Electrical equipment engineering cost, how the wire is wired?

From the distribution box out of the general laying along the canopy lighting mains power, first to the lights, each light set back to the box, and then from the return box to the switch to lay 2 wires, usually like this.

From the distribution box out to the switch first, and then to the lights, adapting to the switch is close to the distribution box (in the switch to set the return box), the lights from the distribution box far away from this situation. In short, low-voltage wiring needs to be applied flexibly. Zero line in the cost of electrical equipment does not need to be excluded from the calculation. Low-voltage wiring detailed reference building electrician books.