The silicone rubber housing is directly molded onto the metal oxide (MO) blocks and the surrounding cage made of FRP rods. This creates a reliable seal that prevents moisture ingress and partial discharges.

The MO resistors are not surrounded by a rigid mechanical coating, which is why no critical increases in pressure can occur in the surge arrester in the extremely rare event of an overload. The arc can escape directly through the soft silicone housing without damaging the mechanical structure. No internal parts are ejected in the process. The innovative Siemens cage design is very secure.

The silicone rubber is highly hydrophobic. This keeps any conductive moisture from forming on the surface, and dirt deposits are rendered harmless as a result of the hydrophobic transfer. Silicone is highly fire-retardant and self-extinguishing in the event of fire. These properties ensure the reliable, maintenance-free operation of 3EK surge arresters.

Siemens offers two types of products for use in distribution networks that differ in terms of mechanical strength:

• 3EK4 – for rated voltages up to 36 kV, high mechanical strength
• 3EK7 – for rated voltages up to 60 kV, very high mechanical strength

The proven type 3EK7 surge arrester is also available for indoor use. The 3EK7 surge arrester for indoor use is a cage design surge arrester that offers the same features as the version for outdoor use.

In the extremely rare event of an overload, arcing cannot result in a buildup of critical internal pressure, since the MO resistors are not enclosed in a sealed rigid mechanical shell. The arc can escape directly through the fiberglass wrap and the soft silicone housing without damaging the mechanical structure. No internal parts are ejected in the process.

High-temperature vulcanized (HTV) silicone rubber is highly hydrophobic. This keeps any conductive moisture from forming on the surface, and dirt deposits are rendered harmless as a result of the hydrophobic transfer. Silicone is highly fire-retardant and self-extinguishing in the event of fire. These properties ensure the reliable, maintenance-free operation of 3EK8 surge arresters.

3EK8 surge arresters can be delivered with the same accessories like 3EK7 surge arresters.

The APS is available for type 3EK4 and 3EK7 surge arresters. We recommend using surge arresters with APS in especially hot and dry regions with an increased risk of forest fires – like the western United States and South Australia.

The surge arresters can also be equipped with a visible failure message. A red display appears at the bottom end of the surge arrester in the event of a malfunction.

Siemens medium-voltage arresters for distribution networks with APS meet all of the requirements of the Cal Fire Power Line Fire Prevention Field Guide (2008), and have successfully passed all necessary tests. Siemens surge arresters with APS also have a much lower rate of sparks than surge arresters without APS.