The magazine of Friedhelm Loh Group

The magazine of Friedhelm Loh Group

AX plastic enclosures from Rittal

Keeping tunnels lit in an emergency

Speeding into a tunnel at 300 km/h in an ICE (InterCity Express) train is always an experience. Even though the train is well sealed, you can still feel the pressure wave. A tunnel’s safety technology needs to withstand huge stresses, as does the equipment powering the emergency lighting. In the event of a power failure, this equipment ensures the emergency lighting operates reliably so that rescue teams and escaping passengers can find their way. The demands on the enclosures used are high. Safety technology manufacturers such as HERMOS Systems must also be able to provide proof of this reliability with appropriate certificates.

Text Ralf Steck ––– Photography

How does an emergency lighting system withstand extreme conditions? And how can its long-term functionality be ensured?

Passengers have been gazing out of the train window as they speed past picturesque landscapes. Suddenly, everything goes black. It’s a tunnel, but not quite as dark as they think – thanks to HERMOS Systems GmbH. This company is responsible for much of the safety lighting in the tunnels of Deutsche Bahn’s rail network in Germany. “We have now installed around 25,000 enclosures in Deutsche Bahn tunnels,” reveals Veit Demel, Managing Director of HERMOS Systems GmbH, giving an indication of the scale of the task. “They are fitted in pairs to create an emergency lighting power supply unit,” he adds. Battery-powered emergency lighting systems are installed in the tunnels in sections 16 metres long. Every power supply unit is connected to two sections and, if the power fails, will therefore light up 32 metres of tunnel so that escaping passengers and rescue teams can find their way. One enclosure houses the battery, while the other accommodates the electronics that continuously monitor and control the power supply units. Up to six of these emergency light power supply units are connected via a tunnel power distributor to a master cable. HERMOS uses Rittal AX standard enclosures to house these and other distributors. “As we see it, the enclosures need to meet two key requirements,” explains HERMOS Authorised Representative and Project Leader Robert Berndt. “Firstly, they must be robust and certified as complying with the provisions stipulated by the customer. And ­secondly, they must be available over a period of many years, because any change to our products – such as a new enclosure model – entails a lengthy and costly recertification process by Germany’s ­Federal Railway Authority,” he continues.

Safely protected: AX plastic enclosures house the technology.


The demands are high, especially when the enclosures are installed in high-speed rail tunnels. In some cases, ICEs travel through these at speeds of over 300 km/h, creating a huge pressure front ahead of the train and a vacuum behind it. If trains pass each other in a tunnel, the pressure conditions become even more challenging. “Strange as it may sound, only 95 percent of tunnel sections are underground,” explains Berndt. “In the portal area, the enclosures we use are installed in the open air, meaning they are exposed to the weather and to temperatures of between −20 and +40 degrees Celsius. Although temperatures are mostly constant inside the tunnels, conditions are very damp,” he adds.

The ability of enclosures to withstand these environmental conditions over a period of many years isn’t the only important consideration for HERMOS, though. The company also requires certificates guaranteeing compliance with the relevant standards. In some cases, the certification process is very extensive. For example, suction and pressure resistance is tested in the same kind of wind tunnel that is used in automotive engineering. Rittal has these tests carried out on its products and supplies the necessary certificates.

300 km/h

and above is the speed of ICE trains in tunnels

−20 to + 40º

temperatures and high humidity are typical in tunnels


pressure front ahead of the train and vacuum behind it


“We have been using plastic enclosures from Rittal since 1999, because they come with all the certifications we are required to submit to the Federal Railway Authority to obtain approval for our products. That means an important part of the approval process is completed quickly – we can simply forward the certificates supplied by Rittal and rely on the enclosures performing as specified in the standards,” says Demel.

Long-term availability is also ensured. The recently launched series of AX plastic enclosures is just the third enclosure generation for which HERMOS has needed to obtain certification in a period spanning almost 25 years. “Any change to the products necessitates recertification by the Federal Railway Authority. Besides time-consuming checking of documentation, that also involves a one-year practical test. If we don’t have at least one year’s notice before a change in the supply range, we therefore face a lengthy period during which we can no longer supply products to customers,” explains Berndt.



    1. Full outdoor capability thanks to high UV resistance and UL F1 outdoor rating (UL 746C)

    2. Personal safety ensured thanks to protective insulation (DIN EN 61140 protection class II)

    3. High protection category up to IP66 and NEMA 4X

    4. Internal components can be screwed directly into place

    5. UL approval for industrial enclosures

    6. Made of halogen-free material: no corrosive or toxic gases are produced in case of fire

    7. Tested for suction and compression strength


With its new plastic enclosures, Rittal offers an ideal solution for outdoor applications. Made from halogen-free materials, they do not emit any corrosive or toxic gases in the event of a fire. They also boast fire protection corresponding to the UL 94 V-0 standard, an UL F1 outdoor rating, UL approval for industrial enclosures, a protection category up to IP66/NEMA 4X for the encapsulated space, and class II protective insulation.


Thanks to its robust design and stable construction, the AX series withstands aggressive environments, damp conditions and pressure/suction forces. The sensitive electronic circuits inside the enclosures are also ideally protected against flying debris. Numerous mounting bosses in the enclosure ensure the interior fit-out can be customised on a 25 mm pitch pattern, for example using punched sections and rails. Initial experiences with the AX series have been good, as Berndt explains: “The AX enclosures are even more robust than their predecessors. For example, the locks and hinges are made from metal rather than plastic, which also creates a higher-quality feel. We initially tested a special enclosure with two locks due to the high pressure and suction forces, but it turned out that a standard series enclosure with one lock withstands these stresses just as effectively. That’s naturally far more economical and simplifies the supply process,” he emphasises. In addition, the mounting points for the AX series are much more solid than those of the predecessor model. Instead of eight screw fixings, four fastening points are now sufficient to hold the enclosure securely in place, whatever the stresses. “Only having to tighten half the number of screw fixings significantly shortens the installation time,” says Berndt.


The ability to deliver is an equally important aspect for HERMOS when selecting a supplier, because the timeframe during which fitters can install the products in a tunnel is very tight. “Tunnel construction is tightly synchronised. We often work around the clock and only have a few days for installation. That means equipment needs to be ready on time – a real challenge when several hundred enclosures are being installed in a tunnel. Rittal reliably delivers its products within eight weeks, a timescale that doesn’t pose a problem given that we plan a long way ahead. Delivery reliability is more important to us than a lead time one day shorter,” explains Demel. “We have been using the plastic enclosures from Rittal since 1999 and have had nothing but good experiences with them. That’s important, because you can’t just ‘nip into’ a high-speed tunnel to rectify a defect – you need to be able to rely completely on the components you use. Robust products, comprehensive certifications and excellent delivery reliability are the key factors that also help ensure the success of our company,” he concludes.

  • HERMOS Systems GmbH

    HERMOS Systems GmbH has been offering engineering services for automation technology in industry, building technology and infrastructure systems for 25 years. Not tied to any particular manufacturers or products, the company offers open solutions and standards. Its portfolio includes programmable controllers, project planning, and the creation of networks and software solutions for control rooms, including the necessary hardware. The parent company HERMOS AG supplies software such as FIS, a vendor-independent platform for the integration of technical plants.


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