The task of enclosures is to protect electronic components from external influences so that buildings, industrial facilities and critical infrastructure can operate reliably. To ensure electrical systems carry on working, even in the event of a major earthquake, enclosures need to be designed to withstand the associated stresses and strains. In this blog, we explore the key considerations when selecting an earthquake-resistant enclosure and the technical standards that need to be complied with.
Earthquake-related damage to electrical systems
One very important point to make before we start is that an earthquake-resistant enclosure is not enough on its own to guarantee an electrical system will remain up and running during and after an earthquake. Given the enormous natural forces that are unleashed, the surrounding building structure and the components installed inside must also be designed for these special requirements. The housing does play a key role, though, because if the enclosure fails to withstand the earthquake, the entire electrical system will stop working.
Types of earthquake-related damage
Depending on the magnitude of an earthquake, an electrical system can sustain various types of damage – from malfunctions that are easy to repair through to structural damage that means the entire system needs to be replaced.
| Type of damage | Description of damage | Result of damage |
| Malfunctions | Individual electrical contacts coming loose or short-circuits interrupted by available safety equipment. | Short-term consequences – simple repairs can get the system back up and running. |
| More extensive damage | Electronic components detaching from support rails or mounting plates. | Medium-term consequences – if the components cannot be reattached, damaged parts need to be replaced. |
| Structural damage | The enclosure being moved by the earthquake, potentially being separated from its floor anchoring, overturned or damaged from the outside. | Long-term consequences – the entire enclosure may need to be replaced. |
Technical standards relating to earthquake resistance
To ensure enclosures are protected as effectively as possible from the short- to long-term consequences of an earthquake, knowledge of the key technical standards in this field is vital. The following three standards are especially relevant for enclosure manufacturers:
| Standard | Content |
| DIN EN/IEC 60068-3-3 | Describes seismic test methods for electrical equipment and, for example, specifies ways of simulating earthquakes. |
| IEEE 693 | Standard relating to the seismic qualification of substations. Defines test methods and design guidelines for entire substations. Also includes regulations for building structures, foundations and the floor anchoring of enclosures. |
| Telcordia GR-63-CORE | Not a technical standard as such, but invitations to tender in the USA often stipulate it must be complied with. It is based on the USA’s regional split into earthquake risk zones (0 to 4, where 0 = low risk and 4 = high risk) and defines comprehensive requirements relating to the physical robustness of enclosures. This includes maximum resistance to earthquakes, but also to humidity, fire and contaminants. |
Enclosure testing on a shaker table
One thing all three standards have in common is the method they specify to prove enclosures are suitable for use in earthquake-prone areas. Enclosures are subjected to vibrations and shocks on a shaker table and then checked for structural damage. A particular enclosure model is only deemed to be earthquake-resistant if there is no resulting damage to its load-bearing parts, fastenings, doors, hinges or locks. Although the details of shaker table testing differ between the three standards, Zone 4 certification (the highest risk level) in line with GR-63-CORE in the USA covers almost all the requirements of the other two standards.
Stability – features that make an enclosure resistant to earthquakes
When it comes to making enclosures that will survive the shaker table test and, if need be, an actual earthquake intact, the principle that triangles are stronger than squares has proved itself in practice. In a similar way to how trusses are used in architecture, the rectangular outer frames are created using multiple struts that form triangles. Since this means the struts are almost exclusively subject to compressive and tensile forces, the entire structure has an extremely high load-bearing capacity.
Accessories for maximum earthquake resistance
The Rittal earthquake kit applies this particularly earthquake-resistant design principle to VX25 large enclosures. This extension kit comes with additional struts for the sides of the enclosure to divide the rectangular outer frame into a number of triangles. The kit also includes special gusset plates to further reinforce the corners of the frame. These accessories strengthen the enclosure sufficiently to meet even the most demanding requirements relating to suitability for use in earthquake-prone areas. It is also possible to install a more stable, earthquake-resistant base/plinth that fixes the enclosure to the floor securely enough to withstand earthquakes.
Tip: In earthquake-prone regions, it is advisable to bay enclosures. This can increase the level of rigidity.
Which measures achieve which level of earthquake resistance?
| Enclosure | Measures | Tested installed weight in kg | Level of earthquake resistance |
VX25 800 x 2000 x 600 mm | Standard enclosure
Comfort handle Side panels Base/plinth (2024) | 200 | Telcordia GR-63-Core Zones 1 & 2 (2g peak between 2 and 5 Hz) |
VX25 800 x 2000 x 600 mm | Standard enclosure
Comfort handle Side panels Base/plinth (2024) | 200 | Telcordia GR-63-Core Zone 3 (3g peak between 2 and 5 Hz) |
VX25 800 x 2000 x 600 mm | Standard enclosure
Comfort handle Side panels Earthquake-resistant base/plinth Earthquake kit | 500 | Telcordia GR-63-Core Zone 4 (5g peak between 2 and 5 Hz) |
Summary
Enclosures for earthquake-prone regions must meet special requirements. Knowledge of the relevant technical standards is therefore recommended, along with use of specially certified enclosure models. Ultimately, however, the specific project requirements will always determine the complexity of building an enclosure that is suitable for use in earthquake-prone areas. Especially when the entire electrical system needs to continue working properly, simply relying on previously tested enclosure models is inadequate. Each enclosure must be tested separately in such cases, including its installed components.
| Requirement | Implementation | Result |
| Structural integrity of enclosure is maintained | Use of previously tested enclosure models | Lower outlay and shorter time-to-market |
| Entire electrical system remains operational | Each enclosure must be tested separately, including its installed components. | Higher outlay and longer time-to-market |
FAQs
1. Why is earthquake resistance important for enclosures?
Enclosures protect key power distribution and control components. If an enclosure fails to withstand an earthquake, there is a risk of malfunctions, components coming loose and/or structural damage. This can mean the entire electrical system stops working.
2. What types of enclosure damage can an earthquake cause?
Earthquakes can cause malfunctions (e.g. due to contacts coming loose), more extensive damage (e.g. components coming loose) or even structural damage if the enclosure moves, is detached from its floor anchoring or is damaged in some other way.
3. Is an earthquake-resistant enclosure sufficient on its own?
No. To keep the entire system working properly, the building structure and the components installed inside the enclosure must also be resistant to earthquakes. A stable enclosure housing is important, but only part of the overall protection strategy.
4. What technical standards are relevant for earthquake-resistant enclosures?
Key standards are DIN EN/IEC 60068‑3‑3 (seismic test methods), IEEE 693 (qualification of substations, including building anchoring) and Telcordia GR‑63‑CORE (robustness requirements based on Earthquake Zones 0 to 4). GR‑63‑CORE Zone 4 covers most requirements of other standards.
5. How is an enclosure’s suitability for use in earthquake-prone areas tested?
Testing is carried out on a shaker table that simulates vibrations and shocks. The enclosure is deemed to be earthquake-resistant if no load-bearing parts, doors, hinges or fastenings are damaged.
6. What accessories further increase earthquake resistance?
Rittal offers an earthquake kit for the VX25 that includes additional struts and gusset plates. The accessories making up this extension kit reinforce the frame and enable certifications up to GR‑63‑CORE Zone 4. An earthquake-resistant base/plinth with enhanced stability can also be used to ensure secure anchoring to the floor.
Dr. Dirk Pieler
Executive Vice President Business Unit Industry Solutions at Rittal
With his many years of industry experience, Dirk Pieler is helping to advance the digital transformation and automation in enclosure manufacturing.