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Vol. VII No. 14
Indirect Maintenance, Part 1
Electrical Troubleshooting Quiz
When Circuit Boards are Toast, Part 7
NEC in the Facility
Safety
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Maintenance

Indirect Maintenance, Part 1

The standard perception of motor maintenance is that it involves work on the motor. However, this perception is incomplete. Why? Because power quality problems destroy thousands of motors each year. Motors suffer from harmonics, low voltage, voltage imbalances, and other maladies that result from poor power distribution system design and maintenance.

But why are motors special victims of power quality problems? Why do motor failure rates rise faster than failure rates of other equipment as power quality problems get worse? We can sum it up as "windings and bearings."

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

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Repair

Electrical Troubleshooting Quiz

Various issues keep arising with mysterious causes. For example:

  • A supervisor keeps finding empty boxes stacked up in front of a fire exit, but nobody saw who did it.
  • During the monthly fire suppression system inspection, the inspecting tech found the supply valves had been shut off.
  • During the PM on a critical production line, the tech found a jumper installed around an e-stop.
Each of these incidents puts people at risk for injury or even death. Obviously, your company's insurer would not be happy either. What can you do, electrically, to reduce the mystery level?

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

When Circuit Boards are Toast, Part 7

In the cabinet where your circuit boards have been turning to toast, do you have a receptacle fed from the same panel that supplies the electronics in that cabinet? If so, this allows you to check the panel that supplies the cabinet without having to remove the panel cover (or even find the panel).

Take these two voltage measurements: line-to-neutral (L-N) and neutral-to-ground (N-G).

A low L-N voltage could be due to:

  • Voltage drop (conductors are too small for the length of run).
  • Voltage loss (for example, through poor connections).
  • Overloaded branch circuit.
  • Low panel voltage.
  • Any combination of the above.
The N-G measurement can help you sort this out. The hot and neutral conductors have impedance and current, which is why you have voltage drop. If these conductors are the same length and size, the voltage drop on them is the same. If you have a drop of 1V on each conductor, then for a 120V supply you’ll have 118V at the receptacle.

Assuming your system is correctly wired and bonded, you'll see the other 2V on L-G. Why? Because current doesn't (normally) flow in the ground conductor, it has no voltage drop. This means it acts like an extended test lead from your DMM to the N-G bond.

In Part 8, we'll see why this is useful.

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Operation

NEC in the Facility

Commonly misunderstood/misapplied terms, Part 3.

Did you know there’s no such thing as a wirenut? What people usually mean by this misuse of a trade name is a twist-on pressure connector. Other commonly misused terms include:

  • Cutout box. This is a specific kind of enclosure. First of all, it's surface-mounted. A box that isn't designed for surface mounting isn't a cutout box. A cutout box also has swinging doors (or covers) secured directly to the walls of the box, and these doors (or covers) telescope with the walls of the box.
  • Dead front. This doesn't mean the front has no door. It means a person on the operating side of the equipment isn't exposed to live parts.
  • Dust-tight. A dust-tight enclosure may not be suitable for a high dust area. Why is this? The term means dust will not enter under specified test conditions. It doesn't mean dust absolutely cannot enter. You may need something beyond dust-tight to meet the Chapter 5 (Special Occupancies) requirements of your particular application.
  • Duty. Intermittent, periodic, short-time, and varying are all specific types of noncontinuous duty. Each has its own definition. This matters, especially when dealing with motors or utilization factor.

Safety

In today's economy, companies want to maximize the ROI of resources. Consequently, maintenance departments are being tasked with more non-maintenance activities and project work. This can prove costly. Simply working through fatigue may appear to save money in the short run, but its costs include lower productivity, higher error rates, and higher accident rates.

You can raise productivity through technology. Test equipment upgrades can speed up troubleshooting, PdM, and PM. So can monitors (e.g., power, battery, vibration).

Another issue is floor space. Where you realistically need 40 in. of working clearance, some production manager says 3 ft is all you get. He then paints a line at 2 ft, 11 in. and moves production equipment right up to the line. But the OSHA and NEC clearances are, according to OSHA and the NEC, bare minimums. Work out exactly why a given spacing is required [110.26], and document that.

Don't permit equipment rooms to be used as storage areas, either.

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