Power Quality Problems
Almost every power quality problem will be associated with a building-wiring problem. These include poor grounds, non-isolated circuits, and undersized conductors. Wiring practices adequate for traditional electric loads are often inadequate for sensitive electronic devices.Harmonics are higher frequencies mixed in with the base 60-cycle frequency. Harmonics are much lower in frequency than traditional noise. Harmonics are not random and occur at multiples of the 60-cycle base frequency. In addition, significant power can be involved with harmonics. Harmonics are usually created by power electronic devices such as variable-speed drives and battery chargers/rectifiers.
Voltage transients are very short-term spikes in voltage. Common causes are lightning and switching of inductive loads. Surges cause equipment damage.
Brief under-voltages and over-voltages, commonly called sags and swells, are closely related. The term “brief” means less than a few seconds. Anything longer than that is a long-term power problem.
Surge Protection Q&A
Q:What actually happens when a surge or spike reaches a protection device? How does the protection device handle it?A: A surge protector is designed to bond all the protected conductors together during a surge. This prevents a difference of voltage between conductors. When the conductors have the same voltage, there cannot be a current driven into the protected load. Surge protectors are not actually “blocking” devices, although some have series resistance that will slow a surge. A properly designed and installed suppressor should last indefinitely. Suppressors should seldom fail due to a surge.
Q: Is there a difference between a surge and a spike?
A: Technically, they are both the same. However, voltage sags, outages, and noise are commonly called “surges” by customers.
Q: Is there any agency that dictates ratings for surge protectors? Are there any special requirements when putting surge protectors in a UL-listed control panel?
A: UL tests packaged surge suppressors and lists them to standard 1449. The national electric code requires only UL-listed suppressors for power wiring. However, good engineering judgment should be used in any installation. Only fused suppressors should be used in electrical panels. The surge protector should be installed as close to the electrical panel as possible.
Q: What is the best way to protect electronic equipment from lightning?
A: First, install a well-grounded metal flagpole taller than the building in a parking lot away from the building. Second, use only quality surge protectors with two-stage design if possible. All metallic conductors entering the electronic equipment must have suppressors installed properly.
Q: What are the main specifications for surge protection devices? What should we be looking at between different devices to compare apples to apples?
A: We have found published specifications to be useless. Manufacturers publish almost anything that makes their product look good, and in fact, most cannot even verify the performance of their own products, or their published specifications.
For example, all suppressors are 1,000 times faster than they need to be. Quoting nanosecond or picosecond response time is ridiculous. Other useless specifications are surge energy rating (Joules), clamp voltage, “sine wave tracking,” etc.
One specification that has meaning is the trigger voltage of the suppressor. This is usually called the “initial clamp voltage” and it is measured at 1 mA of surge current. It determines the maximum system voltage where the suppressor can be used.
Another important specification is the “let through” voltage. This term describes the remainder of a spike that the suppressor passes and is usually given at a specific surge current to characterize the suppressor. For example, 330 V at 3,000 amps means that at a surge current of 3,000 amps, 330 V are passed on by the suppressor.
Q: Should surge protection be put on every device in a building?
A: No. Sometimes surge protectors cost more than the electronic device they need to protect. Only devices that are costly, connected to expensive equipment, or cause a lot of labor to repair should be protected.
Q: Are surge protectors 100% effective or is there still risk involved?
A: Surge protectors are like insurance; you get what you pay for. Inexpensive suppressors can be effective or useless, depending on their design. Properly designed and installed surge protectors are about 99% effective. However, a direct lightning strike can destroy even the best suppressors, so there is never a 100% guarantee.
