Control Panel Wiring

[oreoreo]

I'm college student currently studying industrial automation so this question might seem basic. 

The text in the first picture (screenshot(590)) states that the number of wires needed for n machines are 3n, as shown in figure 3.14d (second picture, screenshot(591)). However, if the thermal overload relays are placed between relays Ci and Neutral, this number can be reduced to 2n + 1, as stated in the highlighted text. 

I'm having trouble to picture said wiring with 2n + 1 wires. Can anyone help? 

[박주영]

Perhaps 3n is the power line.
I think you need to understand the power line and the control line. For thermal overload relays, you can connect 3n(RST) wire or connect 2n(RT) wire.