SURGE PROTECTOR COMPARISONS

Evaluating power line surge suppressors is a difficult and confusing task. The significant differences between the Series Mode and Shunt Mode approaches are reviewed here to help reduce the confusion.

There are essentially two types of power line surge suppressors:

a) Shunt Mode (some versions of Shunt Mode are called Hybrid).

b) Series Mode.

Shunt Mode Suppressors:

a) Are simple and inexpensive. The primary suppression elements are normally two Metal Oxide Varistors (MOVs). These are small components the size of a quarter, which cost about a quarter in quantity. Three MOVs are often used but the third one is not functional, it merely allows a marketing claim to be made.

b) Shunt Mode suppressors work by clamping surge voltage and diverting surge current.

c) Shunt Mode suppressors do not suppress surge current, rather they shunt or "divert" surge current to the neutral wire and/or the Safety Ground wire. "One unfortunate side effect of most (shunt) surge suppressors is that they act by diverting surges into the building ground system. Interconnected data communications equipment depend on the ground voltage being the same in all parts of a building or network. In taking power line surges and noise and injecting them into the building ground, surge suppressors can create intersystem ground noise and therefore interfere with or damage data communications equipment." [1] This current diversion problem of shunt mode suppressors results in diverting power line surges away from a robust power supply to sensitive peripherals and data lines. Therefore, shunt suppressors should not be used with interconnected equipment.

d) "Surge suppressors (shunt mode) can and do catch fire. ........serious property damage and injury can result from such suppressor fires" [2]

Why risk using a product type that has nationally recognized fire and safety hazards associated with its use?

e) "The performance life of any shunt type surge suppressor utilizing MOV's is finite." [1]

Is it a good investment to risk your valuable equipment by using a product which is acknowledged by the manufacturers to be sacrificial and which degrades with use?

f) Shunt suppressors can withstand only a few maximum rated surges in their lifetime. Since you will not know when a given shunt suppressor has been exposed to its limit of surges, you will not know when to replace it. It's a roll of the dice!

Series Mode Suppressors: (Zero Surge)

a) Are safe. They do not explode, overheat or catch on fire.

b) Are effective. They suppress surge current, surge voltage as well as surge duration and operate over a very wide voltage range so they can repeatedly withstand surge currents that would disable ordinary shunt suppressors, and are even effective during brown-outs and over-voltage conditions.

c) Are reliable. They are certified to suppress the maximum industry standard surge of 6,000 volts, 3,000 amperes a thousand (1,000) times.

d) Are NOT sacrificial. They do not deteriorate with repeated use.

e) Are recommended for use with interconnected equipment, since they do not divert large surges to the Safety Ground voltage reference wire.

References:

[1] From Technical Note # T3 (8/91) by APC (American Power Conversion), a manufacturer of Shunt Mode suppressors.

[2] From a technical paper dated September 1992, presented at a POWER QUALITY '92 conference, by a Shunt Mode suppressor industry spokesman.