194 



TREATISE ON ALTERNATING CURRENTS. 



mains we multiply the reading by 2. If it be connected from one 

 main to the centre of the system then the multiplying factor is 3. 

 An important case is when the volt coil of the meter forms 

 one of the arms of a star- box. If the three arms are of equal 



FIG. 82. 



resistance, the multiplying factor is 3. If, however, as is often 

 the case in practice, the resistance of the volt coil be different from 

 that of the other two arms, then it is known that the multiplying 



factor is 2 -f -^ where E is the resistance of the volt coil and r 

 that of either of the other arms of the box. 



FIG. 83. 



