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What is a transient? An electrical transient is a temporary excess of voltage and/or current in an electrical circuit which has been disturbed. Transients are short duration events, typically lasting from a few thousandths of a second (milliseconds) to billionths of a second (nanoseconds), and they are found on all types of electrical, data, and communications circuits. What causes electrical transients? The simple act of turning on (or off) a light, motor, copy machine or any other electrical device can disturb the electrical circuit and create transients. In general, the larger the load current the greater the disturbance when the load is switched off or on. The switching of high ampacity loads such as electric welders and electric motors are known to create transients. Studies have shown that a majority of transients (roughly 80%) are generated inside a given facility. Cloud-to-cloud lightning discharges or nearby lightning strikes are capable of creating electric field intensities in the hundreds to thousands of volts per meter. A two meter length of wire (i.e. a power or signal conductor) exposed to an electric field intensity of 300 volts per meter can develop an induced transient voltage of 600 volts (2 meters X 300 volts/meter = 600 volts). If this 600 volt transient appears across an unprotected power, telephone, data, or coaxial line the result can be system destruction. A driver knocking down a utility power pole or a curious squirrel exploring a utility power transformer can be responsible for creating power interruptions and significant transient disturbances. Tree branches and even wet kite strings touching power lines have disrupted energy flow and caused power line transients. Noisy electrical neighbors sharing your electrical distribution system, such as welding shops, can also be a major source of transients. Should I cover the main or the branch panel? Should I cover both? Cover both and consider that an absolute minimum of two levels of protection is always required. The main panel or service entrance suppressor provides the first line of defense against large externally generated transients stepping them down to safe levels. These externally generated transients include those caused by lightning, downed power lines and similar distribution problems, as well as noisy electrical neighbors. The main panel unit also calms the internally generated transients which reach it from loads directly connected to it and from connected sub or branch panels. The main panel suppressor prevents the redistribution of these internally generated transients. Branch panel units handle the surge remnants which may remain after a massive hit at the main panel has been stepped down. Additionally, branch panel suppressor units prevent transient cross contamination between the various circuits and their connected loads. Point-of-use and individual equipment protection (always consider AC and signal protection) isolates the protected system from transient activity on the same circuit. What is let-through voltage? Transient suppression voltage or let-through voltage is defined in UL 1449 as "The maximum peak voltage occurring within 100 microseconds after the application of the test wave." What we are really talking about is the maximum amplitude or height of the voltage after the TVSS has done its job. Why are UL ratings important? The most important reason to look for the UL 1449 Second Edition Standard for Safety Transient Voltage Surge Suppressors listing is to ensure that the products are listed as complying with this safety standard. The UL 1449 Second Edition suppressed voltage ratings (let-through voltages) are determined as a part of the safety testing of the suppressor of UL 1449. This is the only data some manufacturers have because they do not have a UL 1449 certified laboratory or the staff, equipment, experience and certification required to test and certify their products with the various ANSI/IEEE C62.41-1991 test wave forms. Some manufacturers report let-through voltages that may represent measurements at the protection module, at the lugs, or some other measurement point which may give rise to artificially low values, which can not be achieved in an actual installation. The tip-off for artificially low numbers is when a table of let-through voltage is not provided with the test conditions and lead lengths involved. Energy Control Systems publishes let-through voltages on an as installed lead length basis in order to simulate an actual installation. The only way to get a true apples to apples comparison is to do the testing to simulate an actual installation. What safety listings do you carry? The safety listings for the various members of the Surge Suppression Incorporated® family vary by product design and intended application as required by the marketplace. The current safety listings are provided on the product data sheets. Some units are UL recognized components and are designed to be included in other original equipment manufacturers' equipment. How do you protect large motors? We protect a large motor just like any other electrical device or system. First, we conduct a survey to determine the electrical system flow and distribution characteristics (e.g., voltage, current, number of phases, number of conductors, Wye or delta, etc.). Second, we determine the points of entry or points creation of transients, such as lightning, and/or large inductive or capacitive devices. Next, we provide an cascade protection solution from the service entrance down to the individual equipment level as required. Generally, we will protect large motors with appropriately rated peak surge current capacity units - dependant upon their sensitivity and location in the electrical network.
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