D R I V E S & S W I T C H G E A R

The IEC 61439, the new standard for low-voltage (LV) switchgear and controlgear assemblies, was published in 2009 to harmonise and define all general requirements for LV electrical assemblies.

New standard for LV switchgear, controlgear assemblies

Only two parts of the standard are necessary to determine all requirements for each type of electrical assembly: the basic standard IEC 61439-1 General rules and the specific assembly standard. The current IEC 60439 The current IEC 60439 standard applies to enclosures with the rated voltages under or equal to 1000 V AC (at frequencies not exceeding 1000 Hz) or 1500 V DC. The standard makes a distinction between typetested assemblies (TTAs) and partially type-tested assemblies (PTTAs).The following parts are mentioned and have equal weighting. There is not a formal hierarchy. Each part is a complete entity and can be used on an individual basis: IEC 60439-1: Type-tested and partially type-tested assemblies. I E C 6 0 4 3 9 - 2 : Pa r t i c u l a r requirements for busbar trunking systems (busways). IEC 60439-3: Particular requirements for low-voltage switchgear and controlgear assemblies to be installed in locations where unskilled persons have access. IEC 60439-4: Particular requirements for assemblies for construction sites (ACSs). I E C 6 0 4 3 9 - 5 : Pa r t i c u l a r requirements for assemblies to be installed outdoors in public places cable distribution cabinets (CDCs) for power distribution in networks.
IEC 60439-1 +

Information from ABB

IEC 61439-2 IEC 61439-6 IEC 61439-3 IEC 61439-4 IEC 61439-5

replaces will replace will replace will replace will replace

IEC 60439-1 (still valid until 2014) IEC 60439-2 (still valid) IEC 60439-3 (still valid) IEC 60439-4 (still valid) IEC 60439-5 (still valid)

Table 1: The relationship between the two standards.

The new IEC 61439 The new standard applies to enclosures for which the rated voltage is under 1000 V AC (at frequencies not exceeding 1000 Hz) or 1500 V DC. The standard defines the design verified assemblies and eliminates completely the categories TTA and PTTA. To conform to the standard, type tests have been replaced by a design verification which can be carried out by the three following equivalent alternative methods: testing, calculation/measurement or application of design rules. The following parts are mentioned and do not have equal weighting. There is a formal hierarchy. Individual parts cannot be used individually: IEC 61439-1: General rules. IEC 61439-2: Power switchgear and controlgear assemblies. IEC 61439-3: Distribution boards. IEC 61439-4: Assemblies for construction sites.
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IEC 61439-5: Assemblies for power distribution. IEC 61439-6: Busbar trunking systems. Part 1 is the general rules part and cannot be used alone to specify an assembly. Part 2 defines the specific requirements of power switchgear and controlgear assemblies (PSC assemblies) and must be used with part 1. This is the only part that has a double role as it covers PSC ASS emblies and any assembly which is not covered by any other specific parts. Parts 3 X are still under preparation but are already mentioned in Part 1. These could total more than four as additional parts may be developed as the need arises. To summarise, with the currently used IEC 60439, the rule is one part for each type of assembly. With the new IEC 61439 the rule is two parts for each type of assembly. The compliance

Te s t s t h a t h a v e b e e n m a d e i n accordance with IEC 60439 which fulfill the requirements of the new IEC 61439 need not be repeated. The second stage verification is routine verification, performed to verify that the materials and workmanship are in accordance with the requirements of the standard. Routine verification replaces the current routine test. It is more detailed but, essentially, the new requirements are the same as in the IEC 60439. This verification must be carried out for each completed assembly and it is the responsibility of the assembly manufacturer (see Fig. 1). Additional verification New requirements from the standard IEC 62208: Empty enclosures for assemblies, have been added: Verification of resistance to UV radiation for outdoor plastic enclosures. Verification of corrosion resistance. M a n d a t o r y d e c l a r a t i o n a n d confirmation of an impulse rating. Lifting, mechanical impact and marking. Other changes

Fig. 1: Comparison between the current and the new verification flow.

