Surge arrester

A modular surge protective device (SPD) limits transients of atmospheric or network-switching origin. It comes in three types depending on exposure level: type 1 for sites with a lightning rod, type 2 for overhead networks, type 3 for fine protection downstream of sensitive equipment. Nominal discharge current In and maximum discharge current Imax are expressed in kA, with polyamide housings and plug-in cartridges compliant with the IEC 61643-11 and NF C 15-100 standards.

Types of surge protective devices and electrical protection levels

Type 1 SPD: protection against direct lightning strikes

A type 1 SPD is required when the building has a lightning rod or a lightning-capture system. It absorbs the partial lightning current with a high nominal discharge current In. Our installation experience confirms that positioning it at the head of the installation, upstream of the main circuit breaker, is the most effective configuration for protecting the whole electrical panel.

Type 2 SPD: protection of overhead networks and switching overvoltages

The type 2 SPD is used in sub-distribution boards or at the head of the installation when the network is overhead and exposed to inductive overvoltages. It complements a type 1 SPD when one is already present, or provides protection on its own in less exposed areas. We frequently see this device in rural or peri-urban installations where LV lines are carried on poles.

Type 3 SPD: fine protection of sensitive equipment

The type 3 SPD provides fine protection immediately downstream of sensitive equipment such as automation systems, IT servers or measurement systems. Its discharge current Imax is lower than that of types 1 and 2, but its response is optimised for low residual voltages. Our installation feedback shows that combining it with an upstream type 2 SPD is the most complete solution for design offices and SMEs.

Modular design and ease of maintenance of surge protective devices

Plug-in cartridge with end-of-life indicator

The plug-in cartridge fitted to our modular SPDs includes an end-of-life indicator visible without dismantling. This design allows the worn cartridge to be replaced without any work on the existing wiring, significantly reducing installation downtime. Feedback from installers confirms that this feature is particularly appreciated on sites where continuity of service is critical.

Standardised DIN-rail mounting in the electrical panel

The polyamide housing of SPDs provides satisfactory mechanical strength in an electrical panel environment. DIN-rail mounting standardises integration into enclosures and panels of any brand, whether at the head of the installation or in sub-distribution boards. We recommend checking the available module width, generally 1 to 4 modules depending on the rating and type of SPD.

Compliance standards and sizing of surge protective devices

Application of the IEC 61643-11 and NF C 15-100 standards

The IEC 61643-11 standard defines the requirements and test methods for low-voltage SPDs for distribution networks. NF C 15-100 sets the rules for their implementation in French electrical installations, including mandatory location according to the building's Lightning Protection System (LPS) level. Our standard practice favours strict compliance with both references to guarantee insurance coverage and personal safety.

Rating selection according to discharge current In and Imax

Sizing an SPD is based on the nominal discharge current In and the maximum discharge current Imax, both expressed in kA. Over-sizing leads to unnecessary purchase cost, while under-sizing reduces the device's service life and its effective protection. In the field, we find that precisely assessing the site's exposure level, in line with the UTE C 15-443 guide, helps to optimise this technical and economic choice.

Frequently asked questions

What is the difference between a type 1 SPD and a type 3 SPD?

The type 1 SPD absorbs partial lightning currents at the head of the installation, while the type 3 SPD limits residual voltages immediately downstream of sensitive equipment. Combining them in cascade provides complete protection in line with NF C 15-100.

How can you tell that an SPD cartridge needs to be replaced?

The end-of-life indicator built into the plug-in cartridge changes visual state once the internal varistor has reached the end of its endurance. This visual check is carried out without dismantling, during regular maintenance visits to the electrical panel.

Is a type 2 SPD sufficient without a type 1 SPD in an urban area with an underground network?

In urban areas with an underground network and no lightning rod, a type 2 SPD at the head of the installation may be sufficient, depending on the lightning-risk analysis. Nevertheless, installing a downstream type 3 SPD is still recommended for fine protection of IT and automation equipment.

Are modular SPDs compatible with all DIN rails?

The polyamide housings of SPDs are designed for the 35 mm symmetrical DIN rail compliant with EN 60715. This standardisation guarantees compatibility with all enclosures and electrical panels on the market, regardless of brand.