Content

overview of standards

Theory & Practice

protected areas in Cabinet and base

THE CORRECT USE OF BASE PLATES


overview of standards

The cabinets manufactured by ELSTA are primarily intended to be used as enclosures for assemblies according to IEC 61439.
This standard specifies the following minimum degrees of protection for the housing of the assembly (with closed doors).

Minimum degrees of protection for the housing of the assembly with closed doors (according to IEC 61439):

PRODUCT STANDARD vs. TEST STANDARD FOR IP PROTECTION degrees

IP degrees of protection are tested and evaluated in accordance to the standard IEC 60529.
More information can be found here: IP protetction rating in accordance with IEC 60529

The test is carried out regardless of the product standard.

The product standards for specific switchgear assemblies (IEC 61439) define minimum requirements for the IP protection degree for the different product groups.

The standard for empty cabinets (IEC 62208) only requires a test-based verification of the protection class specified by the manufacturer.

The evaluation of the test result depends on the application, however. Consider for instance the IPX4 and IP5X classification: the spray or jet water generated for the X4-test, as well as the swirled dust in the chamber for the 5X-test, must not penetrate the protected space to more than an admissable extent. The extent depends on the components to be protected and their position in the cabinet.

The test standard IEC 60529 therefore only defines general acceptance criteria and leaves it to the respective product standard to determine the permitted quantity.

IS THE IEC 62208 TEST STRICTER THAN IEC 61439?

Depending on the definition of the protected area  the test according to IEC 62208 can be stricter. It is actually decisive whether the insulation strength is disturbed by the penetration of dust and / or water. Therefore, the standards allow for energised IP-testing or insulation testing after applicating if agreed upon.

 

how does THE degree of PROTECTION relate TO THE DEGREE OF POLLUTIOns?

It can be assumed that the degree of external pollution is reduced by higher degrees of protection (1st digit) so that lower degrees of pollution occur in the interior of the enclosure. The degrees of pollution define, for example, whether dust is permitted as pollution. However, it depends on the environment whether the penetrating dust is / can become conductive or not.

Example: In part 4 of IEC 61439 (assemblies for construction sites, ACS) it is pointed out that the protection class IP5X can reduce the external degree of pollution (only degrees 3 or 4 are permissible for ACS) to degree 2 inside the enclosure if sufficient measures are taken against condensation. In any case, a cabinet with degree of protection IP44 reduces the degree of pollution on the outside from level 4 (includes rain) to level 3. By installing further separation, e.g. closed compartments for switching devices, a reduction to degree 2 within these compartments can be achieved.

 

THEORY & PRACTICE

LABORATORY CONDITIONS VS. REALITY

Standard test conditions for protection against spray water (IPX3) and splash water (IPX4) reflect real outdoor conditions only partially. During thunderstorms or strong winds, rain is rather comparable with jet water that hits the cabinet with pressure (as under test conditions for IPX5) than splash water. Therefore, water ingress after heavy rain or thunderstorms is possible in practice if IPX4 enclosures are used – even if water has not penetrated the enclosure during laboratory tests.

In standard outdoor cabinets with ground-mounted bases, water can – once ingressed – flow freely down the enclosure on designated paths (e.g. alongside the inner surface of the cabinet) and is able to run off into the ground, not causing any technical problems.
Another reason for the occurrence of water on the inside surface of outdoor enclosures is condensation of moist air. Usually, this does not cause problems, as long as water will run off the enclosure, so that permanently condensing microclimate does not occur.

Comparing IP44 to IP54: the second digit

Cabinets designed to protect not only against solid foreign bodies with a diameter of ≥ 1.0 mm (IP4X) but also against dust (IP5X), must be especially sealed to reduce the ingress of dust to an acceptable level. This sealing also causes better protection against water ingress, although they may achieve the same classification (e.g. IP54 compared to IP44). That means that IP54 enclosures provide a higher degree of protection than against the ingress of water required for IPX4, but IPX5 is not achieved.
However, sealing the cabinet also reduces the exchange rate of air moisture between the inside of the cabinet and ambient conditions, which leads to notably increased condensation. Thus, additional measures against condensate are often necessary. To avoid condensation totally, even higher degrees of protection (e.g. IP6X) with vapor-impermeable seals are necessary.

protected areas in cabinet and base

In general, the enclosed protected space, which is defined as the space that encloses equipment providing defined protection against external influences and contact with live parts, is within the limits of ​​the cabinet only (upper part). The base is a component and not an electrical component, so there are no defined requirements for a degree of protection.
What may sound surprising at first is easy to understand. The main focus of the national standardization was on the compatibility of cabinets and bases of various manufacturers.
Of course, an “imaginary” degree of protection can be determined.

The degree of protection including the base varies depending on the combination of base and cabinet series, as the following figure shows:

 

 

Explanations to the pictures:

It must be ensured that bare, dangerous live parts are only installed within the protected areas described, where they cannot be reached by poking (IPXXD). Particular attention should be paid to the recessed constrictions when using type “F” bases! In general, we strongly advise against bare live parts positioned in the base or extending into it. Other conductive parts such as earthing rails can also be safely installed in the base.

the correct use of base plates

Originally designed as distribution cabinets for public power grids, ELSTA enclosures are open at the bottom (towards the base) in order to provide the maximum cross section for cable entry.
According to IEC 61439 part 5, which deals with the technical requirements in more detail than corresponding national standards, the possibility of inserting connection cables from the front is required. This practically excludes the use of base plates or at least limits the design options of the plates.

The robustness of the installed equipment and the need for sufficient ventilation both speak against an excessively high degree of protection, which is why a degree of protection of IP34D is sufficient for PENDA-O installed in public areas in accordance with IEC 61439-5.

In practise, some applications require a protection of the cabinet against the base with a higher degree of protection, especially if IP54 cabinets are used.

ELSTA provides several solutions:

ELSTA HAS EXPERIENCE IN TESTING AND IN-HOUSE TESTING Equipment available to determine the deGree of protection.
contact us if you Need further assistance!
We will be glad to assist you in choosing the best Cabinet design for your application!


Sources:

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