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1. What does TVSS stand for?
TVSS stands for “Transient Voltage Surge Suppression.” TVSS devices are also called “SPDs” or “Surge Protective Devices.”

2. How does a TVSS device provide protection?
Power surge protection systems reduce or eliminate harmful transients, surges and electrical line noise, thus preventing damage to sensitive electrical equipment. Each year, millions of dollars worth of hardware will be spared by installing surge and lightning protection equipment.

The most common forms of line surge protection are attenuation and diversion devices. Attenuation devices filter the transient within a set frequency to protect the sensitive load. Diversion devices actually direct the transient away from the protected load using either a “switching” or “nonlinear resistance” method. THOR SYSTEMS, INC. uses a combination of attenuating and diverting devices. Nonlinear resistance devices (Thermally Protected Metal Oxide Varistors and Silicon Avalanche Diodes) are used to achieve transient response times in the nanosecond range or less. Attenuating devices (Filter Capacitors) are provided to attenuate high frequency impulses below the suppression levels of the diverting devices (sometimes called “Sinewave Tracking”).

3. What are transients?
Transients are short duration power anomalies caused by the sudden release of electrical energy. Transients are also called spikes or power surges.

4. How do transients originate?
Over 80% of voltage spikes and impulses are caused by equipment inside yours or neighboring facilities. The starting and stopping of electric motors such as those used in automated systems and manufacturing (i.e., machine tools, elevators, HVAC, etc.) can create a continuous stream of 250V to 3000V transients. DC drives, variable speed AC drives, and DC power supply switching are other sources of transients and electrical noise.

Transients may occur either in repeatable fashion or as random impulses. Repeatable transients, such as commutation voltage spikes, inductive load switching, etc., are more easily observed, defined and suppressed. Random transients are more elusive. They occur at unpredictable times, at remote locations and require installation of monitoring instruments to detect their occurrence. Frequently, random transient problems arise from the power source feeding the circuit. These transients create the most concern because it is difficult to define their amplitude, duration and energy content. Random transients are generally caused by switching parallel loads on the distribution system, although they also can be caused by lightning.

5. Are transients really a Power Quality issue and do only computer applications require protection?
Transient over-voltages are a major cause of malfunction or total failure of electronic circuitry and equipment. These transients occur whenever there are sudden changes in a power distribution system, whether resulting from lightning or utility-switching disturbances on incoming power lines. These changes can create transients so intense they literally destroy sensitive electronics. Energy changes within the system are responsible for more than 80% of surge suppression events. With such changes, voltage spikes are created by the energy stored in reactive components (inductance and capacitance). These voltage impulses can destroy semi-conductor devices, reduce the dielectric strength of insulation, damage electromechanical contacts and cause logic circuitry errors by stray signals imposed on logic reference levels.

6. What causes computer and control system interruptions?
The three most prevalent types of system failure are: Catastrophic Failure, usually caused by arcing components or destroyed printed circuit traces; System Degradation of the sensitive electronic components and chip sets, continuously weakening until the component fails (normally this damage is not visible); and System Disruption power quality disturbances which are responsible for most of the unexplained and more elusive system lock-ups, data errors, communication errors and slow system operation faults.

7. Do most surge suppressors use the same technology?
No. Metal Oxide Varistors (MOVs) are the most widely used surge suppression device. They provide a fast response time and have high surge current capabilities within a relatively small package. Silicon Avalanche Diodes (SADs) are the closest to the ideal surge suppression device with very tight clamping curves and very fast response time, but SADs have limited current handling capability. Filter capacitors provide EMI/RFI attenuation for high frequency noise. Most manufacturers use either one or two of these technologies, but THOR SYSTEMS, INC. uses all three to create a hybrid design.

THOR SYSTEMS has integrated Thermally Protected Metal Oxide Varistors (TpMOVs) into our products. These TpMOVs utilize a patented “Fail-Safe” design technology featuring thermal and dielectric (arc shield) protection. Silicon Avalanche Diodes (SADs) are the closest to the ideal surge suppression device with very tight clamping curves and very fast response times, but SADs have limited current handling capability. Filter Capacitors provide EMI/RFI attenuation for high frequency noise. Most manufacturers use either one or two of these technologies, but THOR SYSTEMS, INC. uses all three to create a Hybrid 3-Tier design.

8. How are “Surge Arresters” and “SPD devices” different?
Surge Arresters and SPDs are addressed differently by both the NEC and UL. Within the NEC, Surge Arrester requirements are explained in Article 280 and SPDs are described in Article 285. UL did use two different test standards to evaluate the lightning arrestors and SPDs. However, defined in layman’s terms, a Surge Arrester was used to protect from flash-over and a SPD was used to protect actual connected equipment.

9. What is the impact of UL1449 3rd Edition (effective date September 2009)?
UL1449 3rd Edition is the UL Standard used to evaluate SPDs. UL1449 3rd Edition calls out the safety and performance tests required to obtain the 1449 3rd Edition listing. The latest UL1449 Listing should always be required of any SPD specified.

10. What is the impact of the NEC Short Circuit Current rating?
Under Article 285, Section 6 of the NEC – Short Circuit Current Rating, “the SPD shall be marked with a short circuit current rating and shall not be installed at a point on the system where the available fault current is in excess of that rating.”

