Surge Protection Devices (SPDs) are used to limit transient overvoltages and divert surge currents. They are primarily used in low-voltage power distribution and information systems for protection against lightning overvoltages, operational overvoltages, lightning electromagnetic pulses, and electromagnetic interference pulses. If protection against these overvoltages is required on the high-voltage side, lightning arresters are used.

When the surge current passing through the SPD exceeds its maximum capacity (Imax), the SPD can fail due to a breakdown, resulting in a short circuit fault in the circuit. To disconnect this short circuit fault, a circuit breaker or fuse needs to be installed. Each lightning strike causes aging of the SPD. For example, if the current is present for a long time, the SPD may overheat and age faster. At this point, the thermal protection system of the circuit breaker or fuse should act to disconnect the SPD before it reaches its maximum heat tolerance.


Requirements for SPDs on fuses and circuit breakers

When applying 20 standard 8/20 microsecond and 1.2/50 microsecond test pulses at the rated current, the circuit breaker or fuse should not trip. The circuit breaker orfuse should act when the SPD is short-circuited due to a breakdown. If the SPD is a switch-type module and fails by opening, it may not need to be equipped with a miniature circuit breaker and fuse for protection.

Both fuses and circuit breakers can be used as upstream protection for SPDs. Fuses feature long-delay and instantaneous current protection functions with inverse time characteristics, which are used for overload and short circuit protection. However, after a fault causes the fuse to blow, the fuse body must be replaced. Circuit breakers, on the other hand, offer instantaneous current protection and overload thermal protection. After a fault causes the circuit breaker to trip, it can be manually reset without replacing any components.



The choice of SPD depends on the incoming line: for a three-phase 280V five-wire system or a three-phase 380V four-wire system, a 440V SPD should be used. For a single-phase 220V two-wire system or a single-phase 220V three-wire system, a 220V SPD should be used. Also, note the protection level of the SPD: a 2nd level SPD should be used for a 280V three-phase input at a residential building, and a 3rd level SPD should be used for a single-phase 220V input.

In a TN-C-S system, after the PEN line enters the main distribution box of the building, it is divided into separate N and PE lines. A surge protector is only needed between the phase line and the PEN line.

The switch in front of the SPD can be either a fuse or a circuit breaker. Generally, a 40~63A breaker should be chosen for Imax>40kA, and a 20~32A breaker should be chosen for Imax<40kA.


Are surge protectors and lightning arresters the same thing?

While both surge protectors and lightning arresters serve to prevent overvoltages, especially those caused by lightning, there are several differences in their applications.

Lightning arresters come in multiple voltage levels, from low-voltage 0.38kV to ultra-high-voltage 500kV, while surge protectors are generally only available as low-voltage products;

Lightning arresters are often installed on primary systems to prevent direct invasion by lightning waves, while SPDs are mostly installed on secondary systems as supplementary measures after lightning arresters have eliminated the direct invasion of lightning waves, or when lightning arresters have not completely eliminated lightning waves;

Lightning arresters are used to protect electrical equipment,while surge protectors are mainly used to protect electronic instruments or meters;

Since lightning arresters are connected to primary electrical systems, they need to have sufficient external insulation performance and are generally larger in size. On the other hand, surge protectors, being connected to low voltage systems, can be designed much smaller.

So, while both serve to protect systems from overvoltage, their applications, design, and use cases can differ significantly. It’s essential to understand these differences to ensure you use the right device for your specific needs.

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