This part of ISO 1680 specifies, in accordance with ISO 2204, an engineering method (grade 2) for measuring the sound pressure levels on a rectangular parallelepiped surface enveloping the machine and for calculating the sound power level produced by the machine. It outlines the procedures which may be used to evaluate the test environment and specifies the characteristics of suitable measuring instruments. A method is given for determining the A-weighted sound power level and, if required, octave or one-third octave band sound power levels of the machine from the mean of the sound pressure levels measured on the rectangular parallelepiped surface.This part of ISO 1680 applies to the measurement of airborne noise from rotating electrical machines, such as motors and generators (d.c. and a.c. machines) without any limitation on the output or voltage, when fitted with their normal auxiliaries. It applies to rotating electrical machines with any linear dimension (length, width or height) not exceeding 15 m.This part of ISO 1680 applies to measurements carried out in environmental conditions that meet the criteria given in clause 4 and annex A (environmental correction K 2 dB, correction for background noise 1 dB). If these criteria are not met, standard deviations of the test results may be greater than those given in table 1, i.e. the engineering grade of accuracy may not be achieved. The method given in ISO 1680/2 shall then be used, which will result in A-weighted sound power levels of lower accuracy. In this case, no reference shall be made to this part of ISO 1680.