 Table 1 - Starting Torque /Current with 3 Reduced Voltage taps 
Manufactures offer their reduced voltage autotransformer in two configurations, with a 2 coil construction or with a 3 coil construction, figures 2 and 3.Each apparatus has reduced voltage taps at 50%, 65% and 80% based upon National Electrical Manufacturers Association recommendations.The phase coils are traditional wound in a single coil assembly with the 0 to 50% winding section buried below the 50% to 100% windings in a single thermal mass as shown in figures 2 and 3

Figure 4 shows an improved 1000 kW 11,000 Volt motor starter autotransformer with 

Table 2 - Starting Torque /Current with 9 Reduced Voltage Connections

The thermal dissipation of the first starting stage is maximised by being a physically separated winding from the windings of the second starting step to full line voltage.