How safe is your enclosure?
13 November 2015
Enclosures do not just provide protection for the electrical equipment installed inside them; they also protect the people who work in close proximity from the dangers posed by internal electrical faults. Phil Glenister reports.
The protection requirements and safety measures for switchgear and control gear systems vary according to installation site, industry and application and are set out in standards, regulations and licensing conditions.
The best-known requirements for enclosures are the IP protection categories set out in IEC 60529 for protection against ingress of particulates and moisture. However, there are also several other requirements relating to enclosures, including dimensional accuracy, corrosion resistance, dynamic material strength, and protection in extreme climatic conditions, among others.
These requirements, and the tests and verifications they involve, are set out in standards such as IEC 62208 and IEC 61439-1. However, it should be noted that additional certifications are required for certain markets (North America, Europe or Asia, for example). In North America, NEMA standards or UL certifications are needed for the verification of protective functions instead of IEC standards. For certain application areas, such as marine or rail, additional design requirements apply.
For certifications from organisations such as UL, Lloyds and DNV, production facilities are checked regularly following the initial assessment. If the audit is successful, these classification bodies grant permission for their seal of approval to be used on enclosures until the next inspection. Manufacturers that regularly undergo inspection by these organisations can therefore be relied on to provide consistent enclosure quality.
Enclosure manufacturer, Rittal has a test laboratory at its headquarters in Herborn that is accredited for a range of tests and can thus also serve as an important partner for other companies. In addition to the initial tests required for new products, the company also regularly tests the properties of enclosures in current production, in order to maintain quality standards.
Alongside regularly testing products for quality, having a standardised production process is also important for ensuring consistency. To ensure that this is maintained even when it comes to bespoke dimensions or specal enclosures, Rittal's approach to manufacturing is based on 'platform' technology. Special enclosures are therefore manufactured and coated in the same way and do not differ in terms of quality from products stocked as standard models.
More than just a lick of paint
A top quality enclosure makes use of the latest technology and fulfils the requirements set out in the relevant standards. For instance, corrosion protection involves more than just a layer of paint across the metal body.
Ensuring long-lasting corrosion protection requires a specific process made up of several different stages, from initial cleaning to a final powder-coating of the primed enclosure. Long-lasting corrosion protection is key to ensuring that electrical switchgear enclosures provide protection for both personnel and equipment even after many years in operation.
For electrical switchgear enclosures, corrosion protection is required by IEC 62208 and IEC 61439. The required corrosion test is conducted in accordance with IEC 60068-2. Depending on the testing standard, a distinction is made between indoor and outdoor installation. To verify corrosion resistance, the corrosion process (which actually takes place over several years) is simulated in just a few days using a salt spray test.
Rittal spray-finished sheet steel enclosures for indoor application meet the requirement for corrosion resistance thanks to a standardised coating process adopted by the company. Once initial manufacturing is complete, the enclosures are then cleaned and degreased to ensure the durability of the coatings to be applied.
Immediately after degreasing, the first corrosion protection coating is applied using nanoceramic pre-treatment. For the second coating, the enclosures are fully submerged into a dip tank and subjected to electrophoretic dipcoat priming.
Corrosion protection is completed with powder coating, which also provides the structure for the enclosure’s outer skin. If, at a later stage in the system’s operation, the outermost coating is damaged, there are still two further layers in place to prevent rusting.
One of the key protection objectives that IEC 61439 strives to promote is the safety of people who operate electrical switchgear systems or work in close proximity to them. The standard therefore includes several specifications for the mechanical properties of enclosures.
Electrical faults can place high demands on enclosures in the form of increased internal pressure or the magnetic effect of a high short circuit current. An increase in internal pressure can, for instance, be triggered by short circuit shutdown by large circuit-breakers that cause arcing when switched off.
Furthermore, the magnetic field that forms around a copper bar particularly during high short circuit currents has an effect not just on the neighbouring copper bar but also on parts of the enclosure, including the mounting plate.
It must be ensured that enclosure doors do not open during short circuit shutdown and that the busbar system remains secured even in the event of a short circuit. If an enclosure door is blown from its fixings and internal parts ejected, then there is a high potential for injury of people in the vicinity of the enclosure.
This is why it is important for an enclosure to maintain its original mechanical strength even after several years and not weaken due to rust or any other factors. Standardised production and coating processes are crucial to ensuring this long-term mechanical strength.
Phil Glenister is product manager, industrial & outdoor enclosures, Rittal
Contact Details and Archive...