Power Quality Safety

As I prepare to chair the next meeting of the NFPA 70B Recommended Practice for Electrical Equipment Maintenance committee, I reviewed some of the more significant changes made in the 2006 edition. Three key parts of any maintenance program are having a baseline to compare the results over time, forms for recording the necessary data to verify the proper operation and maintenance levels of such equipment, and a basis to determine what are the reliability expectations of the equipment.

To these ends, two new chapters were added in this latest revision that cover reliability-centered maintenance (with an annex filled with reliability and availability data on hundreds of pieces of equipment) and another chapter on starting an effective preventative maintenance program at the commissioning or acceptance testing stage to get baseline data for future comparisons.

The annex contains more than 30 maintenance forms as well as recommended maintenance schedules for various inspection and maintenance of everything from surge suppressors to medium-voltage circuit breakers.

But, one may argue the most important revision to the document was the creation of an entire chapter dedicated to personnel safety, right up in the front of the document before any of the maintenance tasks are described. The 70B document always dealt with safety, but the information was scattered throughout the document and it was difficult to get the full appreciation of the hazards involved.

The chapter is based on not only the previously included materials, but expanded to include the latest information from important sources such as NFPA 70E, Standard for Electrical Safety in the Workplace, and various appropriate Occupational Health and Safety Association (OSHA) safety documents, such as OSHA 1910 Subpart S and OSHA 1926 Subpart K. Whereas as the OSHA documents describes “what” to do to avoid electrical dangers, the 70E document goes into the “how,” with detailed lock-out/tag-out procedures and information on arc flash calculations, and the personal protective equipment (PPE) necessary based on the potential exposure to a given arc flash energy level. These are combined with the application to the maintenance of electrical equipment in 70B.

The beginning of the “Safety” chapter defines a “qualified person.” Knowing your limits is critical. People can be qualified for a variety of tasks and unqualified for others that would be necessary to complete an assignment.

The latter can be an overlooked aspect of safety. Letting someone do something in an unsafe manner, when you are qualified to determine such, is not only a significant safety issue, it is a legal (and moral) one. As 70B- states, “A person not qualified for a specific task, even though fully qualified in all other ways, should not be exposed to the hazard of that specific task.” Becoming qualified involves training, both formal classroom and on the job.

Establishing an electrical safe work condition includes six key steps from 70E Section 120.2, which are summarized in 70B Section 7.4.2. Though you should read those documents completely, the steps include things that may seem common sense, but have been the source of countless accidents, serious injuries and deaths. Determining all the possible sources of the electrical supply to the area being worked on goes well beyond throwing a single breaker labeled to cover such. Data centers can have triple redundant supplies that come on when one goes away.

In my own house, I turned the breaker off to change the outlet on a particular circuit, only to find that the previous owner had actually wired two different circuits together. Testing with a DVM prior to taking out the outlet is what saved an “incident” in that case, which goes along with another of the steps on “using an adequately rated voltage detector to test each phase conductor or circuit part to verify they are de-energized” [7.4.2 (5)], and not just phase-to-phase measurements but phase-to-ground as well.

In 70B, 70E and 29 CFR 1910.33, it is required that disconnecting means used to de-energize circuits and equipment on which work is to be performed be locked and tagged in the open position.

Another important section is that when the only alternative is to work on or near live parts, determining the degree of the personal protective equipment required should not be overlooked. Determining what degree of protection is needed involves knowledge of the arc flash hazard, with more details on that subject found in 70E and the IEEE 1584-2002 Guide for Arc Flash Calculations. Whereas 70B is a “recommended practice” for maintaining electrical equipment, 70E is a “standard” on creating an electrical safe workplace.

The subtle difference between a recommended practice and a standard are that the former cannot use the mandatory language of “shall,” but rather the somewhat toned down “should.” Safety is never a “should.” If it is not always a “shall,” you risk becoming a “was.” You just can’t get enough safety. EC

BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.


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