Opera magazine

An impressive construction project, newly under way, protects the Cathedral and Bell Tower from the very serious risk of lightning strikes. Installed in 1859, the first lightning rod was made of copper strips, descending from the two metal crosses at the tops of the facade and the grand dome. The new project creates defences proportionate to the dimensions of this monumental building, making it the largest ever installed. The ancients observed how lightning hits in high places, but not knowing the reasons, saw something supernatural in the repeated strikes of firebolts against Verrocchio’s Golden Ball. Later there came the realisation that the sphere, and the flagpole at the very top of the dome, were true electrical collectors. It is for this very reason that the cross of Verrocchio’s Ball has for some time been equipped with receptors, and the two summital elements are now being re-equipped, for precisely this role. The new “Lightning Protection System” is designed to gather direct strikes and conduct the impacting electrical currents to the ground, for harmless discharge. The metal elements of the system are specifically designed, negating the risks of discharge during passage of the electrical currents. How will the lightning rod be made? The overall system if composed of several subsystems: the network of receptors, the elements designed to receive the lightning; the “down conductors", the components that conduct the current to ground, and finally the earth electrodes, responsible for discharging the energy to ground. The receptors, made of braided aluminium, are arranged along the rooftops, ridges, and all the projecting parts, creating an overall quadrangular mesh. The down conductors, also made of braided cable, conduct the current to ground along the most direct path possible, while remaining hidden. At the bottom of each vertical architectural element, these connect with the all-important earth electrodes, composing the dispersion part of the system. Underground copper cables join the electrodes in two circuits: one around the Cathedral and the other around the Bell Tower. The junction of the circuits creates one overall grounding system that ensures the protection our monuments, as well as all the people present. The down conductors follow hidden paths and the aluminium components will soon oxidise, blending with the marble of the monuments, creating an overall suit of “camouflage” armour. This very challenging construction project will last two years, but with little impact on the life of the square or the viewing of the monuments themselves. Wherever possible, the existing scaffolding will be used, and any aerial platforms will be present only for the time necessary. The trench for the dispersion circuit will be prepared one section at a time, running mostly in the spaces between nineteenth-century balustrade and the walls. This part of the work will also be the opportunity for preparation of a detailed record of the historic paving. In the centuries before the installation of the first lightning rod, in 1859, the cathedral dome suffered repeated dramatic strikes. Learn more about this story here. Anonimo fiorentino: Il fulmine colpisce la lanterna. Oxford, Ashmolean Museum, n. cat. 770.

Opera magazine

lighting

The new lightning rod of the Florence Cathedral