Lightning Protection for Antenna Masts

Antenna masts are often the highest point on a building, which makes them a natural target for lightning. A direct strike is rare, but nearby strikes induce surges on feeders that can destroy radios, repeaters and network equipment inside. Autumn and winter storms are a good prompt to check that protection on existing sites is still in place.

The standard to work to

In the UK, lightning protection is designed to the BS EN 62305 series, which covers risk assessment, protection of structures and protection of electrical and electronic systems. Antenna installations on a protected building should be integrated with the existing lightning protection system rather than treated separately. Where a site needs a new or modified system, involve a qualified lightning protection designer.

Bond the mast

The mast or antenna pole should be bonded to the building's lightning protection system, or to a dedicated earth, using a conductor of suitable size. Keep the earth path short and straight. Sharp bends increase impedance at the frequencies found in a lightning surge, encouraging the current to jump to other paths.

Earth the feeder

• At the top: bond the coax outer to the mast close to the antenna using an earthing kit.
• At the bottom of the mast: bond again before the cable turns towards the building.
• At the building entry: bond the feeder and fit a surge arrestor before the cable reaches equipment.

Choose the right surge arrestor

Gas discharge tube arrestors pass DC, which matters if the feeder powers an active GNSS antenna or a masthead amplifier. Quarter-wave stub arrestors give excellent protection with low loss but block DC and are band specific. Match the arrestor to the frequency range, power level and connector type of the system, and check its insertion loss on the datasheet.

A single-point earth

Bring all earths for the radio equipment, feeders and the power supply together at one point. Multiple separate earths at different potentials let surge current flow through equipment as it seeks the easiest path between them. This is one of the most common causes of damage on sites that appear to be protected.

Inspection

Include earthing in routine maintenance. Check that bonding straps are present, tight and free of corrosion, and that arrestors have not been removed during equipment changes. Add these checks to the visit list in our storm season checklist and our mast and rooftop installation guide.

Frequently asked questions

Do all antenna masts need lightning protection?

Not always, but every installation should be assessed. BS EN 62305 sets out a risk assessment that considers the structure, its location and what it contains.

Will a surge arrestor stop a direct strike?

No device guarantees protection from a direct strike. Arrestors and bonding reduce the energy reaching equipment and greatly lower the risk of damage from nearby strikes.

Can I use a quarter-wave arrestor with an active GNSS antenna?

No. Quarter-wave stubs block DC power to the antenna. Use a gas discharge tube arrestor rated to pass DC.

For stainless steel mounts that make bonding straightforward, see the MAST/WALL MOUNT UNIVERSAL and the wider mounting range. For advice on a specific site, contact sales@renair.co.uk.