Lightning conductor tape: copper or aluminium?

The flat metal strip running down the side of a church tower or school hall is lightning conductor tape. It is the most visible part of a lightning protection system and the part most likely to be damaged, stolen or questioned by a conservation officer. The choice of metal affects how long the system lasts, how it looks and how often you will be replacing it.

The two main options

Historic England’s guidance puts it simply: aluminium is cheaper, lighter and easier to handle, but more likely to corrode, while copper is less likely to deteriorate and so has a longer life.

Where each one goes

Copper

Copper is the default for anything in or near the ground, including the tape running from the test clamp into the earth pit. It is also preferred in coastal and industrial areas where salt or pollution attack aluminium. Bare copper weathers over a few years to a brown and then green patina. It is available with a PVC covering in colours chosen to blend with stone or brick.

Aluminium

Aluminium is common for roof conductors and the upper parts of down conductors on large buildings, where its lower weight and cost matter. It should not be buried, laid directly on limestone or fresh mortar, or fixed where water runs off copper onto it, because those conditions speed up corrosion.

Joining the two

Where copper and aluminium meet, the joint needs a bimetallic connector designed for the purpose. A plain bolted joint between the two metals will corrode quickly, and a corroded joint is one of the most common causes of a failed continuity test.

Sizes and fixings

Tape for down conductors is commonly 25 mm × 3 mm in copper or aluminium, with round solid conductor used as an alternative on some systems. The BS EN 62305 series sets minimum cross-sectional areas for each material; a specialist will size the tape to the standard and the class of system.

Tape is fixed to the wall with clips, usually at about one metre intervals on vertical runs. On listed buildings fixings should go into mortar joints rather than stone, and routes should follow existing lines such as quoins, downpipes and buttresses so the conductor is less visible.

Theft

Copper’s scrap value makes it a target, especially at low level where it can be reached from the ground. Diocesan guidance asks parishes to check conductors regularly and repair damage quickly. Common responses:

• Guards over the lowest two or three metres, in steel or a tough plastic. Historic England asks that they are not visually intrusive.
• A different metal low down, where the design allows, with a proper bimetallic joint.
• Anti-theft fixings that need a special tool to remove.
• Marking the metal so it can be traced, and checking it after each storm.

Always tell your insurer and the police about a theft, and get a specialist to make safe any loose metal before it falls. A system with a gap in it can be worse than no system at all. See lightning protection repairs for what the repair involves.

How long does tape last?

There is no fixed lifespan, because so much depends on the air, the fixings and how well joints were made. Copper in clean inland air can last for many decades; the old copper systems still found on Victorian churches show what is possible. Aluminium in a coastal or industrial setting may need attention much sooner. What usually fails first is not the tape itself but the joints, clips and the transitions between metals, which is why the annual continuity test matters more than the age of the tape.

Signs it needs replacing

• Tape that has thinned, split or pitted along its length.
• White powdery corrosion on aluminium, or heavy green crust at copper joints.
• Clips that have rusted through or pulled out of the wall.
• Sections that have been bent or kinked by ladders, gutters or roof work.
• A continuity reading that has crept up year on year.

What to ask a contractor

• Which metal they propose for each part of the system, and why.
• How copper and aluminium will be joined, if both are used.
• What finish or covering they suggest for a listed or prominent building.
• What they recommend at low level to deter theft.
• The clip spacing and fixing method.

If your church or listed building needs work, our page on lightning protection for churches and historic buildings covers consent and intervals. Other buildings are covered on the lightning protection contractors homepage; to have a specialist look at your tape and fixings, fill in the form below.