A good ground is important for surge protection devices (SPD) to work properly. AC power SPD’s are designed to divert surge current to ground by providing the least resistive path. Without surge protection on the AC power, the surge current will look for other paths to a good ground. In many cases this path is found through electric/electronic equipment. Once the dielectric strength of the components in electronic equipment has been surpassed large currents begin to flow through the sensitive electronics thus causing failure.
UPS systems play a very important part in an overall power protection plan. They are designed to provide good clean uninterruptible power to critical equipment. They provide no protection for the communication and control lines found in today’s network type environments. They also do not normally provide AC power protection to the many nodes connected within the network. The surge protection elements found within even a very large UPS is very small in comparison to stand-alone SPD’s. Normally around 25 to 40kA. In comparison, our smallest AC entrance protector is 70kA and our largest is 600kA.
There are not many areas of the world today that do not experience surge-related incidents. Lightning is only one of the many causes of transient surge related problems. Today’s modern electronic equipment is much smaller, much faster, and much more susceptible to transient related problems than was the last generation of equipment. The sheer number of control and communication devices interlinked together in today’s networks make their susceptibility many times greater. These are new problems that were not nearly as frequent with previous generations of control equipment.
Many areas of the world do not experience as much lightning related problems as others. As much as companies today depend on their control and network systems, the system availability has become paramount. For most companies, a single surge related incident in a ten-year period, which causes the loss of system availability, would more than pay for proper protection.
Data and control interfaces suffer many times more damage from surges than do power supplies. Power supplies normally have some type of filtering and operate at higher voltages than do control or communication interfaces. Low voltage control and communication interfaces normally interface directly into the equipment through a driver or receiver chip. This chip normally has both a logic ground reference as well as the communication reference. Any substantial difference between these two references will damage the chip.
Even though all data lines stay within the building, communication interfaces are still susceptible to damage. There are two reasons for this. 1. Induced voltages from a nearby lightning strike when control/communications lines run near electrical power wires, metal in the building structure, or near lightning rod ground leads. 2. Differences in AC power voltage references between two devices connected together by control/communication lines. When an event, such as a nearby lightning strike, migrates in on the AC power, individual equipment within the building can see large voltage reference differences. When these devices are connected together by low voltage control/communication lines, the control/communication lines try to equalize the difference, thus causing damage to the interface chips.
Full protection is one of the most inexpensive insurance policies you can buy. The cost of system inavailability is far more expensive than proper protection. One major surge event in a ten-year period far outweighs the cost of protection.
The protection the Phone Company provides is there mainly for personal safety to prevent lightning from migrating in on their wires and causing personal injury. It provides little protection for sensitive electronic communications equipment. It provides primary protection but does not eliminate the need for secondary protection at the equipment.
Metal housings are frequently used for TVSS because of the risk of failure causing fires or even explosions. UL1449 2nd Edition dictates that TVSS units MUST have safety features that prevent fires or explosion in the event of failure. All ASC products are independently tested by UL to ensure that they fail safely. In addition, the Thermo plastic box is NEMA 4X rated with gasket doors. This means that it is an Indoor/Outdoor unit. The housing is corrosion proof and UV stabilized. The clear door allows the status of the modules to be read clearly through the door, removing the necessity of lights in the door and the associated circuitry