RAC-Funkenstreckentechnologie - schont Endgeräte
RAC spark gap technology

Protects sensitive equipment

RAC = Rapid Arc Control: spark gap technology that limits mains follow current and is gentle on terminal devices


The RAC spark gap installed in DEHNshield ZP reacts extremely quickly and impresses with minimal residual energy*.

This means maximum safety and optimum care for downstream electronic terminal equipment, since such equipment usually only has minimal resistance to overvoltages. The service life of the terminal equipment in the protected area (10 metres of cable length) of the DEHNshield ZP is significantly extended, and also the service life of the arrester itself.

The advantages of arresters with RAC spark gap technology compared to combined arresters commonly available on the market with a series connection consisting of a varistor and gas discharge tube are shown in the minimal residual energy.


*Residual energy is defined as the value of a surge which enters the building, is absorbed by the surge arrester and is passed on to the downstream electrical and electronic devices and systems.

Wave breaker function

The basic property of the RAC spark gap technology is the wave breaker function.

If lightning strikes the installation, high impulse currents and impulse voltages appear in electrically conductive systems – similar to a huge tidal wave.

This wave destroys sensitive electronic consumers or systems if it is not broken. Here, a powerful combined arrester with RAC spark gap technology acts like a wave breaker. It breaks the incoming energy down to an acceptable level for the terminal equipment.


This means:

  • Protection of sensitive electronic devices

  • Preservation of downstream type 2 or type 3 arresters 

  • Extended service life of terminal equipment

Benefits of RAC spark gaps

The less residual energy let through by a surge arrester, the longer the service life of the terminal equipment.

RAC spark gap technology

residual energy rac spark gap

When arresters have this technology, the majority of the energy flows through the RAC spark gap.

This is gentle on the terminal equipment, since such equipment can only withstand minimal residual energy for a very short time. Its service life is therefore extended substantially.

Varistor technology

varistor residual energy

With varistor technology, a low proportion of the energy flows through the arrester or the arrester combination. In this case, significantly higher residual energy is applied to the terminal equipment over a longer time period.


Blue curve = total current; red curve = current flowing through the terminal equipment

How a spark gap with RAC technology works

The discharge process in three phases:

Phase 1

RAC-Funkenstreckentechnologie Phase 1 Zündung


Quick response and reliable discharge: the residual energy is kept to a minimum.


In phase 1, the electric arc is in the ignition area of the electrode.
The technology independently, reliably and quickly detects an arising lightning or surge event and starts the discharge process with the initial ignition.


Good to know: even the highest energy influxes (e.g. from direct lightning strikes) are safely discharged. At the same time, the RAC technology used ensures the lowest residual energies,  so downstream systems and terminal devices are reliably protected from the very first impulse. The fast reaction time reduces the load on the spark gap which considerably increases its service life.

Phase 2

RAC-Funkenstreckentechnologie Phase 2 Gegenspannung

Counter-voltage generation

Arc voltage and counter-voltage are further increased.


In phase 2, the electric arc is channelled into the arcing chamber. It should be interrupted as quickly as possible.

Options for quenching an electric arc:

  • The current flow is interrupted (e.g. by an upstream fuse). 
  • an arc voltage is generated which is greater than the mains voltage.

The problem: directly in front of the arcing chamber, the counter-voltage for the necessary follow current limitation or arc quenching is not yet high enough.

Phase 3

RAC-Funkenstreckentechnologie Phase 3 Löschkammer

Quenching process

Fast quenching ensures the lowest-possible loading of the upstream fuse devices.


In phase 3, the impulse is split up into several small partial electric arcs.


Due to the high number of partial electric arcs, the arc voltage increases strongly. As a result, the arc voltage is higher than the mains voltage.
The mains follow current present is heavily limited and quickly interrupted.


This extremely fast interruption ensures that the upstream fuse devices are burdened only to a limited degree.


In general, type 1 + 2 + 3 combined arresters from DEHN protect terminal equipment within 10 m of cable length.

This is where arresters with an RAC spark gap with extremely low residual energy impress. When compared to combined arresters commonly available on the market with a series connection consisting of a varistor and gas discharge tube, this is where their strengths are demonstrated.

Minimal residual energy means that terminal equipment is burdened only to a limited degree and thus well preserved.

The advantages at a glance


  • Discharge prevents damage to terminal equipment

  • No premature ageing of the terminal equipment

  • Less work involved with and lower costs for maintenance and replacement


RAC spark gap technology:

Fast, reliable, gentle – extra performance!


Have you got any questions? Contact us.

Technical support

Phone: +49 9181 906 1750

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