of an assembly is declared referring to the specific assembly standard (e.g. IEC 61439-2), and the compliance with the general rules (IEC 61439-1) is always implicit. The phrase TTA switchgear according to IEC 60439-1 is now replaced by Power switchgear and controlgear assemblies according to IEC 61439-2, design verified assembly. The validity of the two standards will overlap until 2014, and prior to this date assemblies can be manufactured according to IEC 61439 or IEC 60439. The relationship between the two standards is shown in Table 1. Main changes The new IEC 61439 includes the following significant technical changes with respect to the last edition of IEC 60439. Responsibility split New terms have been introduced and there is a split in product responsibility between the original manufacturer (responsible for carrying out the original design and the associated verification of an assembly) and the assembly manufacturer (e.g. panel builder using an assembly system from an original manufacturer) assuming responsibility for the completed assembly. The assembly manufacturer may be a different organisation to the original manufacturer. Where the

assembly manufacturer introduces changes to the assembly configuration tested by the original manufacturer, he is deemed to be the original manufacturer in respect of these changes and he has to carry out the design verification. Design verification replaces TTA and PTTA categories Design verification replaces type tests so the discrimination between type-tested assemblies and partially type-tested assemblies is eliminated. Three different but equivalent types of verification of requirements are introduced: Ve r i f i c a t i o n b y t e s t i n g : Te s t conducted on a sample of an assembly or on parts of assemblies to verify that the design meets the appropriate requirements. This method is equivalent to the currently implemented type tests. Ve r i f i c a t i o n b y c a l c u l a t i o n / measurement: Calculations applied to a sample of an assembly or to parts of assemblies to show that the design meets the appropriate requirements. Verification by application of design rules: Specified rule to verify the design of an assembly. The selection of the appropriate verification method must be done according to Annex D which explains the available verification options for each characteristic to be verified, as shown in Table 2.
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Temperature rise: Temperature rise requirements are explained more clearly and are adapted to the state of the art. One of the following methods is allowed for verification: Testing with current. Derivation (from a tested design) of ratings for similar variants. Calculation. RDF: The rated diversity factor (RDF) is covered in more detail. In practice, it is assumed that multiple functional units are not fully loaded simultaneously. Labels: Labels must be subjected to testing to verify their legibility. The following information is required on the label: Assembly manufacturers name. Identification number. Date of manufacture . IEC 61439-X (part X must be specified). Grey areas: A number of grey areas have been clarified: Neutral conductors will have a current rating equal to 50% of the corresponding phases if not specified otherwise.

Characteristics to be veried 10.2 10.3 10.4 10.5.2 10.5.3 10.6 10.7 10.8 10.9.2 10.9.3 10.10 10.11 10.12 10.13 Strength of material and parts Degree of protection of enclosures Clearances and creepage distances Effective continuity between parts and PE Effectiveness of the assembly for external faults Incorporating of apparatus Internal electrical circuits and connections Terminals for external conductors Power frequency withstand voltage Impulse withstand voltage Temperature rise limits Short-circuit withstand strength EMC Mechanical operation

Verication by testing Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes Yes Yes

Verication options available Verication by calculation Verication by design rules No No No Yes Yes Yes No No Yes Yes No Yes No Yes No Yes No No No Yes Yes Yes Yes Yes No Yes No No

Table 2: Characeristics to be verified.

Agreements between customer and manufacturer have been more detailed, extended and listed in annex C. It is mandatory to specify the rated current of the assembly. A technical report IEC 61439-0: Guide for specifying assemblies is under development for a better understanding of the new standard. Questions regarding the internal form of separation have been clarified (e.g. a moulded case circuit breakers casing provides separation from other functional units). Responsibilities With regard to responsibilities, the general and obvious rule is that the manufacturer of the assembly is responsible for it. One could also say the original manufacturer usually makes design verifications and assumes responsibility for the proper functionality of prototype assemblies. He provides a portfolio of verified assemblies and each player in the electrical market who becomes the assembly manufacturer can manufacture a design-verified assembly by following the instructions supplied in the original manufacturers instruction manual or catalogue; the assembly manufacturer assumes responsibility for the assembly, labels it and declares that the assembly complies with the relevant standards. In practice, he has two options: He decides to manufacture the assembly according to the rules of the original manufacturer. In this case, the assembly manufacturer must perform only the second stage verification, namely routine verification. He decides not to manufacture the assembly according to the rules of

