Does a Metal Spike Attract Lightning or Repel It? Neither, Exactly

Lightning strikes where the electrical conditions favour it, and a building struck without protection conducts the current through whatever path it finds, which means through masonry, wiring, plumbing and occasionally people, with the heat generated by resistance causing fire and explosive damage. A protection system provides a deliberate path of much lower resistance, consisting of a metal terminal at the highest point, heavy conductors running down the structure and a connection into the ground. Current entering the terminal follows that path and dissipates into the earth without passing through the building. The device does not prevent a strike and does not meaningfully attract one from a distance, and it determines where the current goes once a strike occurs.

The terminal is the visible part and the least important:

• •One or more air terminals at the highest points of the structure
• •Down conductors of adequate cross section, ideally more than one path
• •A low resistance earth connection, which is where most systems fail
• •Bonding of metal parts nearby, to prevent current jumping across gaps
• •Surge protection on electrical and data cables entering the building
• •Regular inspection, since corrosion and damage accumulate invisibly

Benjamin Franklin proposed the device in the early 1750s, having argued that lightning was electrical and having demonstrated it by experiments drawing charge from storm clouds, and the protective application followed immediately from the understanding. It was among the first cases where investigation of a natural phenomenon produced a practical device that saved lives, which contemporaries noticed and celebrated. A dispute followed about whether the terminal should be pointed or blunted, which became entangled with politics during the American revolution, with the British king reportedly favouring blunt ends in opposition to Franklin's pointed ones. Modern testing has found the question genuinely unsettled, with some evidence favouring blunter terminals.

Personal safety in a storm depends on a few facts that are widely misunderstood. A closed vehicle is safe not because of its tyres, which is the usual explanation and is wrong, but because the metal body conducts current around the occupants and into the ground, which is why a convertible or a fibreglass boat offers nothing. A building with wiring and plumbing is safe for the same reason, provided nobody is touching those systems, which is why advice against using a bath or a corded telephone during a storm is sound. Open ground, isolated trees, water and high points are the dangerous places. The rule relating the delay between flash and thunder to distance gives roughly three seconds per kilometre, and a strike can occur well beyond the visible storm.

Protecting buildings from lightning raised an objection that is now easy to underestimate, namely that lightning was widely understood as an instrument of divine judgement and that defending against it was presumptuous. The objection was made seriously, including from pulpits, and it had a specific practical edge because church towers were the tallest structures in most communities and were struck constantly, with bell ringers killed in considerable numbers while ringing bells to disperse storms, a practice that continued despite the deaths. The argument was settled by the evidence rather than by debate, since protected churches stopped burning down and unprotected ones did not, and adoption spread within a few decades.

A protection system supplies a low resistance path from a high terminal to the ground, so current from a strike dissipates without passing through the structure, and it neither prevents nor meaningfully attracts strikes. The earth connection matters more than the visible spike. Franklin proposed it in the early 1750s as the first life-saving device produced by scientific investigation, and objections that it defied divine judgement were settled by churches ceasing to burn.