Well, how do you choose a surge protector?

An engineer may say, "Determine the level and quantity of surges you want to protect against, then buy a surge protector that is tested to handle the matching quantity and level of surges." That is all very well but how do we determine the level of surges and the number that can occur in a given period of time? In practical terms, this is almost impossible. There is equipment available that will measure and record powerline disturbances and this could give you an idea of the typical surges that are present in a particular building, but that one destructive surge that suddenly destroys thousands of dollars worth of equipment may occur this week or may not occur for a number of years. An isokeraunic chart can give an idea of the possible frequency of lightning activity in a given area but no one can say when a particular building will get hit. The only sure way of protecting equipment from that "killer" surge is to purchase a surge protector that is capable of handling surges as specified in IEEE/ANSI C62.41-1991 (6000V, 3000A).

The above discussion gets straight to the "bottom line," but there are other points worthy of discussion. Are there applications that might not require a Grade A, Class 1, Mode 1 product? Only the installer can make that determination or trade off, but there are some factors to consider here. Equipment that is not interconnected to equipment which is plugged into a different power outlet should not have a problem with the ground contamination caused by shunt mode protection. However, if this trade off were chosen the installer must remember the lifetime limitation of MOVs (for a shunt mode product) and determine a replacement schedule. Failure to take this step can leave equipment totally unprotected!

The actual type of equipment to be protected can also guide the decision making process. MOV-based shunt mode protection does not clamp as efficiently as Series Mode® protection and does not limit the extremely fast rise-times of transients. Computer modeling has shown that, due to the way in which they operate, MOV-based products do not protect certain types of power supplies, especially switching power supplies. The modeling shows the extreme nature of this problem to the extent that the power supply is protecting the MOV! Any equipment that contains a switching power supply should therefore not be plugged into a shunt mode surge protector. A computer application should not be plugged into a shunt mode surge protector for two reasons: because it contains a switching power supply, and because ground must not be contaminated in a networked system. (The datacomm ground is the same ground as the safety ground).

Remember -
Ask your supplier for the endurance rating before buying a surge protector!