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04 January 2015 04:24 pm
Zoro Posts: 300 Joined: 31 July 2011	The reason for the change to Metal clad is because the existing Plastic CU's do not meet the current BS/EN standard for 650C Glow wire tests, other than the Schneider boards. Independent laboratory tested results. "A recent series of ignition tests was undertaken on five brands of plastic consumer units. The tests were initiated by the London Fire Brigade and undertaken with the collaboration of Bureau Veritas Solutions and the Electrical Safety Council. Initial tests identified that three of the five plastic enclosures did not use a flame retardant in the plastic. The other two brands used enclosures with a flame retardant incorporated in the plastic. The first series of tests were confined to replicating the hot wire material test as specified in BS/EN 60947-1: 2007 + A1:2011. Criticism could be raised by the manufactures of consumer units as BS/EN 60947 is not a 'product test'. However, the test successfully identified the ease in which the plastics used in the construction of the enclosures were ignited. A pre-conditioned hot wire is wrapped around a plastic sample and the wire is then energised with prescriptive electrical limits for up to 30 seconds. In these tests a maximum wire temperature of 550°C was measured. The results of the hot wire tests were that with the exception of one sample of plastic that had a flame retardant (Schneider), all of the plastic samples ignited irrespective of whether they did or did not have a flame retardant incorporated in the plastic. The shortest time to flaming ignition was 11 seconds for a plastic sample without a flame retardant and 16 seconds for a plastic sample with a flame retardant. All five plastic consumer unit enclosures were subjected to a needle flame test in accordance with the EN 60695- 11-5:2005 standard. The needle flame was introduced into the consumer unit via a small opening to enable access to the main neutral connection at the neutral connection bar. One of the consumer units with a flame retardant did not ignite and the flame was applied at four additional areas, again without ignition. The second consumer unit with a flame retardant ignited and once the needle flame was removed, the flame self-extinguished within eight seconds. The remaining three consumer unit ignition tests resulted in fires that spread from the initial needle flame to involve the entire plastic enclosure. The shortest time from needle flame application to the ignition of the plastic was eight seconds. Two of the ignition tests had to be halted after four minutes as the smoke being produced by the fire began to overwhelm the dedicated extraction system of the test facility (figure 3). Plastic Consumer Units in the UK have to be constructed in accordance with BS EN 60439 (replaced in 2011 by BS EN 61438). The plastic enclosures have to withstand 660°C glow wire product tests. The opinion of the author is that this test is not sufficient to ensure the safety of the occupiers in properties where plastic consumer units are installed. The data previously detailing fires that have originated within consumer units in the London area, resulting from various types of defective electrical connections, shows an increase in these life threatening fires. The plastics used in the construction of consumer unit enclosures should therefore be more resistant to ignition from an internal defective electrical connection. In addition, the product should be constructed to ensure that any localised heating within the consumer unit should be contained within the product." It should be a Recall by the manufactures, a change to BS7671 AMD3 has been used to avoid this, which is why there is so much controversy. "So keep installing them till 2016 to use up the stock." Specifications for equipment should be to the BS/EN standard, not through the back door of BS7671, for commercial reasons. . Edited: 04 January 2015 at 04:41 pm by Zoro
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