Selecting Transient Voltage Surge Suppressors
There are three main categories of Transient Voltage Surge Suppressors (TVSS); Main Disconnect Panel or Meter Base, frequently referred to as "whole house" (type C), Sub-Panel or Distribution Panel (type B), and point-of-use plug-in (type A). These three types may be used individually, or together, depending upon the requirements of a particular situation.
Transients may be generated outside of the home or business by lightning, other utility customers, car accidents, animals, and even normal utility switching operations. Inside the home or business, transients are generated by motors starting and stopping, florescent lighting, copiers, vending machines, welders, and many other sources. The best protection for sensitive electronic equipment is to use a layered approach. Whole house protection to mitigate the larger transients coming from outside the home or business, and point-of-use surge protection for equipment sensitive to transients generated within the building.
The following guidelines were designed to help you become an informed consumer, and to help you identify the proper equipment for your particular situation. If you have questions, or need additional assistance, please contact us.
- Underwriters Laboratories Standard #1449 - Verify that the Surge Suppressor is Underwriter Laboratory (UL) listed for compliance with their standard #1449. This testing verifies compliance by including on the product; the product's identity (Transient Voltage Surge Suppressor), the UL symbol, and the word "listed," all in close proximity. Caution: UL listed means the device was tested and passed the testing. The words "UL Tested" mean only that the device was tested. The results of that test remain unknown. Additionally, UL Standard # 1449 only provides assurance that the device meets certain safety standards, it is not a guarantee of performance.
- Clamping Voltage - Various protection levels are covered under the UL 1449 listing, including 330, 400, 500, 600, 800 and six other levels up to 4,000 volts (only 330, 400, 500, and 600 apply to plug-in models). A lower clamping voltage is generally better. Where multi-stage surge suppression is being used, the TVSS at the service entrance usually has a higher clamping voltage (which in turn allows for a higher total energy dissipation) than the installed point-of-use devices. Have your electrician verify that the devices are "coordinated" so that they work together to provide the proper protection.
- Total Energy Dissipation - This is the maximum surge energy that the unit can handle without being damaged. A larger number is better.
- Maximum Continuous Operating Voltage (MCOV) - This is the maximum designated
rms (root-mean-square) value of 60 Hz voltage that may be applied between the terminals
of the arrester. Choose an MCOV rating capable of sustaining 125 percent of the nominal
rms voltage without degradation.
- For example, if the nominal RMS voltage of the system
is 120 volts, select a device with a MCOV of at least 150 volts.
120 volts x 1.25 = 150 volts
- For example, if the nominal RMS voltage of the system
is 120 volts, select a device with a MCOV of at least 150 volts.
- Common Mode and Normal Mode Disturbances - The TVSS devices should be designed to protect against transients in four electrical modes including common mode (line-to-ground V3, neutral-to-ground V2) and normal mode (line-to-neutral V1, line-to-line*) disturbances.
- Sine Wave Tracking - This technology tracks the AC sine wave, permitting instant response to minor spikes and transients that will pass through conventional protection. These devices cost significantly more than conventional TVSS technologies.
- Fault Clearing Devices - The surge suppressor should be fused or have a melting link to isolate the device should it fail. There are two designs for these fault clearing devices. One design interrupts power to the load being served, while the other design isolates the TVSS without interrupting power to the load. The preferred method of fault clearing must be determined for each particular application.
- *240 Volt or 3-phase only, not represented by graphic.
- Indicator Lights - Choose TVSS devices with indicator lights which show that the device is functioning properly. Some suppressors have audible alarms or provide auxiliary contacts for remote monitoring and supervisory control.
- Earth Grounding - In order for these devices to function properly, a low impedance earth ground is required. VERIFY THAT THE EARTH GROUNDING CONDUCTOR DOES NOT EXIT THE BUILDING THROUGH A METAL CONDUIT, UNLESS THAT GROUNDING CONDUCTOR IS ELECTRICALLY BONDED TO BOTH ENDS OF THAT CONDUIT!
- Locating Whole House TVSS Devices - In most situations within the Wisconsin Public Service territory, the earth-neutral bond is within the customers main disconnect panel. Therefore, to keep lead lengths short (important for optimal performance of TVSS devices), it is recommended that the whole house TVSS devices be located on this panel rather than at the electrical meter. This location also permits installing the device with a dedicated breaker which will facilitate future maintenance and replacement.
- Other Important Considerations - Telephone and other communications cables, TV antennas, and satellite dishes may be a path for destructive surges during lightning storms. For equipment with power and data ports, such as FAX machines, answering machines or cable TVS, use protective devices which provide protection for both the power and data ports. These systems should always be bonded (connected) to the electrical neutral. This is a code requirement which provides for personal safety and also helps prevent equipment damage.