant has two identical production lines that were installed at the same time. They make heavy use of robotics and other automation, and thus contain quite a bit of electronics.

Line A has almost no problems — ever. Line B shuts down almost daily with some problem or another. The three most common failures are: dead circuit boards, drive motors with spun bearings, and dead servo motors.

Maintenance on these lines is identical, except on Line B a power analyzer has been installed at different points for a couple days at a time to locate power anomalies. Thus far there haven’t really been any. Line A reference readings are similar.

How might you solve this problem?

Probably, one crew installed Line A, and another Line B — and with a difference.

Raceway makes a great equipment grounding conductor (EGC), especially for electronics. Its large circumference compared to a solid conductor gives it more surface area on which high frequencies can travel. But if that metallic path is interrupted, you no longer have an EGC.

Take a look at where metallic raceway enters and leaves junction boxes and panels. If the EGC path relies on the locknut for continuity, you’ve likely found the cause of damaging circulating currents. Look on Line A and you should see a bonding jumper at each of these locations.

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