Lightning has been the subject of research for decades. Extensive research has been conducted by the University of Queensland in Australia on the failure mode of surge protectors during multiple strokes. They have created a multi-pulse (6 stroke) generator that is capable of providing a time interval of between 20 to 130 ms per pulse. This is to simulate the effects of multi-stroke lightning events which may destroy a surge protector.
This multi-pulse generator uses a series of capacitors that are connected to the pulse forming network by a bar switch which is connected to a pendulum. As the pendulum swings through the charged capacitors, it discharges the capacitors into a pulse-forming network. The time interval between switch contacts is a function of the period of the pendulum. It has been found that fairly short time intervals between pulses will have a severe effect on the performance of surge protectors and also may cause nuisance fuse operations.
The result of multi-pulse generator testing on surge protectors has shown that the edge of the zinc oxide metalized area on any MOV is the most critical region when subjected to this kind of pulsing. It was also found that in some cases the temperature can rise to between 800° and 1000° C in isolated “hot spots” in the MOV volume, resulting in failures from punctures of the zinc oxide material. Also, plasma accumulates on the edge of the metalized area and causes additional breakdown regions. The Australian team concluded from their research that the actual rating of an MOV device can be as much as 100 to 150% of the nominal rating for a single pulse; and 60 to 75% of the rating for multiple pulses, if the device is not energized; but may be between 30 to 40% of the rating for multiple pulses if the device is energized.
For more details about lightning read APT’s engineer bulletin: Lightning: Physics and Effects (pdf)
UL96A Lightning Protection Master Label
Underwriters Laboratory (UL) is a global independent safety science company and has developed more than 1,000 Standards for Safety. The lightning protection certification, UL96A, is the standard for installation requirements for lightning protection systems. The 12th Edition of UL96A is the current version, it was released on May 23, 2007.
Previously, UL96A required surge protectors evaluated as secondary arrestors for lightning protection systems. But there were issues associated with different regulation and administration. With the recent industry changes secondary surge arrestors (i.e. lightning arrestors) have evolved into Type 1 SPDs. In order to be compliant with the surge protection requirements for UL96A, lightning protection installers must utilize a surge protector that is a Type 1 or Type 2 listed SPD having 20kA In ratings.
Below is a list of APT’s surge protector products that meet the requirements for UL96A Lightning Protection Master Label*
(* Note that some rare voltages ratings on the above list of products do not meet the 20kA In requirements. Reference the spec sheets for applicable voltages.)