Power quality can be negatively affected by such mundane factors as loose power connections.
When we consider all of the sophisticated apparatus used to improve the operational integrity of our sensitive equipment and systems, it seems absurd to talk about those common sense, "good housekeeping" practices.
Nevertheless, they are a valuable part of the power quality equation and require our attention. In fact, looking after our electrical environment can result in big dividends. Let's find out what's involved.
What is good housekeeping?
Most solutions to our so-called power quality related events have come from attending to little things around the shop. In almost every case involving a power quality investigation or site analysis, the first items that show up in need of correction are those in the area of wiring and grounding. These include "daisy-chaining" of neutrals and grounds, undersizing of ground wires (which are expected to carry electrical noise away from sensitive equipment), and even, believe or not, loose or missing connections.
The NEC and good housekeeping
We often hear a facility manager say, "One day, we're going to bring this facility up to the NEC." While this is an admirable goal and one that should be achieved, it reflects a major misconception: the NEC does not represent the peak of wiring and grounding methods and procedures. Instead, it reflects the minimum requirements needed to protect persons and property "from hazards arising from the use of electricity." In other words, the Code is a place to start in the battle for good wiring and grounding of sensitive equipment. But keep in mind, there is no substitute for, or compromise with, the provisions of the NEC.
In the context of power quality and the NEC, there are conflicting philosophies promoted by people with differing technical backgrounds and commercial interests. One controversy stems from the conflicting interpretations of the NEC's grounding requirements. While a safe operating power system is universally endorsed, some feel that required wiring practices interfere with the smooth operation of electronic systems. As such, they believe that you may have to install sensitive electrical and electronic equipment by "skirting" the provisions of the NEC. In fact, many equipment manufacturers, with warranty forfeiture threatened, direct the end user to do so.
This apparent conflict can only be settled by making safety the overriding concern, which is the intent of the NEC. If revisions have to be made for the system to operate properly, the equipment manufacturer must incorporate them in the equipment design, rather than asking for deviations from the NEC. In fact, when you wire with NEC safety provisions in place, satisfactory operation will not be sacrificed. The safest system will be the best operating one.
Good housekeeping is not just following the NEC, but includes all of the diligent, sensible practices taken during installation and maintenance. If more attention is given at the start of project to the important power quality implications, future problems will be headed off before they result in shutdowns or damage.
Where to get good housekeeping practices
You can get a feel for these practices by going through the FIPS (Federal Information Processing Standards) Pub 94, Guideline on Electrical Power for ADP Installations or the IEEE Standard 1100-1992, Recommended Practice for Powering and Grounding Sensitive Electronic Equipment (the Emerald Book).
The latter publication is especially useful in that it includes recommended design, installation, and maintenance practices for electrical power and grounding of sensitive electronic processing equipment used in commercial and industrial applications. These practices include both power- and signal-related noise control techniques.
In many instances, we are confronted with conflicting information and/or confusion in the power quality area, all stemming primarily from different viewpoints of the same problem. By referring to this consensus of recommended practices, the confusion and conflicting information is greatly diminished.
The Emerald Book addresses electronic equipment performance issues while maintaining a safe installation. A brief description of the power quality problem is usually given, along with possible solutions and the resources available for assistance in dealing with problems. Fundamental concepts are reviewed and instrumentation and procedures for conducting site power analysis are considered. Of special interest are the case histories provided to illustrate typical problems.
You can also follow case study discussions in a variety of publications. The case histories we discuss each month here are good examples.
Case history
Many times, we're involved with a consultant, contractor, or facility engineer who has not thought through the "hows" or "what-ifs" pertaining to wiring, grounding, or protecting a piece of sensitive equipment or its signal system. Thus, we are called in when this equipment doesn't work, or when there is no correlation to the errant behavior, or when the damage has already taken place. Thankfully, this is changing: more planning is being done using the new power quality guidelines.
One case study example comes to mind as a reminder to check our procedures for installing and maintaining our equipment, especially power conditioners used on computers or other sensitive loads.
