POWER SUPPLIES & GENERATORS
are taken into account. In the past only the heat produced due to conductor resistance was considered.
In order to optimise testing time, the standard allows derivation of the rating of similar variants without testing, assuming the ratings of ‘critical variants’ have been established by test. For example, if the acceptability of a 15KW DOL Starter circuit is verified by test, subject to rules defined in the standard, the rating of a circuit comprising of a 7.5 KW DOL starter using the same size compartment with components of lower watt losses can be derived. Normally, a special test board will be used (due to the time involved) and the results will then be compared with future assemblies to ensure compliance with the standard.
As mentioned earlier, one of the benefits of the new design verification procedure is its flexibility, under the old BS EN 60439 specification customers would demand (often unnecessarily) a Type Test certificate for each assembly particularly Incoming Air Circuit Breakers, which was very expensive and time consuming.
The new standard, however, enables manufacturers to perform a short circuit withstand test on the smallest Busbar system that will be used at the appropriate Fault Level, the Busbars may then be increased in size or thickness increasing its current rating but making it mechanically stronger. The use of the standards’ designated design check list enables the uprated system to be compared with the reference design and ensure compliance with the standard.
TEMPERATURE RISE
TESTING The new standard now contains more guidance regarding the requirements surrounding temperature-rise tests, compared with the old standard. The options are Testing, Derivation of the rated values of similar equipment and Calculation.
Using actual current when testing means that all the magnetic effects
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It also means that every time a device change is made, the Switchboard is changed and a retest may be required. However, this can be avoided by testing worst case scenarios and then ensuring the change has a beneficial effect on the temperature rise, such as: derating a Busbar or device already tested at a higher value of current, using a larger conductor to that already tested, increasing the spacing of conductors or increasing the size of a device enclosure.
When a device is enclosed in a switchboard or Motor Control Centre, some factor of de-rating usually has to be applied. By carrying out tests as described in the standard, all the other factors are taken into account at the same time and calculations are then not required.
Although some might interpret the new testing alternatives as even more unwanted hassle, in reality it allows users and specifiers to pertinently define the requirements of each application. Annex D of the BS EN 61439 standard provides a list of 13 categories or verifications required, what testing method can be used and what comparisons can be made.
DIVIDING RESPONSIBILITY The second major change
implemented by the new industry standard refers to the responsibilities of each party involved in the design, test and
implementation of low voltage switchboard assemblies. Unlike BS EN 60439, which stated the original equipment manufacturer (OEM) or the system manufacturer was solely responsible throughout the testing programme, the new standard divides the responsibilities between the OEM and the assembly manufacturer, or panel builder.
The new standard recognises that several parties may be involved between concept and delivery of a switchboard assembly. The OEM is responsible for the basic design verification. In addition, the assembly manufacturer is meant to oversee the completion of the assembly and routine testing.
“ALL THEY NEED TO DO IS MAKE SURE THEIR SUPPLIERS ARE
COMPLIANT WITH THE NEW STANDARD.”
For innovators like Boulting Technology, the new BS EN 61439 brings more freedom and flexibility when designing switchboard assemblies. For example, Boulting Technology has worked alongside ABB to test its brand new range of low voltage switchboards, which are now available in 25kA, 50kA, 80kA and 100kA up to 6300Amp for one second.
As the saying goes, with great power comes great responsibility. The BS EN 61439 standard also means that low voltage switchboard manufacturers and assembly manufacturers need to ensure they are compliant with more severe standards.
On the other hand, facilities managers and contractors can breathe easy, knowing that all they have to do in response to the new industry standard is make sure their suppliers are BS EN 61439-compliant.
Although change is never much fun, it’s what technology and industry are all about. If this wasn’t the case, we would all still be using Windows 98 or the indestructible Nokia 3310.
www.boultingtechnology.co.uk TOMORROW’S FM | 29
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