At a medium-sized manufacturing plant, Carl (a mechanical maintenance supervisor) was promoted to the newly created position of maintenance manager (reporting to the plant engineer). The goal was to better streamline and coordinate maintenance activities.

Under the old system, each maintenance supervisor kept a file of maintenance procedures. Each was also responsible for a particular area of the plant. Nobody was responsible for electrical infrastructure, so electrical infrastructure didn’t get maintenance as a system. There wasn’t even an electrical department, only electricians assigned to each maintenance supervisor.

However, Carl decided to collect all the maintenance procedures and from them create a central system. In going through these, he found one he hadn’t seen before. It was titled “Power Quality Testing,” and it sounded important. He assigned it to the next available electrician, Jared, who was about one year out of vocational training.

Jared completed as much of the procedure as he was able to and reported to Carl that things didn’t look good so far. One of the tasks involved measuring the voltage between various points and ground, recording any values greater than 3V. Jared measured as much as 40V, telling Carl, “I used the building steel as my ground, you can’t get any better than that!”

Carl contacted your electrical services firm, and your boss assigned the project to you. How might you determine what’s wrong?

Modify power testing procedure

One thing we know is ground was not defined in the procedure, otherwise Jared would not have used the building steel as ground. You will find the definition of ground in Art. 100: the earth. Building steel is not the earth, so Jared used the wrong reference point. However, this is not the core problem. The core problem is the fact the procedure refers to ground rather than to the equipment grounding conductor (EGC).

Carl had not seen this procedure before because it was discarded; there’s no way to make sense of the data, so using it is pointless. However, this procedure can and should be modified to provide useful data. Its author probably was trying to ensure an equipotential plane between noncurrent-carrying metallic objects.

Checking EGCs as part of routine maintenance is overkill for the typical plant. Carl could put this checking into a work order if there are known power quality problems or other issues that may be attributed to a continuity break in the EGC.

What kind of break are we talking about? A common practice is to use metallic raceway as the EGC since three commonly used types of metallic raceway are listed in 250.118(2), (3), and (4) as permissible types of EGC.

The EGC can be compromised if assembled incorrectly. With tubing, the collar screw might not have been turned far enough to create the little dimple holding it in place. With conduit, perhaps someone used a nonmetallic coupling in a misguided attempt to prevent vibration transmission. Because metallic raceway doesn’t “go bad” the way, say, conductor insulation does over time, there isn’t normally a need to take readings to determine the condition or continuity of the raceway. A visual inspection of the couplings should suffice.

Similarly, the efficacy of bonding jumpers can normally be determined by a visual inspection; if no corrosion or other gross damage exists, it’s probably good to go. Including the bonding jumper connections in the thermography inspection program is a good idea. What’s not a good idea is to include a preventive maintenance task calling for tightening the connections.

Once any bolted connection is made, never put a wrench to it again unless you need to replace the connection. For example, suppose thermographic inspection shows a connection as a hot spot. If a subsequent conductance test across it shows bad, do you tighten it? No. You dissemble it and clean all mating surfaces. Then you replace the bolt, washer, locking device, and nut with new ones. You torque this connection to the recommended value, and it’s done.

That connection should last for the rest of your career at the plant unless some action on the connection mechanically damages it — such as a maintenance tech tightening it.

If Carl has reason to be concerned about power quality, the next logical step is to commission a qualified firm to conduct a power quality audit. A bigger concern, however, is the patchwork of maintenance on the electrical infrastructure. Carl needs to contact a qualified electrical testing firm to develop a proposal to address this.