The International Electrical Standards commonly referred to as the IEC Standards, have always served as a guideline that helps industry stakeholders to produce products and assemble systems that are in line with global standards.
The IEC 61439 Standard applies specifically to Low Voltage Switchboards and has superseded the IEC 60439 that was previously applicable.
The IEC 61439 is now the governing standard for Low Voltage Switchgear and Control gear assemblies for enclosure systems below 1000V AC (at frequencies less than or equal to 1000Hz) or 1500V DC.
IEC 61439 makes elaborate improvements over its predecessor, improvements that significantly enhance the quality and safety aspects of LV Switchgear and Control gear. It also removes many of the misunderstandings and short comings of IEC 60439 and provides clear guidelines to all the stakeholders including Specifiers, Manufacturers, Assemblers and ultimately Clients.
Within the general rules section IEC 61439-1 and the specific rules section IEC 61439-2, the new standard eliminates the earlier definitions of TTA (Type Tested Assemblies) or PTTA (partially Type Tested Assemblies) with an all encompassing Design Verification concept.
What is Design Verification?
Design Verification involves the establishment of conformity of the Assembly design to the IEC requirements by three equivalent / alternative methods which are Testing, Calculation / Measurement or the application of design rules.
By applying one of the three methods as allowed by the new standard, compliance for assemblies can be established without the ambivalence that was previously prevalent with PTTA assemblies as defined in IEC 60439.
5 Key Changes in the Standards
1- The PTTA concept has been discarded
IEC 61439 eliminates the need for using PTTA assemblies, allowing manufacturers three equivalent methods to prove compliance to the new standard. Hence TTA / PTTA concept is discarded.
2- Clarity in the roles performed by an OEM(Original Equipment Manufacturer) and an Assembler
IEC 61439 clarifies the roles of an OEM and Assembler by introducing new definitions.
The OEM refers to the manufacturer of completely tested and certified products and systems. For example, the proprietary Dorman Smith “MODIS Ultra System “– tested and certified with Dorman Smith components.
An Assembly Manufacturer refers to a firm procuring components , for example, from Dorman Smith and assembling the complete Low Voltage systems.
If you would like to know more about Choosing an Assembler, read more
As an OEM Dorman Smith is responsible for the design, assembly and design verification of the complete LV system, in this case, the MODIS ULTRA Form 4 LV switchboard system.
The Assembly Manufacturer may or may not be a different company but buys the system from the OEM and takes full responsiblity for the final assembly.
This is a significant change and clears any confusion regarding the responsibilities of the owner of the design (OEM) and the assembler (assembly manufacturer). If the Assembly Manufacturer makes changes to the design of the OEM they then become the OEM and have to design verify the system to prove compliance.
3- Additional Testing Requirements
New verification requirements have been introduced with respect to Empty Enclosures, such as corrosion resistance, impulse withstand, lifting, marking etc which did not feature in IEC 60439 and are part of IEC 62208 for Empty Enclosures.
4- Clarification in Temperature Rise Test Requirements
Temperature rise test requirements have been well defined and ambiguities have been removed in the new standard. Testing can be done “with current”, “derivation (comparison with similar variants)” or by “calculation”. This eliminates guesswork and misrepresentation.
Rated Diversity Factor is now defined in detail.
While it is understood that all the devices in a switchboard may not be fully loaded at once, it is possible for one or more devices in the assembly to be fully loaded. The standard takes this into account by requiring testing of individual circuits to their rated current, thus ensuring that the total diversity factor does not preclude a specific circuit from carrying its actual rated current.
5- Routine Verification is Explained
Routine Verification of each assembly is now defined and replaces Routine Testing. Routine Verification is to be performed by the Assembly Manufacturer to establish compliance to the tested / design verified designs.
The standard also clarifies the substitution of devices (for example from another manufacturer) in a design verified system. Unless the Assembly Manufacturer can prove that the devices are equal to or better than the devices with which design verification has been established, then swapping of devices is to be avoided.
The standard establishes the criteria with respect to Temperature Rise and Short Circuit Performance for device substitution by relating the Power Loss and Terminal Temperature rise characteristics and the Short Circuit Performance Characteristics of both devices.
If this cannot be proven, then the Assembler becomes an OEM (due to device substitution) and has to then perform Design Verification on the system to establish compliance and Routine Verification as well and carries the responsibility for the final assembly.