Basic protective measures and equipment 

In order to ensure the total protection of a physical structure from the effects of lightning strikes and surge voltages, various protective measures or equipment that are tailored to one another are required. A broad classification is shown below: 

• External lightning protection 

• Internal lightning protection 

• Grounding and equipotential bonding 

• Coordinated SPD system

Internal lightning protection 

The internal lightning protection system should prevent dangerous spark formation inside the system. Sparks can be caused by lightning induced surge voltages in the external lightning protection system or in other conductive parts of the physical structure. 

The internal lightning protection system consists of the equipotential bonding system and electrical insulation due to sufficient distances or suitable materials from the external lightning protection system. 

The lightning protection equipotential bonding is intended to prevent dangerous potential differences. For this purpose, the lightning protection system is primarily connected to metal installations, internal systems, as well as electrical and electronic systems within the system. This occurs by means of equipotential bonding lines, surge protective devices or isolating spark gaps.

Grounding and equipotential bonding 

The grounding system aims to distribute and discharge the captured lightning current to ground. For this process, the geometry of the grounding system is crucial for effectively deriving lightning current (Not the grounding resistance value). Effective equipotential bonding is also important. Equipotential bonding connects all electrically conductive parts with each other via cables. Active conductors are integrated into the equipotential bonding via surge protective devices.

Test waveshape of impulse current 

This is the current that is used as one test parameter for determining the measured limiting voltage for SPDs tested according to the Type 1 and Type 2 tests. Iimp and Imax are test parameters used in the operating duty test for Type1 and Type 2 tests respectively. Imax is associated with Type 2 tests and Iimp is associated with Type 1 tests. 

In general Iimp is associated with longer waveshapes than In, The 10/350 waveshape is one example of a waveshape which meets the requirements of Type 1, 8/20 waveshape meets Type 2 measurement of the residual voltage at various values of current using 8/20 wave.