The short answer
A lightning conductor does not attract or stop lightning. It gives a strike that was going to hit the building anyway a low-resistance metal path from the roof to the ground, so the current flows harmlessly into the earth instead of through brick, stone, timber and wiring.
On this page
A lightning strike carries a current of thousands of amps for a fraction of a second. When it hits a building with no protection, that current looks for the easiest way down. It might find it in a damp stone wall, a lead roof, a timber beam, a steel frame or the electrical wiring. Wherever the path is poor, the current heats things very fast, and that is how stone cracks, timber catches fire and electrics fail.
A lightning conductor, or more properly a lightning protection system, solves this by offering a better path. It is not a magnet for lightning and it does not “discharge” storms. It simply makes sure that when a strike lands, it lands on metal designed to carry it.
The three jobs a lightning conductor does
Every system, from a single rod on a church tower to a mesh on a hospital roof, does the same three things.
1. Catch the strike
The top of the system is the air termination: vertical rods, horizontal conductors along ridges and parapets, or a grid of tape across a flat roof. Its job is to be the thing the strike hits. Designers use a method called the rolling sphere, set out in BS EN 62305-3, to decide where it needs to go. They imagine a ball rolled over the building; anywhere it can touch needs metal. Our guide to BS EN 62305 explains the sphere sizes for each class.
2. Carry it down
Down conductors are the strips or rods of copper or aluminium you see running down the outside walls. They connect the air termination to the ground by the most direct route. Larger buildings have several, spread round the outside, so the current divides and no single conductor carries all of it. Splitting the current also reduces the chance of it jumping across to pipes, cables or people inside.
Each down conductor has a test clamp a couple of metres off the ground. It looks like a small metal plate bolted across the tape, and it lets a tester separate the conductor from its earth during the annual test.
3. Spread it into the ground
At the bottom, each down conductor joins an earth electrode: usually a copper-bonded steel rod driven several metres into the ground, sometimes a buried ring round the building. The electrode’s job is to hand the current to the soil quickly. How well it does that is measured as earth resistance, and BS EN 62305 recommends a figure of 10 ohms or less for the system as a whole, as Historic England’s guidance notes.
Why a conductor does not make a strike more likely
This is the most common worry, especially for churches and homes. The building’s height, shape and position are what make it a target. A tall tower on a hill is likely to be struck whether or not it has a conductor. The conductor only decides what happens next. A rod on the roof adds a few metres at most, which is not enough to change the odds for most buildings in any meaningful way.
What a conductor does not protect
A lightning conductor protects the structure and the people in it from a direct strike. It does not protect the electrics. When a strike hits the system, or hits the ground or a cable nearby, a voltage spike travels along power, phone and data lines into the building. That is the job of surge protection devices, fitted in the distribution boards. A complete design under BS EN 62305 includes both.
What can go wrong
Because a lightning conductor sits outside for decades, it wears.
| Problem | What causes it | How it shows up |
|---|---|---|
| Corroded joints | Rain, pollution, mixing metals | High continuity reading |
| Loose or missing fixings | Soft mortar, frost, wind | Tape hanging off the wall |
| Stolen tape | Copper’s scrap value | Missing sections, usually low down |
| High earth reading | Dry soil, corroded rod, ground works | Earth resistance above target |
| Parts cut or covered | Roofers, scaffolders, new plant | Gaps found on the visual check |
A system with a broken path can be worse than none, because it invites the strike onto a route that stops part way down. That is why systems are inspected and tested regularly, and why the Department for Education asks schools to do it at least once a year.
Old systems and new standards
Many older buildings, churches especially, have a single rod and down conductor fitted decades ago to the withdrawn British Standard BS 6651. They can still work, and they can be tested. But the current standard usually expects more down conductors and earths, so the test report may mark them as a conditional pass and suggest an upgrade. See repairs and upgrades for what that involves.
If you are responsible for a building and are not sure what is on the roof, or when it was last tested, the lightning protection homepage explains what to do next. When you want a specialist to look at it, use the form below.
Where our information comes from
- Historic England, Lightning Protection (HEAG182), April 2019
- Department for Education, Good estate management for schools: health and safety, updated July 2026
- BS EN 62305-3:2011, Protection against lightning: physical damage to structures and life hazard, BSI