All structures require some degree of maintenance ranging from roof fabric refurbishment to the addition of new roof mounted plant and equipment. In such circumstances the existing lightning protection system will be affected and will require modification.
General Wear And Tear
Even if no changes have been made to the structure, by the very nature of the system, it will be constantly exposed to the elements. Electrolytic action between the lightning conductor components is inevitable and should be checked for corrosion.
The requisite resistance to earth required of each electrode in the system, and the system as a whole, is clearly defined in BS 6651:1999 and the new European standard BS EN 62305:2006. Once installed the electrode resistances are affected by changing ground conditions and should be checked at 11 monthly intervals. 11 monthly intervals are recommended as the resistance to earth may also vary due to seasonal variations. Over a period of years, a picture can be built of how the seasons affect the earth resistances.
Earth resistances also have a tendency to increase year on year and it is therefore essential that the resistances to earth of each electrode be measured regularly and action taken to reduce any resistances which have risen above the recommendation criteria.
These criteria are specific to each system, dependent on the number of earth terminations installed.
It is also strongly recommended that if there is evidence or even a suspicion that a structure has experienced a direct lightning strike the system should be tested and thoroughly examined for any compromise in the systems integrity.