WINDING OF ALTERNATING-CURRENT ARMATURES 319 



The winding is a 20-pole, 3-phase, half-coiled, quadruple-coil, 

 spiral winding in 2 ranges. For a half-coiled winding the number 



20 



of coils per phase will be = 10 per phase, or 10 x 3 = 30 coils in 



2 



30 

 all i.e. = 15 coils in each range. 



FIG. 390. Winding Armature with Strip on Edge (Mavor & Coulsoii). 



Table XIV.. p. 203, gives us 4 slots per pole per phase, and 

 hence the total number of slots is 4x3x20 = 240 slots. 



For example of finished 3-range windings we may refer back 

 to Figs. 253 and 257 in Chap. IX. 



Form-wound Spiral Coils. As stated at the beginning of 'this 

 chapter, form-wound coils are not desirable for coils other than 

 single coil or double coil at most, owing to the number of formers 

 required. 



Where the conductors are wire or fairly small strip (with 



