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When found the service fuses and their panel were lying amongst the charred debris on the floor of the first floor due to the collapse of the wooden wall on which they were mounted. In order to determine the manner in which the service fuses were blown tests were carried out under controlled conditions with the object of reproducing similar physical effects as those shown by the service fuses. Physical Effects on Fuse Links Blown in Various Ways Tests were carried out on a set of ten fuse links similar to the heaviest of those used in the service fuses at Ballantynes at the time of the fire. Each link consisted of twentytwo strands of 0-029 in. tinned copper twisted tightly together and having an overall length of 8 in. The ends of these links were divided into groups of 5, 5, 5, and 7 strands, which were secured to heavy brass blocks by means of four clamping screws. The link itself was enclosed in an asbestos tube of \ in. internal and f in. external diameter. The recovery voltage throughout all these tests was approximately 12 volts, which permitted a true indication of the physical conditions of the fuse links at instant of Wowing as no destructive arc was formed by a high recovery voltage in the order of 230 or possibly 400 volts as would be found in normal service. At 300 amps the central portion of the fuse link maintained a temperature approaching melting-point (cherry red), but did not blow after fifteen minutes. The lowest fusing current was found to be 325 amps with a fusing-time of six minutes twenty seconds, and the interstrand welding extended over a length of approximately \ in. With an increase in fusing current the time decreased and the interstrand welding increased, until at 1,200 amps the time was only five seconds and the length of weld was approximately 5 in. (see Fig. 111, page 102, for time-current curve). With reference to length of interstrand welding this measurement is that between extremities of interstrand welding with the original ends of the fuse links 8 in. apart. From test samples of blown fuse links submitted herewith it is seen that at low fusing currents the length of the link raised to melting-point is very short, while at high fusing currents (1,200 amps or over) the length that has been raised to meltingpoint is practically the full length of the link. From the above results curves (a) and (b) Fig. I, are typical temperature gradients for low and high fusing currents respectively, while curve (c) is considered to be the temperature gradient for a current below minimum fusing value.

Fig I. —Length of Fuse link.

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