A large telecommunications facility that manufactured digital electronic devices was experiencing a rapid increase in requests for UPS systems from operators in its software engineering area. This was the direct result of one of the workers asking to have a small electronic equipment system (4 to 6kVA) put on a self-contained battery supported UPS. (At the time, there were no other UPS needs apparent.) When this request was honored and a 10kVA UPS was provided for this application, the worker began to experience "clean power" - since this affected work area was now separated from the wiring problems in the rest of the software engineering area.
As the word spread among the other personnel in this department, more requests were made for small UPS systems, so many requests, in fact, that the facility manager had to put a stop to the separate ordering until it was determined why everyone needed a UPS! The answer from the workers was, "You're giving us bad power!" It was humorous, in a way, since the manager was being blamed for all theproblems, even though he had nothing to do with the power company delivering the energy.
The investigation into this problem led to some very disturbing housekeeping conditions on the UPS systems themselves.
Site investigation and solution
We were called in to do a site analysis at this facility and, in the course of the visit, we tested the output of one of these small UPS systems to determine its load characteristics. We were performing our examination with the load connected and in a nonintrusive fashion, or so we hoped.
Working at the floor level, we were suddenly covered by a " shadow" - someone was standing directly over us. It was a computer operator and she wanted to know what we had done to her computer! It was now "dead in the water", and she was suppose to go home in 30 min. Thanks to us, however, she now had a 6-hour recovery program to go through to retrieve the lost data! Needless to say, our credibility was suspect.
We re-checked the output of the UPS. All indicating lights showed good output, the voltage was correct, but no current was present. Then we went to the respective power outlet and found the same condition. The obvious theory: something was wrong between the UPS, which was running well, and the power outlet. The operator maintained, "It's you. Nothing else has happened except when you tampered with the system!"
We returned to the UPS output to prove that we had not changed anything and that the power was correct at the output. When we placed the voltmeter leads on the output to show her the voltage, one of the output wires moved sideways. Looking underneath the connection into the lug position, we saw that the outgoing wire had never been inserted under the lug. In fact, the lug had never been opened! The wire had simply been "jammed" up to make contact, and as long as you didn't touch the arrangement, it worked.
Now the worker was aware of the poor "housekeeping" that had caused the problem. The rest of the units were checked for the same problem, and better planning for installation and maintenance was instituted for the future.
In Part 2, we'll look at another example of a problem that began as an assumption about harmonics but really stemmed from poor wiring.
SUGGESTED READING
EC&M Books:
Practical Guide to Power Distribution Systems for Computers. Practical Guide to Quality Power for Sensitive Electronic Equipment. For ordering information, call 1-800-654-6776
Standards:
FIPS Pub 94, Guideline on Electrical Power for ADP Installations. For ordering information, contact the National Technical Information Service, U.S. Dept of Commerce, Springfield, VA 22161.
IEEE Standard 1100-1992, Recommended Practice for Powering and Grounding Sensitive Electronic Equipment (Emerald Book). For ordering information, call 1-800-678-IEEE.
EC&M Articles:
"New Power Quality Consensus Standard" February '93 issue. "There's More to Power Quality Than Meets the Eye" October '94 issue. For copies, call 913-967-1801.
RELATED ARTICLE: GOOD HOUSEKEEPING MEANS CHECK EVERYTHING - ASSUME NOTHING
The IEEE Emerald Book indicates that problems in industrial and commercial premises wiring and grounding account for a large share of all reported power quality problems. The greatest number of these is in the feeders and branch circuits serving the critical loads.
As such, the first activity in checking for power problems is to survey the soundness of the AC distribution and grounding system supplying the equipment. Problems here include such items as missing, improper, or poor quality connections in the power wiring and grounding from the source of power to the load. These problems can be generally classified as mechanical in nature.
Through error or oversight, intentional or unintentional, the power distribution and grounding system is not installed per national, state, or local electrical codes and other specifications. For example, the NEC only permits a neutral-to-ground bond at the source of power; that is, at the main panel or isolation transformer secondary. Yet, this improper connection is a common site in the field and is the source of many of the common power quality problems.
In new installations, connections may be left off or not properly tightened. Reversal of conductors also can occur. Connections may become loose because of equipment vibration. Even the ON-OFF cycling of a connected load, with its creation of cycled heating and cooling, can eventually result in high-impedance connections. Also, periodic additions or modifications to a distribution system may result in missing, improper, or poor quality connections.