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How to prevent power surges
March 2011, Electrical Power & Protection

The leading cause of serial device server failures.

Voltage spikes are brief events that rarely last more than a few microseconds, but all it takes is one snowball to set off an avalanche. In complex systems, even seemingly small events can have serious consequences. This is definitely true of industrial automation systems, in which many different devices need to work together in order to maintain normal operations.

Computers and communications equipment are essential components of many modern automation systems; however, they are also particularly susceptible to power surges from voltage and current spikes because they typically have low dielectric strength. In these systems, serial device servers are key communications gateways that connect the broader Ethernet network with specific serial devices. A power surge that damages this vital communications link will bring the entire process to a halt.

What causes power surges?

A voltage spike is a momentary extreme burst of electricity in an electrical circuit. This energy spike may be short-lived, but could still be strong enough to damage the electronics. There are many potential sources of power surges, two of the most common are lightning and switching surges.


Lightning creates substantial electric discharge at the location it strikes. When it strikes a building directly, it can clearly endanger its electrical system, but there are also other ways for lightning strikes to cause a power surge. For example, when lightning strikes a power transmission line, the effects can cause equally dangerous voltage spikes miles away.

Lightning is an ever-present threat to sensitive electronic systems. Of course, lightning strikes are more common in some regions than others. Nevertheless, even in locations with infrequent strikes, lightning poses a significant risk and its consequences must not be underestimated.

Switching surges

There are many malfunctions in electrical equipment that can lead to power surges. Tripped circuit breakers, short circuits, or even power transitions can all create switching surges. These electrical irregularities may be man-made but can cause just as much damage as lightning. A large power substation that regularly cycles on and off generates enough switching surges to threaten sensitive electronic devices.

Gaps in existing power surge protection

Industrial automation operators generally understand that power surges pose a serious threat to their systems and take steps to reduce this threat. Not only do power surges damage and destroy equipment, they cause costly interruptions. In the case of serial-to-­Ethernet communications, irreplaceable historical data could be lost if the serial or Ethernet ports suffer a power surge.

For a serial device server, there are three major points of weakness that could be damaged by a power surge: the serial line, the Ethernet line, and the power line. Many serial device servers offer surge protection on the Ethernet and power lines to protect against this threat. However, most serial device servers leave the serial line unprotected. As a consequence, the serial line is often the vulnerable chink in a serial device server’s surge protection armour.

Interested readers can view the full Moxa white paper and learn more about Moxa’s full spectrum of surge protection solutions at

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