Figure 1. Indoor Cables Require Surge Protection, Too

Figure 2. Electromagnetic Radiation Triggers a Lightning-induced Surge

The Necessity of Surge Protection
Ethernet devices are typically considered to be immune to lightning damage since LAN cables are generally used indoors. However, such indoor use only ensures safety inside structures that can be expected to offer adequate protection from electromagnetic radiation (see Figure 1).

One reference reports, “In the event that a medium-strength lightning strike of 30kA occurs at a location 1km away, wiring routed at a height of 10m above the ground will experience a lightning-induced surge of at least 10 kV.” Those numbers are for outdoor wiring, but the fact that lightning releases enormous electromagnetic energy means that electromag-netic radiation passing through the building’s walls will trigger a lightning-induced surge in indoor cabling if the building does not offer adequate protection (see Figure 2).

On the other hand, when lightning strikes a lightning rod, high current flows to the grounding electrode through the lightning conductor. The strong magnetic field caused by this event can also pass through building walls, inducing a high voltage in any LAN cables that have been laid parallel to the lightning conductor (see Figure 3).

Figure 3. Induction of High Voltage in LAN Cables

Figure 4. Electric Potential Differences Between Ground Connections Are Superimposed as Overvoltages

Even if no lightning-induced surge enters the LAN cable, potential differences between ground connections may become problematic. When Ethernet devices are used in a large structure such as a factory, different ground connections throughout the building will experience different electric potentials during thunderstorms. Because the Ethernet devices are connected with LAN cables, differences in ground potential will be applied to devices as an overvoltage.

The lightning-induced surges and overvoltages superimposed on these LAN cables can cause damage to connected Ethernet devices (see Figure 4).

Hubs serve as the centers of most network topographies. Failure to protect them from damage ensures that any lightning damage will extend to the entire network. M-System identified this risk and developed the SHSP series to prevent the possible dangers described above.

The SHSP’s surge protection functionality is limited to its LAN ports. Please install a power supply surge protector for the power cord jack to provide blanket protection for other electronic devices. A separate surge protector for contact output need only be installed when transmitting data to a distant location.