Transients generated inside a building or office are very common. They come from three sources -- electrostatic discharge (ESD), device switching, and arcing.

ESD, in one sense, is like a very small lightning strike. Static electricity builds up between two dissimilar materials. The attraction force that results between them is what we colloquially call static cling. If the electric field between these materials becomes large enough, an arc occurs, discharging the buildup.

Humans usually don't feel a static "zap" unless the voltage is above about 1500 volts. But voltage levels as low as 500 volts can disrupt and even damage electronic components.

Reactive loads turning on and off generate spikes whether these loads are heavy motors or copy machines. The term "reactive load" is somewhat generic. Basically, any piece of equipment can cause impulses. The compressor motor in a soda vending machine is one example. Computers and their peripherals is another. HVAC and refrigeration equipment can also be culprits.

Another source of transients is from arcing. Arcing occurs when there are poor or degraded connections in the wiring system. A loose phase conductor in a panel is a good example. As the loose wire moves a little, arcing is seen which creates spikes.

Arcing is almost always associated with other disturbances also. Momentary interruptions, higher voltage distortion, and sags are likely companions to arcing.

One of the main concerns regarding transient protection is not so much how to protect the input power side of the PC, but how to protect the data cables and I/O ports.

There is a problem from transients known as "back door hits." This refers to the issue when a transient enters a computer through the I/O ports rather than from the power lines. This occurs whenever a distributed system such as a computer with several monitors in different parts of the business or a LAN has components which are not protected, yet are connected to each other via the data cables.

A spike hits one component (say an external monitor) and some of the energy gets on the data lines. This energy then travels to another system component (say the main computer) and enters through the I/O port. Data disruption and lock-ups may occur, even though the main computer's power is protected.

Most of the time it is difficult to determine where transients are coming from. Yet wherever they originate, most of the solutions are similar. TVSS systems and power conditioners, when properly specified and installed, can reduce transients to non-damaging levels.

These devices are usually installed at the plug level. In other words, they plug into a standard outlet, and the sensitive device plugs into it.

Data line protectors may also be used to prevent back-door hits. These are small devices that connect directly to the output port, and the data cable connects to it.

By troubleshooting and diagnosing the transient activity, it is possible that the source of the spike can be located. If this is done, then three more options exist.

First, if the offending device is failing or there is a bad connection somewhere, get it fixed. Eliminate the source rather than attempt to protect everything else.

Second, try stopping the transient at the source if it cannot be eliminated. Place a power conditioner on the vending machine, for example. This will prevent the normal spike of the compressor motor from traveling to other loads.

Third, relocate the offending device or the sensitive device. The normal wiring system is a great transient reducer. Rather than plug the computer into an outlet that is on the same circuit as the transient generator, find another. It is far cheaper to address these problems at the source, or side-step them altogether, than to invest the time and money into device-based solutions.

Links to Related Topics

Wiring and Grounding
Voltage Sags