EC&M's MRO Insider

Getting Torqued Up

One great way to help ensure smooth operation and continual uptime in many production processes is the use of torque monitoring. Implementation can be as simple as a single torque limit switch that trips a local alarm (for example, to let the operator know to clear a jam). A more complex system might include a low torque shutoff switch, high torque cutoff switch, and analog torque sensor tied to a process control system. A low torque switch may indicate, for example, a broken coupling. In a sheet-fed system, it might indicate the sheet ran out. A high torque switch typically indicates a load problem, such as a jam in a grinder.

Analog monitoring allows you to do all kinds of things with trends. Maintenance-required conditions can produce a trend change. A quick corrective response between production runs often eliminates production downtime for those conditions. Some examples include:

• Sheet feed alignment is moving out of spec.
• Gearbox (multiplies torque) is malfunctioning (due to lubrication, coupling problems, alignment stray).
• Boxes are jamming together due to a conveyor roller problem.

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Electrical Troubleshooting Quiz

Maintenance is buying too many of a particular circuit board as a replacement part. During your initial fact-finding, you discover the following:

• The four main production lines each use this board in six places.
• About 90% of the failures occur in the same two particular places in each line.
• At each cabinet using this board, the 120V supply power waveform is severely distorted.
• At one line, you measure 2,917 ft of wire run to its supply panel.
• Each cabinet is grounded per the manufacturer's installation manual.

Visit EC&M's website to see the answer.

When Circuit Boards are Toast, Part 6

A power analyzer can help you stop the circuit board smoking problem. Severe waveform distortion in the incoming AC power supply to the cabinet can produce an unhealthy environment for circuit boards. So, you need to assess that power.

With the power analyzer, view the waveform. Some distortion is OK; power supplies can handle it. But if the distortion is severe and/or the waveform is flat-topped, a high harmonic load is interacting with the supply power (or possibly many harmonic loads on several branch circuits are).

The distortion is related to "source impedance," which is basically the opposition to current flow between this point of use (the cabinet) and the supply transformer.

To read more on this story, visit EC&M's website.

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NEC in the Facility

Commonly misunderstood/misapplied terms, part 2.

• AHJ (Authority Having Jurisdiction). Contrary to a widely held misperception, the AHJ may be someone other than the electrical inspector (who perhaps hasn't set foot in your facility since it was built). In fact, your facility may have multiple AHJs, any one of which can shut it down. For example, your insurer's representative inspects your facility and finds problems. If your facility doesn't meet certain requirements within a specified time, it won't be insured while operating. If your company leases its building, the owner is also an AHJ.
• Building. The NEC often says, "…building or structure." What's the difference? A building is a type of structure, but a structure is not a type of building. A building stands alone, or it's cut off from adjacent structures by fire walls (with all openings protected by approved fire doors).
• Conduit. Conduit is an enclosed wiring method, but not all enclosed wiring methods are conduit. Electrometallic tubing (EMT) is often erroneously called conduit. If you look in Chapter 3, you'll find various wiring methods — each with its own article.
• Conduit body. Interestingly enough, not just conduit systems have conduit bodies; so do tubing systems (e.g., EMT).

Safety

The Hazard Communication Standard (HCS) requires the manufacturer of a hazardous material to conduct a hazard evaluation of that material before selling it. HCS also requires your employer to conduct a hazard evaluation before permitting the use of that material by its employees or on its premises. But did you know the HCS also requires you to conduct hazard evaluation before using a hazardous material? It's easier than it may sound.

Begin the evaluation by reading manufacturer-supplied product hazard information. You'll find this on product labels and the Material Safety Data Sheet (MSDS) for that product. While HCS requires your employer to obtain the MSDS and make it accessible to you, things don't always go according to plan or regulations. If you make the effort but can't obtain the MSDS, have you satisfied the HCS requirements? The answer to that question is it's the wrong question. Only you can ensure your safety. Contact the manufacturer for a replacement MSDS.