Mobile Friendly  Web Version  Add to Your Safe Sender List   Subscribe to EC&M August 9, 2011
Vol. VII No. 15
Indirect Maintenance, Part 2
Electrical Troubleshooting Quiz
When Circuit Boards are Toast, Part 8
NEC in the Facility
Safety
Advertisement

  EC&M's MRO Insider

Maintenance

Indirect Maintenance, Part 2

Previously, we said motors are special victims of power quality problems. It's also true that motors are special contributors of these problems. With their inrush currents, inductive load characteristics, and electronic drives (if not harmonics corrected and power factor corrected), motors place heavy burdens on a power distribution system. Even the physical connections require extra care and attention beyond that afforded to "normal" distribution system loads. This is why you can buy a roll of rubber "motor lead tape." How many other loads can you name that have a special lead tape named for them?

Article 430 ("the Motor Article") is the longest Article in the entire National Electrical Code, and yet other Articles of the Code still deal with motors. Part of the solution to that part of the motor maintenance puzzle dealing with the power distribution system is in Art. 430. If your motor supply doesn't conform with Art. 430, then you’re going to have a "high maintenance" situation. If you are in that situation, review Art. 430. You might just find that someone installed it improperly.

Advertisement
Get a grip on accuracy.
The Fluke 62 Mini non-contact thermometer is the perfect introduction to infrared (IR) thermometers for the professional. With the best accuracy in its class, the Fluke 62 Mini offers quick and reliable surface temperature readings. Rugged enough for industrial environments with its protective rubber “boot, the 62 Mini also comes with a handy nylon holster.

Repair

Electrical Troubleshooting Quiz

Over the past few years, equipment failure rates have been steadily rising, and you've been called in to find out why. The plant manager called you aside and told you:

  • All PMs have been done on schedule; no deferments.
  • The PM frequency on critical equipment has been doubled, but this didn't change the failure rate.
  • The PM procedures were all entered into the CMMS last September.
  • Each technician has a bound copy of the PM procedures.
  • Everyone in maintenance has been multi-craft trained.
What the plant manager does not talk about provides good clues. What might those be?

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

When Circuit Boards are Toast, Part 8

In Part 7, we started looking at the line-to-neutral (L-N) and neutral-to-ground (N-G) voltage measurements at a convenience receptacle in the cabinet where circuit boards were turning to toast. Why are these measurements useful?

As the circuit load increases, so does the current (per Ohm's Law). Voltage drop increases as current increases. So if a branch circuit is overloaded, voltage drop increases. Voltage drop is something you calculate based on circuit current and voltage, and conductor length and gage size.

Using a DMM, you can also measure the voltage drop. If your system is wired and bonded correctly (and connections are good), then your N-G measurement will be the voltage drop. Subtract this from your nominal voltage, and the result should match your L-N measurement. If it does not, you have current flowing in the ground conductor.

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

Advertisement
Baldor offers the broadest line of energy efficient industrial electric motors in the world. Fractional to 15,000 Hp, there's a Baldor Super-E® premium efficient motor for any need…any application. Visit our website and receive your free copy of EISA 2007 along with Baldor energy savings information.
Click Here

Operation

NEC in the Facility

Commonly misunderstood/misapplied terms, part 4.

Pop quiz: Do explosionproof enclosures protect components from explosions?

Answer: By "explosionproof," the NEC means the enclosure serves as a containment for the explosion. It confines an explosion to its inside rather than protects against one from the outside.

Some other commonly misunderstood terms include:

  • Fitting. A termination isn't a fitting. In a wiring system, a fitting primarily serves a mechanical function rather than an electrical one. A bushing is an example of a fitting. It may also serve an electrical function by preserving electrical continuity of metallic raceway.
  • Garage. It isn't necessarily a place where vehicles are stored. To be designated a garage, it merely needs the realistic potential of serving that purpose (or of being a place where vehicles are sold, rented, repair, exhibited, or demonstrated).
  • Ground. This term has been a source of confusion and friction in the NEC for decades. The NEC definition now is very simply "the earth." The NEC still occasionally uses "grounding" to mean "bonding," but that practice is giving way to this definition.
  • In sight from. This has more meaning than its words indicate. In NEC parlance, it is also 50 ft away or closer.

Safety

You use various chemicals in your work. Your supervisor's probably told you to read the label on a container before using what's in it. But if you've read the MSDS, why read the label? True, labels repeat what's in the MSDS. For example, a label may tell you what precautions to take when handling the material. However, the label will also tell you how to dispose of the very container you're holding in your hand.

Rock climbing is a sport that many people consider dangerous. To reduce the danger, safe climbers check their harness before each climb — even if they've already checked it multiple times. This redundant checking is one principle behind reading the label, even though you may have read the same information on the MSDS less than an hour ago.

What if a container doesn't have a label? Then don't use it! Even if you "know" what's in it, a mistake could prove fatal.

Advertisement


Advertisement


subscriber tools
 Subscribe  Unsubscribe  Change email address  Archives 
 Contact Us  Subscribe to EC&M