Abstract :
The efficiency of the end connections, which was discussed by a Committee of the British Engineering Standards Association when considering the standardization of shunt ends and switchboard connectors, has been investigated. The results show that with brass lugs the contact resistance is considerably higher than with copper, and also that with brass ends the pressure-drop across the two joints is of the order of 20 mV as compared with 75 mV across the shunt itself. With copper ends the voltage-drop is only 3 mV. The temperature-rise of the resistance elements of shunts carrying overloads was investigated. The amount of overload which a shunt will carry during short periods before a given temperature excess is reached depends almost entirely on the heat capacity of the metal of which the shunt is composed, the effects of radiation and convection under these circumstances being negligible by comparison. Formulae for the evaluation of short-period overloads were deduced from the dimensions of typical shunts for a given value of the temperature excess, and were checked by results obtained from actual overload tests.
