ACI technology – surge protection without external backup fuses for switchgear

For reliable and long-lasting protection of your systems.

A single instance of surge damage can result in data loss, downtimes and high follow-up costs. DEHN's innovative Advanced Circuit Interruption (ACI) technology reliably protects systems from precisely such problems by combining surge protection with a backup fuse in a single module.

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Advantages of ACI technology

Simple and reliable planning

ACI works without an external backup fuse, reducing complexity, wiring and installation costs. At the same time, the technology minimises thermal energy input during shutdown, which protects adjacent cables and components, reduces insulation ageing and increases the overall service life of the installation.

Integrated, maintenance-free and available

Surge protection and backup fuse are combined in a coordinated system – meaning fewer components and no coordination errors. ACI remains permanently operational after incidents and is completely maintenance-free. Unscheduled downtimes are avoided and inspection costs are significantly reduced. Status messages via integrated signal connections can be easily integrated into existing monitoring systems.

Thermal and electrical stability

Series of measurements show that ACI arresters maintain their protection level and contact resistance even after repeated tripping. The stable spark gap geometry prevents material migration and contact welding – typical weak points of conventional systems. Protection remains constant over the long term, even with changing temperatures or network conditions.

System availability

ACI provides a consistent level of protection even during repeated transient events. The modules are TOV-proof up to 442 V AC and can withstand temporary overvoltages without entering a critical state. This ensures stable, reliable operation when subjected to real fluctuations in the grid.

Space-saving and standard-compliant

The elimination of external fuse holders reduces the space required in the switchgear cabinet, shortens cable routes and reduces costs. ACI has been certified as compliant with DIN VDE 0100-534 and EN 61643-11, so it meets all the requirements of the relevant standards.

ACI means safety at the highest level

Extreme short-circuit conditions occur in industrial plants, switchgear assemblies, or power stations. This is precisely where ACI technology demonstrates its strength. It reliably disconnects even at high fault currents and ensures that no residual currents flow after a surge event.

In conventional solutions with separate fuses, the additional conductor between the SPD and the backup fuse causes induction peaks that can increase the protection level. ACI completely eliminates this conductor. The spark gap combination is precisely matched to the arrester, eliminating the need for a backup fuse.
The residual voltage level is reduced, even under repeated load.
A conductor cross-section of just 6 mm² Cu is always enough. You save the valuable time you would, in the past, have spent dimensioning the cross-sections. Installation is also easier because 6 mm² Cu means smaller radiuses and shorter wiring.
Long-term tests confirm the stability of the modules over thousands of switching cycles.
All our ACI modules are tested in accordance with EN 61643-11 (Type Test A). The test sequences include short-circuit, TOV and follow current tests, which simulate switching performance under real grid conditions.

Conventional solution, CI or ACI: What are the differences?

The protection mechanism used determines installation effort, safety and overall performance. CI and ACI devices replace the traditional combination of SPD and external fuse: CI integrates a fusible link, while ACI provides exceptionally fast, selective and leakage‑current‑free disconnection without any additional fuse.

For you, this means fewer components, clearer protection structures and a robust, future‑proof solution for a wide range of applications.

Feature	Conventional Solution (SPD + External Fuse)	CI Devices	ACI Devices
Backup protection (fuse)	External fuse required, installed upstream of the SPD	Integrated (fusible link)	Integrated (spark‑gap‑based disconnection mechanism)
Backup protection (fuse)	External fuse required, installed upstream of the SPD	Depends on the rating of the integrated fuse	Integrated (spark‑gap‑based disconnection mechanism)
Cross‑section of connecting conductors	Depends on the rating of the external fuse	Depends on the rating of the integrated fuse	6 mm² for Type 2 16 mm² for Type 1
Leakage‑current‑free operation	Only with spark‑gap‑based SPDs and gas discharge tubes	Only with spark‑gap‑based SPDs and gas discharge tubes	Always ensured due to ACI technology
Disconnection time in case of fault	Depending on the failure scenario and fuse rating – a few milliseconds up to seconds	Depending on the failure scenario and fuse rating – a few milliseconds up to seconds	Within a few milliseconds, independent of the fault current level
Selectivity of backup protection	Requires precise selectivity coordination with the upstream fuse	Limited selectivity due to integrated fusible link	Selective operation with small installation fuses always ensured
TOV withstand	Depends on the SPD technology used (varistor, gas discharge tube, spark gap)	Depends on the surge‑protection element used (varistor, gas discharge tube, spark gap)	Additional galvanic isolation increases TOV withstand capability

Areas of application for ACI technology

Thanks to its integrated design, ACI also meets the requirements of DIN VDE 0100-534, which stipulates a maximum conductor length of 0.5 m between the surge protection and backup fuse.

Switchgear

with limited space or complex distributions

Industrial automation systems

with sensitive sensor technology

open field photovoltaic system with sunset in the background

PV and energy systems

in which DC-side surge protection is required

Building technology

with high demands on system availability

Relax. It is DEHN ACI technology.

Forget about that time-consuming dimensioning of the backup fuse! Our Type 1 and Type 2 arresters with ACI technology have an integrated switch/spark gap combination. This reduces errors, enables flexible installation and raises system availability to a new level.

Further details on the ACI arresters from DEHN can be found on the respective product pages:

Type 1 DEHNventil ACI arrester

Type 2 DEHNguard ACI arrester

Type 2 DEHNguard M DC ACI arrester