First of all there should be a consultant who has prepared specifications,drawings,BOQ etc
There should be a contract and programme of work approved by consultant
Shop drawings should be approved.
Check material according to specifications and BOQ,submit samples for approval
Start installation in the presence of consultant
Then lay cables and connect as per drawing
If you notice any discrepancies in the drawing report to consultant and get amended
Let consultant do a visual inspection and clear any remarks
Afterwards test(primary/secondary) injection for relays,oil,CB,battery,alarms,earth etc in the presence of consultant
After test results were approved by consultant you may energise section by section