the original manufacturer. In this case, the manufacturer incorporates his own arrangements so that he is deemed to be the original manufacturer. He must then carry out both the first and the second stage verification: design verification and routine verification. Hypothetical examples An original manufacturer assembles a complete assembly and sells it to a panel builder. The panel builder is only the assembly manufacturer if he installs the assembly as is. The panel builder is the assembly manufacturer and becomes the original manufacturer if he makes some modifications to the assembly. A panel builder assembles a complete assembly according to the rules of the original manufacturer. The panel builder is the assembly manufacturer and is responsible for the assembly provided that the electrical installer installs the assembly without making any alterations. A panel builder assembles a complete assembly (according to the rules of the original manufacturer) which has been assembled partially by an external supplier. The panel builder is the assembly manufacturer and is responsible for the assembly. FAQ Until what point is it possible to manufacture and to install assemblies in accordance with IEC 60439? The validity of the two standards will overlap until 2014, and prior to this date assemblies can be manufactured according to IEC 61439 or IEC 60439. If tests on the assembly have been conducted in accordance with
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IEC 60439, is it necessary to repeat them in accordance with the new IEC 61439? No, if the conducted test results fulfill the requirements of the new IEC 61439 it is not necessary to repeat them. It is necessary to test only the additional verification that has been introduced by the new standard. Is it possible to manufacture an assembly in accordance with the new IEC 61439, with enclosures, busbars, circuit breakers etc. from different manufacturers? Yes, it is possible but it is not easy and it is expensive. The panel builder who decides to mix different elements from different manufacturers is not only the assembly manufacturer, but becomes the original manufacturer and has to perform both first and second stage verification: design verification and routine verification. The routine verification is similar to the present routine test and is relatively straightforward. The design verification, however, includes some characteristics which are easily verified, and others which can only be verified through laboratory testing. What is the rated diversity factor (RDF)? The RDF is the per unit value of the rated current, to which outgoing circuits of an assembly can be loaded continuously and simultaneously (the mutual thermal influences must be taken into account). It can be declared for groups of circuits or for the whole assembly. The RDF has to be assigned by the assembly manufacturer (if not specified it is assumed to be equal to 1). In practice, it is recognised that not all circuits in an assembly operate at rated current continuously and this allows efficient use of materials and resources.

Is it possible to substitute a device within an assembly? What about temperature rise and short circuit strength? The new IEC 61439 clearly defines a device substitution in respect of temperature rise and short circuit strength. In terms of temperature rise, it is possible to substitute a device without repeating design verification, provided that the new device from the same or another series has identical or better values regarding power loss and terminal temperature rise compared with those of the original device, as tested in accordance with the product standard. In terms of short circuit, it is possible to substitute a device without repeating the design verification, provided that the new device is identical. If different, it must from the same manufacturer who has to certify that it is equivalent or better with regard to all relevant short circuit characteristics. Is the verification of the short circuit withstand strength required for all circuits of an assembly?

No, it is not required for: Assemblies with rated short-time withstand current or rated conditional short circuit current not exceeding 10 kA rms. Assemblies protected by currentlimiting devices with cut-off current not exceeding 17 kA at the maximum permitted prospective short-circuit current at the terminals of the incoming circuit of the assembly. Auxillary circuits of assemblies intended to be connected to transformers whose rated power does not exceed 10 kVA for rated secondary voltages of no less than 110 V, or 1,6 kVA for a rated secondary voltage less than 110 V, and whose short circuit impedance is not less than 4%. All other circuits must be verified. Does the verification of temperature rise remain unchanged? Temperature rise requirements are explained in further detail. Three different methods are now allowed for verification (the original manufacturer

is responsible for choosing the suitable verification methods): Testing with current: Three different test methods are permitted and the original manufacturer must determine the best method. When a number of variants of an assembly must be verified, the most onerous configuration has to be tested and the ratings of the less onerous (and similar) variants can be derived without testing. Derivation: (from a tested design) of ratings for similar variants. The standard defines a series of subclauses that help define how nontested variants can be verified by derivation from similar arrangements verified by test. Calculation: Two calculation methods are allowed: single compartment assembly with rated current not exceeding 630 A (done by calculating the total power loss of the assembly if certain conditions are fulfilled), and multiple compartment assembly with rated current not exceeding 1600 A (done by calculation in accordance with the method of IEC 60890 if certain conditions are fulfilled). Conclusion The new standard IEC 61439 introduces important modifications in comparison with the current standard IEC 60439 on low voltage switchgear and controlgear assemblies. The structure of the new standard is clearer with a general part and product-specific parts. New definitions have been written (e.g. original manufacturer and assembly manufacturer ). New compulsory characteristics must be specified (e.g. rated current of the assembly). A new design verified assembly concept has been specified. This new concept completely discards the categories TTA and PTTA, and the compliance of an assembly can now not only be verified by means of tests, but also with alternative methods: calculation/measurement and design rules. The new standard is more precise, eradicating the grey areas contained in the previous standard. The responsibilities for an assembly are clearly defined, making the job of each actor on the electrical market easier nowadays. Contact Kovilan Chinnathambi, ABB South Africa, Tel 010 202-5097, kovilan.Chinnathambi@za.abb.com

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