It is a requirement of the NEC that the available fault current at the installation does not exceed the available short circuit rating of the SPD. This coordination can be achieved in two ways:

  • The SPD has a short circuit rating that meets or exceeds the available fault current at the installation, or
  • Provide a current limiting device (typically circuit breaker or fuse) to limit the short-circuit current exposure of the SPD device to a level that is below its short-circuit current rating.

11. What are important factors to consider when selecting a SPD?
Susceptibility is often referred to when describing the ability of an installation to be affected by surge events. Susceptibility can encompass much more than geographic location and is generally categorized by Exposure Level, typically listed as “high, medium or low.” Listed below are the key areas of susceptibility, which are described in detail in the applications documentation available for download on this Web site.

  • Electrical System Size
  • Geographic Location
  • System Voltage
  • Distribution System Configuration
  • Available Short Circuit Current “AIC”
  • Equipment Location Categories
  • Service Entrance
  • Distribution
  • Branch Circuits

The SPD installation should always be as close as physically possible, as cabling impedance can add as much as 100V per foot to the voltage surge suppression level.

Equipment Criticality is a vital consideration. Although assessments from the consulting engineer and electrical contractor are helpful, only the end user can determine the true cost of damaged and/or non-functioning equipment. Based on the importance of the protected equipment, the perceived susceptibility of the power distribution system may increase. Critical equipment may require an evaluation at a higher susceptibility due to the requirement of little or no down time. In these locations, normal selections based on exposure levels and equipment location categories may be increased due to the equipment being protected. Some examples of this type of equipment are Data Processing, Medical, and Point of Use.

Although not always considered a part of the installation environment, Features and Benefits are an important aspect of the application process. Along with exposure levels and equipment location categories, features and benefits may drive the selection of a particular model or system. Features or benefits promoting serviceability, performance, inter-connectability and available system information may influence the requirement of a certain series or product selection.

The installation environment may dictate certain features, e.g., an installation in a high exposure environment with extremely critical equipment may require a disconnect switch as well as field replaceable surge suppressors. This provides the means to be back online quickly in the event of a surge suppressor fault. Advanced monitoring could be another required feature. By providing an advanced monitoring system along with the capability to interconnect to the installation’s existing network, a facilities manager can have instant access to the surge protector system status.

12. How does ground impedance affect the performance of a surge suppressor?
A faulty or high impedance grounding system can render a SPD system ineffective. Most grounding installations of critical equipment call for the grounding system impedance to be 5 ohms or less. The NEC calls for a grounding system of 25 ohms or less in Article 250.56.

13. How is ground impedance determined?
At the service entrance, the fall of potential method is typically used by establishing either a two-point, three-point or four-point reference. These test methods require the use of specialized ground impedance test equipment that uses injection and reference electrodes to determine the ground impedance. Within the facility, clamp-on ground impedance instruments can be used.

14. What is the impact of EMI/RFI transients?
Electrical noise is spread by AC/DC motor controls, electronic lighting ballasts, printers, photocopiers and computers. Over time, and in connection with low-voltage spikes, electrical noise can cause sensitive electronic components to fail for no apparent reason.

15. Why are THOR SYSTEMS’ products superior?
Effective transient voltage surge suppression requires that impulse energy be dissipated by the surge protectors at a voltage low enough to ensure survival of the protected circuit components. A practical solution to protect against disturbances such as electrical noise, spikes and voltage transients is to install a hybrid surge suppression system which addresses very fast, high energy transients and has integrated electrical noise filtration.

For the very reasons noted above, THOR SYSTEMS developed the StakTraks™ suppression system design comprising multiple, independent parallel surge paths, surge planes and buss works which are key elements in providing improved transient suppression performance. This improved performance is accomplished by offering a lower impedance path between the hybrid design suppression elements and their conduction paths to direct the transient away from the protected equipment.

THOR SYSTEMS’ products are designed, manufactured, and tested in compliance with the following codes and standards: American National Standards Institute and Institute of Electrical and Electronic Engineers (ANSI/IEEE C62.41, C62.41.2, C62.45, C62.62, and C62.72); National Electrical Manufacturers Association (NEMA); National Fire Protection Association (NFPA 70 NEC); Underwriters Laboratories (UL 1449 and UL 1283); Federal Information Processing Standards Publication 94 (FIPS94); MIL-STD 220A. THOR SYSTEMS’ products are UL listed and labeled under UL1449 Standard 3rd Edition for Surge Protective Devices (SPDs) and UL 1283 Standard 5th Edition for Electromagnetic Interference Filters.

16. What is the THOR Site Shield 3g Risk Assessment Guide?
THOR SYSTEMS has developed a “Site Shield 3g Risk Assessment Guide” which provides a coordinated protection scheme throughout the facility. Installation locations with higher exposure levels (normally service entrance applications and critical equipment) have higher surge current ratings, while installations within the distribution system typically have lower exposure levels and therefore lower surge current ratings. With the Site Shield 3g Risk Assessment Guide, an installation can include larger TSr Modular systems featuring replaceable modules at or near the service entrance and TSn Non-modular units on the distribution panels, sub-distribution and branch circuits.

Electrical power quality problems cost the United States industries over $100 billion annually
80% of voltage surges and transients are caused by changes in electrical demand, inside the user's facility