The Difference Between Lightning Protection And Surge Protection

Lightning and surge protection are two elements of an effective electrical protection system.

Lightning is known to be the most significant source of surges—bolts have been recorded to have a million to a billion volts and between 10,000 to 200,000 amps. However, lightning only makes up a portion of all transient events in a facility.

Because transients can originate from both external sources (like lightning) and internal sources, facilities ought to have both a lightning protection system and surge protection installed.

Lightning Protection System

A lightning protection system protects a structure from a direct lightning strike.

To do this, an air terminal (or system of air terminals) is placed in the most probable position to capture the direct strike, based on the structure’s architectural design and roof equipment. The rest of the system is designed to safely convey that electrical energy from the lighting strike to ground as efficiently and safely as possible.

To intercept the strike and conduct the high current energy of a lightning strike into the earth, system components include the:

Air terminal, which is used to intercept the lightning strike.

Down conductors, providing the most direct path possible to move the electrical energy towards the ground.

Grounding system, which provides a path for the current to dissipate into the ground and out of harm’s way.

Bonding, meant to reduce the possibility of voltage differences that are a safety risk.

Lightning protection standards ensure how to properly place air terminals, run cable, ground and bond in order to ensure maximum safety in this energy transfer and dissipation.

Surge Protective Device (SPD)

A surge protective device (SPD) is designed to protect electrical systems and equipment from surge and transient events by limiting transient voltages and diverting surge currents.

What causes transients and surges?

Lightning is the most spectacular form of an externally generated surge, however, it is estimated that 65% of all transients are generated internally within the facility by the switching of electrical loads such as:


Heating systems


Other Inductive loads

How does a SPD work?

There is at least one non-linear component of the SPD, which under different conditions, transitions between a high and low impedance state. At normal operating voltages, the SPDs are in a high impedance state and do not affect the system. When a transient voltage occurs on the circuit, the SPD moves into a state of conduction (or low impedance) and diverts the transient energy and current back to its source or ground. This limits or clamps the voltage amplitude to a safer level. After the transient is diverted, the SPD automatically resets back to its high impedance state.

What Sets the Two Systems Apart?

On a basic level, the lightning protection system protects the facility and structure from direct strikes, while SPDs protect electrical equipment and systems against surges or transients.

How the two operate, and the components involved, also vary. Lightning protection system components are always in place and ready to function, while SPDs monitor internal system voltages and spring into action if a transient voltage occurs on the circuit.


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