Oh lord, why can you never provide something that actually HELPS the topic. It's always a nit pick, never anything constructive...
Indeed why, why, why???
There is a single sign certificate that indeed includes the design, install and test when a sole person has done it all.. Anyone who has experience in the real world (or has a copy of BS7671) will know that there is also a separate installation cert where different (competent) persons are responsible for and certify the separate activities.
If an electrician and his assistant install a new circuit, the assistant is not required to sign the documentation.
The assistant can quite legitimately be the customer as long as long as they follow the electricians instruction.
There appears to be spaces for
A designer to sign the form as "designer"
An installer to sign the form as "installer"
An inspector to sign the form as "inspector"
Three separate people,
Or am I getting it wrong
My interpretation of this (which I'm extremely happy to be corrected) is the different boxes are to be used when different trades complete the sections, I'm thinking more in terms of 'commercial' jobs where the architect does the initial building design, then different specialists (such as ME company) do thier design and the project goes out to tender, then various companies tender for parts of the project, then in this case an electrical company is appointed and parts are sub tendered and sub sub tendered to the lowliest person.
In my case Sunray builds and installs a control panel as a sub to 'Controls are us'.
'Controls are us' may or may not install the cable management for the controls system. They sub to 'ABC environment services' who install the air handling units and ducts.
'ABC environment services' sub to 'Laing ME' who get the contract for all of the mechanical/electrical services such as ventilation, heating, plumbing, drainage, etc
'Laing ME' sub to 'Laing' who get the whole contract for the project. and may very possibly put all of the inspecting out to 'We do Quality Control Ltd'
I don't think (which again I'll stress I' extremely happy to be corrected) the 3 boxes are intended for use when 'Eric the electrician' adds a shed supply but, under supervision (However loose that is), the house holder digs the trench and lays the cable in to save money.