Separation Distances for Equipment on Roof
In order to provide for an isolated air termination system, the separation distance between the air termination rods and conductors and the rooftop plant had to be calculated to ensure that no inductance or uncontrolled flashovers of lightning currents onto the rooftop electrical equipment occurred.

Due to the fact that there are numerous down conductors and current division paths within the air termination system, a detailed approach to the calculation of the separation distances was applied. In order to calculate the separation distance ‘s’ the formula below was used.

Structures that have interconnected concrete reinforced superstructures in such a way that the reinforcing steel is able to carry lightning currents can be used as down conductors. The separation distance of these down conductors can be ignored due to the enhanced current division and the constant potential from the roof to the earth termination system.

PV systems have been installed in Europe for the past 15 years. Over time, research has determined that there are various factors that cause damage and downtime to these PV systems. The single largest cause of damage to PV systems is without doubt caused by lightning and induced surges.

There are also much higher risks of fire due to the fact that a large portion of the Free Field PV System utilises d.c. currents which do not disconnect under fault conditions. The cost of repair as well as the economic loss caused by downtime must be considered. There are also various other factors such as the premature ageing of the PV components and the risk of not meeting the PV plant`s contractual requirements on the amount of power being generated not being achieved must also be considered. The risk of damage caused by lightning must be determined in accordance with the SANS / IEC 62305-part 2 standard (please see our Risk Assessment White Paper) whereby the results of the risk analysis must be considered at the design stage.