When performing a PQ investigation, lack of proper safety training and effective troubleshooting procedures spells trouble every time.
Most companies assume their electrical personnel are safety conscious. Yet, an informal poll of electrical maintenance personnel involved with power quality troubleshooting and other forms of electrical testing found almost all of them had violated safety rules on more than one occasion. Some of the respondents even experienced electrical shock incidents in the field as a result of their actions; without informing company personnel or seeking medical attention.
One of the most common complaints of electrical testing personnel is the pressure to complete the job as quickly as possible. This "hurried pace" usually leads to shortcuts, such as the omission of safety gloves and glasses, the improper use of test equipment, and the overriding of interlock switches.
A lack of technical expertise during a power quality investigation can also lead to trouble. In this age of "board-swapping" and software analysis, there's less emphasis on basic principles such as Ohm's and Kirchoff's laws. Another dangerous mindset is the continued adherence to the myth that current flows through the path of least resistance. Early last year, a test equipment manufacturer delivered a bogus statement in a product bulletin claiming it was acceptable to touch live, bare 480V terminations, provided it wasn't with both hands. It claimed AC current would only flow between the fingers and not the rest of the body.
Systematic test procedure
Another factor that leads to unsafe solutions is the lack of an effective troubleshooting procedure. An excellent source for establishing power quality investigation procedures is the IEEE Emerald Book (Std. 1100; Powering and Grounding Electronic Equipment). Chapter 6 (Site Surveys and Site Power Analyses) provides an effective troubleshooting procedure for most power quality problems. Additionally, some test equipment manufacturers have practical information in their applications manuals.
When performing a power quality investigation, remember these four levels of inspection:
- Contemplative. Before any investigation starts, know what the problem is, where it's located, what type of equipment is involved, and what type of test measurements are necessary.
- Visual. All good power quality investigators make a visual inspection of the equipment's integrity prior to making any measurement.
- Mechanical. If possible, a qualified electrical maintenance person should inspect and tighten all connections prior to making any metering measurements. There are two reasons for this. First, you should identify and correct any unsafe wiring conditions prior to metering. Second, the meters will not falsely identify a voltage quality problem that may actually be a loose connection on the circuit conductors or ground.
- Metering. To make this a safe and meaningful task, take your measurements after applying the first three levels of inspection.
Here's a list of common-sense rules for performing electrical measurements.
- Don't work alone. If you're working in pairs, make sure each of you knows what the other is doing at all times.
- Be sure to inspect all meter leads for damage. Also, check to make sure the meter is in good operating condition.
- Select the proper range and function for the test instrument.
- Make sure all equipment is properly grounded.
- Do not override interlock switches. These devices are in circuits for your protection.
- Remove all jewelry and loose-fitting clothing, including ties.
- Do not rush or cut corners when doing a survey.
To prevent accidents and obtain reliability during a power quality investigation, approach each site survey step-by-step, as if you were doing one for the first time. Remember, all the experience in the world means nothing if you don't perform the job safely.