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August 10, 2006 A Prism Business Media Publication Vol. II No. 15



CONTENTS
Introducing the EC&M
E-Tradeshow


Maintaining the Motor Environment, Part Four

Electrical Troubleshooting Quiz

Replacing Explosion-Proof Motors

NEC at the Facility

The Practical Implications of OSHA

Answer to Electrical Troubleshooting Quiz



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About This Newsletter
This twice-a-month
e-newsletter is brought to you from the publisher of EC&M magazine.

MRO Insider addresses topics such as:

  • Working with management and supervision
  • National Electrical Code® on the production floor
  • Safety procedures and programs
  • Troubleshooting techniques
  • Equipment maintenance and testing tips
  • Managing motors and generators
  • Trends in training and education
  • Managing energy use


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    EC&M E-Tradeshow
    Introducing the EC&M
    E-Tradeshow

    EC&M magazine's new online tradeshow and conference series is now open! Use it as often as you like at no cost to you. The E-tradeshow is a 3D exhibition where you can examine some of the latest in electrical products, meet with exhibitors, and gather information. Plus, you'll be able to attend conference seminars inside the E-Tradeshow throughout the year.

    Just click here and you'll be connected to detailed information about how to get inside and make full use of the E-tradeshow. In minutes you'll be exploring in the 3D environment, be visiting in our charter exhibitors' booths, and checking out some very cool products.

    See you in the show!



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    Maintenance
    Maintaining the Motor
    Environment, Part Four

    "Shake, Rattle, and Roll" was great for Bill Haley and the Comets. But if you want your motor to rock around the clock, you must pay attention to what it's sitting on and how it's fastened in place.
    • Industrial motors may be face-mounted or foot-mounted. In either case, torque the motor mounting bolts per the motor spec sheet. Store this torque spec in the repair instructions, not in your maintenance procedures.
    • "Retorquing" properly tightened bolts reduces their clamping power because it results in overtightening. With motors, it also distorts the mounting flange (face-mounted) or feet (foot-mounted).
    • Use a fastener marking product to visually indicate where a bolt and nut align when initially torqued to spec. During normal preventive maintenance, you merely need to look at this marking to see if the bolts are still tight. If the line is broken, disassemble, replace the lockwashers, and re-assemble. Don't re-use split-ring lockwashers, as they lose significant spring tension with each use.
    • Typically, a foot-mounted motor bolts to an adjustable (e.g., slotted) metal base. A base with a long service life may be experiencing metal fatigue -- and consequently flexing when it shouldn't. This may be the source of "mysterious" vibration.
    • The base bolts to a cement pedestal (similar to the way a house bolts to its cement foundation). The pedestal can crack, so inspect for this.
    • Consider the pedestal part of the motor system. When doing alignment, don't assume it never moves. Over time, the normal shifting and settling of the building can move the pedestal and cause misalignment.
    • If mounting hardware fails, the base may shift on the pedestal, or the motor may shift on the base. Follow the mounting hardware tips outlined above.
    • Monitor for vibration to detect early misalignment. With large motors, misalignment can progress rapidly into catastrophic destruction.
    • If you encounter recurrent cases of excess vibration with the same motor, you probably have an inadequate pedestal or base. If you're unfamiliar with how to properly size and construct these, outsource the work to a qualified firm. This will save time and money, while averting downtime.


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    Repair
    Electrical Troubleshooting Quiz
    Even after three laser alignments, a motor continues to exceed vibration limits. What is the most likely cause? Or is there just one?

    The answer to this question appears at the end of this newsletter.


    Replacing Explosion-Proof Motors
    You may have a hard time finding an exact replacement for an explosion-proof motor. In many cases, machine builders use a limited production motor -- rather than one you're likely to find in stock. So you must order a replacement, having it built to the original specifications and then certified.

    But what if an explosion-proof motor fails on a critical production line, you have no spare, and there's a five-week lead time on getting a certified replacement?

    You know a motor shop that can build (and document) a replacement to the OEM specs in less than 24 hours. They work with explosion-proof motors all the time, but they aren't a factory-authorized repair center -- so they can't certify that particular motor.

    From an engineering standpoint, there is nothing wrong with using that uncertified motor. But there are those pesky legal issues....

    You must pass this risk management decision up through the chain of command; it's not one you can make. Management may decide to use the uncertified motor until you obtain and install a certified motor. Be careful to provide a complete picture of the issue, so the decision is senior management's -- not yours.


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    Operation
    NEC at the Facility
    Article 300 applies to all of the wiring in your facility. Part I addresses wiring 600V or under, and Part II addresses wiring over 600V. Article 300 violations are fairly common. Just as an example, have you ever seen public address (PA) system wiring draped over raceway? This installation violates 300.11(B). If you were to inspect a given area of your facility for Art. 300 violations, you might be surprised at how many you find.


    The Practical Implications of OSHA
    The Code of Federal Regulations contains 29CFR, which is where OSHA regulations reside. And it's massive -- 29CFR contains dozens of Parts, such as 29CFR1901 or 29CFR1990. Those last four digits are not date stamps -- they are just how the Parts are numbered. The Parts break down into Subparts. Part 1926, interestingly enough, has 26 Subparts (A -- Z).

    You don't need to know all of these regulations, but you do need to know, understand, and conform to your company's written safety plan. Your company is responsible for ensuring this plan satisfies OSHA requirements. You are responsible for following that plan.

    Even a company safety plan can seem intimidating, and all of us are subject to forgetting things. One helpful technique is to schedule two recurring appointments (e.g., every Tuesday morning, every Thursday afternoon) just for reading from the company safety manual. Bookmark where you left off, and pick up again there on the next appointment. You may spend only 20 minutes a week reading tidbits, but the combination of frequency and focus will make you an expert.


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    Quiz Answers
    Answer to Electrical Troubleshooting Quiz
    There is more than one likely cause. We've already addressed problems with the base and pedestal, so you know to check for those. But you want to avoid going through the expense of upsizing these, only to discover that didn't solve your vibration problem. Assuming alignment checks out, here are some things to look at before looking for pedestal and base problems:
    • Motor mounting. "Soft foot" is the most common cause. If you look carefully at the feet, you'll see distortion, due to overtightening. Replace the mounting hardware and torque properly to solve this problem.
    • Motor shaft. Use a dial indicator to check for shaft runout.
    • Motor bearings. Motor in-place testing for bearing problems is not always conclusive. Ask a motor shop for advice for your particular installation.
    • Power. Power anomalies between phases may be driving the motor into vibration. Use a power analyzer to see what you have.
    • Load. If possible, turn the load with portable turning gear and check for runout with a dial indicator. Also look at load mounting devices.


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