EMP and transient suppressed mains filters

EMP protected mains filters currently being produced as standard products, provide various degrees of protection. Unfortunately, the precise degree of protection afforded is rarely defined clearly, and for a given filter range by a specific manufacturer, it can generally be deduced by the cost of the complete product. It is quite likely therefore, that when a particular range of EMP protected filters is more expensive than another, the difference in cost is often the key to the degree of protection provided. The author describes some tests which were undertaken to try and answer some of these questions, and attempts to put into perspective the different forms of EMP or transient suppressed mains filters which are generally available