Accessories for SPDs

In each mode, current flows through the surge protective components. What may not be understood, however, is that a different type of current can exist in each mode. Under normal power situations when ‘clean power’ is supplied within an electrical distribution system, the surge protective components performs minimal function. In the awaiting mode, the surge protective components is waiting for an overvoltage to occur and is consuming little or no ac power; primarily that used by the monitoring circuits. Upon sensing a transient overvoltage event, the surge protective components changes into the Diverting Mode. The purpose of an surge protective components is to divert the damaging impulse current away from critical loads, while simultaneously reducing its resulting voltage magnitude to a low, harmless level.

The magnitude of the surge current is dependent on its source. Lightning strikes, for example, that can in rare occurrences contain current magnitudes exceeding several hundred thousand amps. Within a facility, though, internally generated transient events will produce lower current magnitudes (less than a few thousand or hundred amps). Since most surge protective componentss are designed to handle large surge currents, one performance benchmark is the product’ s tested Nominal Discharge Current Rating (In). Often confused with fault current, but unrelated, this large current magnitude is an indication of the product’ s tested repeated withstand capacity.

The nominal discharge current rating exercises an surge protective components’ s ability to be subjected to repetitive current surges (15 total surges) of a selected value without damage, degradation or a change in measured limiting voltage performance of an surge protective components. The Nominal Discharge Current test includes the entire surge protective components including all surge protective components and internal or external surge protective components disconnectors. During the test, no component or disconnector is permitted to fail, open the circuit, be damaged or degrade. In order to achieve a particular rating, the measured limiting voltage performance level of the surge protective components must be maintained between the pre-test and post-test comparison. The purpose of these tests is to demonstrate the capability and performance of an surge protective components in response to surges that in some cases are severe but might be expected at the service equipment, within a facility or at the installation location.

A good quality plug-in SPD block is your best defense against AC voltage surges and spikes that can ruin your valuable equipment in a flash or build up damage over time. An electrical surge, or power surge, is an intense, short-duration voltage increase that travels through electrical wiring or other cables that transmit power or data. Most homes and offices in North America have electrical wiring with a standard voltage of 120 volts. Essentially, voltage is a measure of electrical pressure. In the same way that higher pressure on one end of a hose pushes water to an area of lower pressure and makes it flow out of the hose, greater electrical potential energy on one end of the wire moves electric current to the other end where the pressure is lower. When there's too much pressure in other words, when voltage significantly exceeds 120 volts it can damage electronic equipment. If an increase in voltage lasts three nanoseconds (billionths of a second) or more, it is called a power surge or transient voltage. If the increase lasts less than three nanoseconds, it is called a spike.

Common causes of surges and spikes include restoration of power after an outage, downed power lines, electrical grid malfunctions or accidents, on/off cycling of large appliances, wiring faults, tripped circuit breakers and lightning strikes. Very large surges, which are caused primarily by lightning and temporary interruptions resulting from storm damage, occur infrequently. They may happen a few times a year or several times a month, depending on the area. However, normal equipment operation may cause surges over 1,000 volts multiple times per day. The additional voltage in both surges and spikes generates extra heat that can seriously damage or completely destroy the circuit boards and other critical components in electronic equipment. The damage may occur all at once if the surge or spike is large enough, or equipment may be harmed incrementally over time by smaller, repeated power surges and spikes.