IEC 61439 is the International Electrotechnical Commission standard which covers low voltage switchgear and controlgear assemblies. The standard gives details on the requirements of these products through testing and other verification methods. It is a replacement for IEC60439. Details of the verification process are included in this article
This standard is a significant change from the previous one, one of the most surprising changes for some will be the removal of the terms ‘type tested assembly’ and ‘partially type tested assembly’, these have been replaced by ‘design verification’. With the well known seven type tests increasing to 12 design verification characteristics. A further change is that Part 1 is now ‘general rules’ with Part 2 now also required to be used for all power switchgear and controlgear assemblies. Part 6 (which is yet to be published) is to cover busbar trunking as previously covered by Part 2 of the IEC60439 series.
The twelve design verification characteristics are split down into two main areas, that of ‘construction’ and ‘performance’.
- Strength of materials and parts
This looks at the suitability of plastics and metals to prove the long term capabilities of the equipment.
- Degree of protection of enclosures
This references the same standard as before.
- Incorporation of switching devices and components
This requires the panel builder to ensure that devices are installed in line with manufacturer’s instructions.
- Terminals for external conductors
This, again, puts the onus on the panel builder to ensure that the contractor will be able to terminate his cables on to the switchboard.
- Temperature Rise
One of the biggest areas of change in the standard revolves around this area. No longer can you fit a device into a compartment and rate it at a level it would not be capable of carrying without exceeding the limits set by the standard. The standard now requires that the maximum current a circuit is capable of carrying, within the temperature limitations, is noted as its rating, irrespective of what the device manufacturers claims for the device alone.
- Short circuit withstand strength
This is principally the same set of tests as per the previous version of the standard, with a few amendments.
- Mechanical operation
This ensures the components of the system are mounted in such a way that through normal use, they will not fail or change the capabilities of the switchboard. In this case the test value is set at 200 operations.
After successfully completing all 12 design verification characteristics, the benchmark will be set for future adaptations of the design, since IEC61439 now accepts both verification by design rules and verification with a reference design, when carried out in line with the standard, are equal and equivalent to verification by test. This is another area of change that can be misinterpreted and needs full clarification by reading and understanding what options are open to users for each clause of design verification, since not all are acceptable under each clause.
Upon completion of the above, and moving into production, the standard requires routine verification be carried out by the switchboard manufacturer to ensure continued compliance to the design verified solution is met. These routine verifications must be carried out on each and every board that is manufactured and is principally a simplified subset of the 12 design verification characteristics, but this cannot be seen just as a job for the final QC department, since important areas such a device ratings, terminal sizes, swapping of components etc. needs to be fully investigated prior to any work started.
The above has concentrated on the panel builder. However consultants must also be aware of the changes that IEC61439 will bring, with some being slightly more subtle than other, but nevertheless important to what can be supplied. An excellent example of this is the slightly flawed thought we currently hold of a Form 4 assembly. Currently, most people would expect this to mean a multi compartmentalized assembly with each device being housed in its own ‘zone’. IEC60439 did not give a clear account of what an acceptable segregation method was. However clarifications within IEC61439 now confirm the outer case of a device i.e. an MCCB is acceptable to create a Form 4 assembly, without any further segregation. If the end user and consultants require a multi compartment assembly, their specifications will need to be updated to take account of this, or they could end up with a switchboard being supplied in line with the standard, but not what they actually wanted.