Lightning and Surge Protection Systems in Bangladesh

Does my building need lightning protection?

IEC 62305-2 answers this with a risk assessment rather than a rule of thumb. It weighs the building's size and height, how isolated it is, local lightning frequency, construction, occupancy and what a strike would cost in lives, services and equipment. Bangladesh sees frequent thunderstorms, especially in the pre-monsoon months, so many buildings come out needing protection.

The assessment also sets the lightning protection level, from I to IV, which decides how closely air terminals and conductors are spaced. A garment factory with hundreds of workers and a roof covered in solar panels may need a higher level than a storage shed of the same size.

How is the roof protected?

IEC 62305-3 gives three methods for placing air terminals: the rolling sphere, the protection angle and the mesh. Large flat factory roofs usually suit a conductor mesh with short air rods at corners and edges, while rooftop plant, water tanks and solar arrays are checked with the rolling sphere so nothing sits outside the protected zone.

We design to these methods. Early streamer emission terminals, sold as covering a wide radius from a single rod, are not part of IEC 62305 or NFPA 780, so we do not size systems on those claims. Down conductors are spaced around the perimeter, each with a test joint so its earth can be measured on its own.

Why are surge protective devices part of the job?

A strike on or near the building induces surges in power, data and CCTV cables, often damaging inverters, PLCs, fire alarm panels and cameras even when the structure is unharmed. IEC 62305-4 deals with these effects. We fit Type 1 SPDs where the supply enters, Type 2 at distribution boards and finer protection at sensitive equipment, coordinated so each stage does its share.