Electrical Troubleshooting Quiz — June 7, 2022

Early last year, the company brought a new plant manager (Richard) onboard following the retirement of his predecessor. Richard has a few obsessions that people snicker at. For example, he wanted every wastebasket on the production floor to be in a designated spot, so he had a circle for that purpose painted at each operator station.

When Richard said he hates vibration and wants it eliminated, the plant engineer was elated. Finally, there would be vibration monitoring on nearly every motor in the plant. Approval for some mechanical engineering projects also came through, allowing weak stress points to be strengthened. And the plant engineer could finally order the snubbers he wanted to try on Line 3. Unfortunately, Richard, who is not an engineer, insisted on some design “improvements” of his own.

Over the objections of the plant engineer, Richard had PVC couplings inserted into metal support structures to dampen vibration. Richard owned his own noise dosimeter and used this to take “before” readings for the pilot project. Sure enough, noise dosimeter readings taken immediately after the first such modification showed a noise reduction. This was all the proof he needed that he was right.

It wasn’t long before it seemed as if PVC was popping up in equipment support structures all over the plant. But vibration monitoring on the motors was showing an increase, not a decrease, in vibration. And the failure rate of motor bearings was going up. How can there be less noise but more vibration at the motors?

Nonconductive plastic

In automobile engines where the camshaft is located above the crankshaft but below the heads, such as in V-configuration engines (V6, V8), a timing chain is typically used to allow the crankshaft to drive the camshaft. In passenger cars, it’s typically coated with phenolic to reduce noise. In high-performance engines, there’s no plastic coating. The chain may be of the double-roller type, which is louder. Or the chain may be replaced by a gear set, which is louder still.

If you’ve ever heard one of these high-performance engines run, you’ve heard that whirring that many describe as sounding like a sewing machine. It’s something you have to accept in a race car, but not in a passenger car.

A typical passenger car engine redlines at about 5,500 revolutions per minute, but high-performance engines may redline at twice that speed. So, we have a quiet system that will shake apart at a much slower speed than a noisy system. The reason is that plastic is structurally weaker than steel. This is the dynamic at work in the plant.

The vibration monitors are showing this dynamic at work. What they are not showing is an additional dynamic, which is the interruption of the equipment grounding conductor. Introducing all that nonconductive plastic in place of low-impedance steel is causing undesirable current to flow through the bearings.

As the bearings degrade due to the undesirable current, the vibration also increases. So now there is vibration from two sources: weak structural material that is replacing sound energy (noise) with motion (vibration), and bearings that no longer provide the smooth ride to their loads that they are supposed to provide.

The plant engineer is the point of failure here. His job is not to merely implement the plant manager’s wishes but to ensure that engineering in the plant follows engineering principles and best practices. Vibration isolators are special-purpose devices that address both noise and vibration; their application follows a specific protocol.

Take ownership

The physical problems are mechanical engineering ones, but the effects are felt in the electrical area. The root problem is a management one, and the plant engineer needs to “manage up.” He should have nipped this whole thing in the bud by managing his boss, who had good intentions but did not have the background to know what he was doing.

To solve this, you’re going to have to “manage up” both the plant engineer and the plant manager. You can’t come at this from the vantage point of being an expert because you’re on the electrical side, not mechanical. You will need to use outside resources to show both of these people why PVC cannot be used in this way and what solutions can be implemented based on the physics and standard practices. You also have those vibration readings from which you can show the increase as each of the noise reduction projects has rolled out.

The plant manager will have to accept some noise and will need to understand why that is so. Be sure you document these “manage up” efforts in case something goes sideways.

You need to push the “undo” changes through so they happen quickly. Otherwise, motor failures will increase dramatically, and corporate will take notice. Or the PVC will fail dramatically, and someone will get hurt. The plant manager is not going to admit he messed things up; he’s going to protect his job for at least a quarter or two by scapegoating someone else — and that will probably be you. So take ownership. The facts are on your side; make sure you present them in a clear and nonblaming way.