- What is TVSS?
TVSS is an abbreviation for "transient voltage surge suppressor." A TVSS is a device that attenuates (reduces in magnitude) random, high energy, short duration electrical power anomalies caused by utilities, atmospheric phenomena, or inductive loads.
Such anomalies occur in the form of voltage and current spikes with a duration of less than half an ac cycle. These high energy power spikes can damage sensitive electronic equipment, such as computers, instrumentation, and process controllers.
- How do surge suppressors work?
Surge Suppressors are designed to divert high energy power away from a load by providing a lower impedance path to common point earth ground. Surge suppressors used most often for panelboard protection have metal oxide varistors (MOVs) connected in parallel.
- What types of components make up a surge suppressor?
The device most commonly used in an ac surge suppressor is an MOV comprised of solid-state zinc oxide with multiple junctions.
MOVs provide low impedance when conducting, and are packaged for specific voltages and current handling capacities.
Other devices (more typically found in dc applications) include single junction diodes and gas tubes that ionize at preset voltages.
- Where are surge suppressors installed?
AC surge suppressors are typically installed in these three areas:
I. at a utility service entrance for protection of an entire facility.
II. in distribution panelboards and switchboards for protection of sensitive downstream loads.
III. connected to a wall outlet for individual protection of a specific piece of equipment, such as a computer or solid-state controller.
- What is surge current capacity?
Surge current capacity, as defined by NEMA standards, is the maximum level of current a surge suppressor can withstand for a single transient event. This level is used to indicate the protection capacity of a particular surge suppressor design, and when specifying a suppressor for a given application. For example, in a high exposure application with very large transients present from lightning, a higher level surge current capacity would be required.
- What is clamping voltage?
Clamping voltage-also referred to as peak let through or suppressed voltage rating-is the amount of voltage a surge suppressor permits to pass through it to the attached load during a transient event. Clamping voltage is a performance measurement of a surge suppressor\'s ability to attenuate a transient. This performance value is confirmed by Underwriters Laboratories during tests conducted while evaluating a surge suppressor for listing.
- What features should be considered when selecting a surge suppressor?
Two important areas to consider during the selection of an surge suppressor are performance and safety, and include the following criteria:
Performance: 1) surge current capacity; and 2) clamping voltage.
Safety; 1) the individual suppression circuit should be fused to clear an inoperative MOV during an extreme transient event, and 2) provide overcurrent protection for the surge suppressor during a fault condition.
- What surge current capacity is required?
Surge current capacity is dependent on the application and the amount of required protection. The selection of the proper surge suppressor is not an exact science and cannot be scientifically calculated from a standard algorithm.
The following are frequently asked questions about surge suppression, and definitions of terminology used when specifying surge suppressors.