During control panel installation why it is necessary to be controlled with a single wire control wire ?

Identify and label each wire before pulling through conduit into control panel and junction box. Pull pump power cables and control switch cables through connectors into junction box. Make wire splice connections at junction box.

 If control switch cables are not wired and mounted in the correct order, the pump system will not function properly

its a control panel, so we need the control signals only, the control signals are in Extra Low Voltage, so depends up on the resistance and signal transmission we used single wire and control wires

câbles alimentation électrique

During control panel installation it is necessary to be controlled with a single wire control wire because we need just phase to illuminate LED 

due to more accurate control and simplicity ans well as security