The four parts

Air termination — the network of conductors or rods that intercepts the strike.

Down conductors — the path from the air termination to earth, routed to avoid side flashes.

Earthing — the system that dissipates the current, designed for the soil at the site.

Bonding and surge protection — the measures that stop the potential rise from damaging equipment inside the building.

Risk assessment first

The size and type of system follows from a risk assessment: structure height and dimensions, location and exposure, the consequences of a strike, and the presence of adjacent structures. A system sized without that assessment is a guess.

ESE and conventional systems

Conventional systems use a mesh or catenary network and are defined by geometry. ESE (Early Streamer Emission) systems claim a larger protected radius per unit, which changes the air termination layout. Whichever approach is used, the down-conductor and earthing requirements are not optional extras — they carry the current.

What is commonly under-specified

Too few down conductors, so the current takes an unintended path

An earthing system designed without a soil resistivity measurement

No equipotential bonding of metal services

No surge protection on incoming power and signal lines