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February 28, 2012
Broken Breakers, Part 3
Electrical Troubleshooting Quiz
Replacing Cables, Part 6
NEC in the Facility
Safety

Maintenance


Broken Breakers, Part 3

Your maintenance procedure for circuit breakers should begin with inspection. That includes such things as:

  • Inspect breaker cubicle for signs of arcing or flash. Note any issues.
  • Visually examine conductors for discoloration and signs of insulation damage.
  • Look for signs of insect or rodent invasion in the surrounding panel.
  • Look for any broken parts, loose hardware (e.g., a bolt on the floor), and other signs of mechanical damage.
In addition, follow the manufacturer's guidelines for:
  • Testing and inspecting mechanical linkages and other components. Don't try to fix these; order replacements.
  • Cleaning mechanical components. The main issue here is to prevent actually spreading grime via improper cleaning.
  • Lubricating mechanical components. Use the specified lubricant, not whatever's handy. Mixing incompatible greases can easily destroy a $2,500 breaker. Apply only in the amounts and locations specified.
To read the earlier parts of this series, visit EC&M's website.
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Repair


Electrical Troubleshooting Quiz

A circuit protected by a 1,200A circuit breaker had reached the design maximum of 960A. With 20% headroom, no new loads were added. But with harmonics, power factor, and other contributing problems (e.g., poorly maintained mechanical gear boxes), the load crept up past 1,200A. The breaker didn't trip, but the power monitor triggered an alert. The alert allowed for time to fix several overload problems and schedule breaker maintenance. Wisely, you rented a breaker test kit and tested the breaker after maintenance. It performed flawlessly.

Due to a design oversight, the circuit recently acquired a total load of 1,250A, but the breaker didn't trip. What might be wrong?

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

Replacing Cables, Part 6

Let's say you selected the correct rope for the cable pull. Your electrical distributor told you that a 3/4-in. cable-pulling rope can handle 12.6 lb per 100 ft of pull and a 5/8-in. rope can handle 9.3 lb. Your calculations showed this pull would require about 9 lb, so you went with the larger rope just to add a safety factor.

To avoid shoulder strain, this pull was set up with a motorized take-up reel. The pull was going just fine, with the cable feeding smoothly into the raceway. Inexplicably, however, the cable suddenly slowed, and then the rope snapped.

Or was it inexplicable? This kind of scenario tends to occur when the cable spools and reels are taken for granted.

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

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Operation


NEC in the Facility

The list of potential arc-flash hazards in 110.16 isn't meant to be a checklist you can use to see where arc-flash hazard warnings aren't required. The listing of equipment emphasizes, rather than limits, applicability. An arc-flash warning must be posted for any electrical equipment if people might access it, even for a visual examination, while it's energized or if it's not in a dwelling unit.

The NEC doesn't detail the arc-flash safety requirements, and neither does OSHA. These are in NFPA-70E, as noted in Informational Note 1 in 110.16. The NEC is concerned only with the posting of warning signs. This requirement may go by the wayside someday, because it's now redundant with other measures required by NFPA-70E.

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

Safety

Where do you store those cans of gray spray paint you use for touching up enclosures? "On a bookshelf in the maintenance department" is the wrong answer. Sticking these containers in a box outside the door doesn't work either. The right answer is "We keep these in a special locker made just for small amounts of flammables. We put the white touch-up paint in there too, along with the solvent we use for cleaning busbars."

Be sure you know what that cabinet is designed to hold, though. If you don't have the original literature that came with the cabinet, go on the manufacturer's website. You should find the limitations in the sales information for each given cabinet product. If you don't see it, use the "Contact Us" or "Support" link to find the necessary information.

You need to know:

  • What you can actually put in that cabinet.
  • How much the cabinet can safely hold.
  • How to ventilate the cabinet location.
  • Applicable restrictions.
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