The magazine of Friedhelm Loh Group

The magazine of Friedhelm Loh Group

UL standards for enclosure construction
Experience – Engineering

With Rittal fit for the US market

Switchgear engineering. Different markets, different standards. While it’s the IEC that sets standards in Europe, in the US market, it’s the standards of UL and the NEC that need to be observed – and they are much stricter. For plant engineers such as ATR that export to North America, ensuring compliance is no easy task. They need expertise and skilled partners, such as Rittal.

Text Dr. Jörg Lantzsch and Hans-Robert Koch ––– Photography

Done! Stephan Rabsch sticks the badge with the UL logo onto the enclosure: “That is the very last step before we deliver the switchgear to the US market,” explains the head of production at control system and switchgear engineering firm ATR Industrie-Elektronik. The badge indicates that the unit is standard-compliant and is a green light for a problem-free sign-off in the USA. “The UL logo on the finished switchgear makes on-site sign-off so much easier,” explains Rabsch.

That is an extremely important point, particularly when you’re talking about a total of 150 m of enclosures, which is the current plant size. Added to that are hundreds of operating housings and terminal boxes. This particular switchgear is destined for a fibreboard manufacturing plant in the USA that ATR’s parent company – the Siempelkamp Group – is setting up in Barnwell, South Carolina. The plant, which will produce up to 280,000 m3 of fibreboards a year once operational, is the largest order the Siempelkamp Group has ever had. As the switchgear engineer for all Siempelkamp companies, ATR is supplying the switchgear for the relevant plant elements. The timing is tight. “A very tight timeframe is typical for orders from the USA,” points out Timo Amels, Managing Director: “There’s a maximum of one to one and a half years from getting the order to starting up the plant.” An important part of that process is ensuring the final acceptance of the plant by UL goes through smoothly.


“We can do UL – and, thanks to the excellent delivery availability from Rittal, we can provide the punctuality we promise our customers.”

Timo Amels
Managing Director at switchgear engineering company ATR Industrie-Elektronik

Engineering UL-compliant switchgear requires special expertise. Indeed, the standards and the way in which plants in the USA have to be signed off differ from the approach used in Europe – sometimes considerably. Unlike IEC standards, which merely specify the minimum safety requirements for a device or system, the UL standards for the US market go into more detail in many instances. Before they are started up on site, plants must be signed off and approved by an inspector, known as the AHJ (authority having jurisdiction). The AHJ checks and certifies a whole range of materials, components and final products to ensure their operational reliability and safety. In the case of UL, there is a stronger focus on personal and fire safety, although equivalent IEC and UL standards also differ in terms of technical details. The clearance and creepage distances are slightly larger under UL stipulations and the NEMA type needs to be stated instead of the IP protection category. Another typical detail of switchgear to UL standards is the locking mechanism of the enclosure, which must ensure the enclosure doors cannot be opened while the system is live.


Speeding things up with UL self-certification

ATR is part of the UL Listed Panel Shop Program. This means that UL certifies the switchgear engineer at regular intervals and thus ensures the company has – and applies – the necessary expertise to ensure its switchgear complies with the standards for the US market. “Thanks to close cooperation with UL, we can rest assured we are always up to date when it comes to the latest standards,” says Rabsch. The in-house plant standards at ATR largely correspond to UL508A, which gives the switchgear engineer an edge on the competition, as Amels points out: “We are permitted to self-certify our systems to UL standards and apply the corresponding label. That saves us a huge amount of time.” Companies that are not part of the UL Listed Panel Shop program have to have their switchgear certified externally – and that takes time and money.

UL-listed components

Besides knowing how to engineer a plant that satisfies UL standards, it is crucial that all the components used are – as far as possible – already listed or recognised by UL. That is one of the reasons why Rittal is one of ATR’s preferred suppliers. For example, the TS 8 series enclosures and busbar systems are UL-listed. The climate-control components and other parts such as the new enclosure lights are also UL-listed and can therefore be used without any problems. The relevant Siempelkamp company undertakes the engineering and electrical planning work for the switchgear and supplies the information to ATR. “We are practically a qualified contract manufacturer,” says Amels, explaining the switchgear engineering company’s strategy: “That’s the way we do things with external customers, too, in other words our customers from outside the Siempelkamp Group, which currently account for 40 percent of our sales.” Electrical planning work is completed almost exclusively in Eplan Electric P8 before being supplied to ATR. If the switchgear needs to satisfy UL508A, ATR first checks whether the planning has been carried out accordingly. Customers who have no experience with UL are given appropriate advice so they can adjust their planning to use UL-listed components, for example.

Just-in-time deliveries

The strengths of ATR lie not just in its extensive expertise, but also in the company’s high productivity. If all the enclosures it manufactures in the space of a year were lined up, they would stretch for more than 6.5 kilometres. “We stand out from the competition thanks to our international alignment and absolute dependability when it comes to deadlines,” says Amels. However, all that also depends on optimum collaboration with suppliers. For example, the just-in-time deliveries from Rittal are crucial to the smooth running of production. Twice a week, a huge semi-trailer truck arrives with enclosures, housings and other components. A dedicated on-site intermediate storage warehouse provides additional flexibility. “It is also thanks to the excellent delivery availability from Rittal that we can provide the punctuality we promise our customers,” says Amels.

The team at ATR are already working on the future of switchgear engineering – and digitisation is taking centre stage. One of their aims is to ensure consistent data management. “The data on Rittal products that is provided on the website and in the Eplan Data Portal is accurate and complete,” points out Rabsch: “That makes lots of the work we have to do easier – from planning through to documentation.”

Consistent data management

The company is already planning automatic cable routing based on engineering plans, during which cable lengths are automatically calculated. This also requires absolute consistency in data management. In future, ATR aims to make a growing number of processes throughout the value-added chain paper free. That is already the case for documentation. To make wiring paper-free, the company plans to use tablets in planning work. “I don’t want my staff to have to check off paper circuit diagrams during wiring work,” explains Amels, setting out his vision for the future of switchgear engineering.


“The data on Rittal products that is provided on the website and in the Eplan Data Portal is complete. That makes lots of the work we have to do easier.”

Stephan Rabsch
Head of production at switchgear engineering company ATR Industrie-Elektronik

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