To protect equipment from overvoltage, vacuum switchgears usually include surge arresters. Arcing horns and lightning arresters are necessary because lightning strikes to the mast are common. ZnO discs, acting as a varistor, are the active material in most surge arresters. Both systems require flame or detonation flame arresters to maximize safety. Pole-mounted transformers often include accessories such as surge arresters or protective fuse links. Lightning arresters can form part of large electrical transformers and can fragment during transformer ruptures. Accessories such as instrument transformers, surge arresters, and capacitors are also made in compatible housings. Detonation flame arresters made by most manufacturers employ layers of metal ribbons with crimped corrugations. Lightning arresters are used to protect electric fences. The earliest electrical application of SiC was in lightning arresters in electric power systems. The LCC's electronics are fully shielded from Electromagnetic Pulse damage with carbon block surge arresters. The pad may also be protected by lightning arresters. Flame arresters are passive devices with no moving parts. It is also used in the construction of high-voltage lightning arresters. The earliest platforms for spark arresters in the United States were steam locomotives.