•  A number of discrete electronic devices may be used as a suppression device or used in hybrid TVSS units.

•  Each type of device has strengths and weaknesses. Hybrid devices take advantage of the strengths of each and minimize the weakness.

•  Metal oxide varistors (MOV's) and gas discharge tubes (GDT's) are able to withstand severe transients. Silicon avalanche devices (SAD's) are unable to withstand severe transients but clamp at very predictable levels, experience no wear out and fail safe (short).

•  MOV's are offered in a wide variety of AC and DC operating ranges from a few volts to hundreds of volts. GDT's are offered in wider increments starting at 75 volts and going to several thousand volts. SAD's are offered in very fine increments from 5 volts to around 400 volts. All three devices may be stacked in series to provide alternate total voltages.

•  Resistors or inductors are often used in TVSS units to force the bulk of the transient into the primary device and protect the second or third stage. Multi-stage suppressors provide for high-energy absorption, low predictable clamping and often electrical filtering as well.

•  AC main and branch power TVSS devices are normally a shunt type because of the load currents involved. MOV's and GDT's are normally used in these locations. Some vendors will use a massive number of SAD type devices in these locations. Data/signal and Telco applications will generally be hybrid multi-stage TVSS units.

•  After one considers the threat, evaluates the risk and decides to procure a TVSS device, a reputable manufacturer or representative knowledgeable in the field should be consulted. TVSS suppliers who are competent in this industry will provide excellent advice regarding adequate design and model selection.

•  Great care should be given in the selection of the TVSS supplier and TVSS model. One should carefully examine specifications in performance since performance claims sometimes are worded to sound good but actual performance to accepted standards is often not referenced or is exaggerated.