I think we all do well to assimilate all the rules & regs ..AND...actually find time to do a job .
Also thinking , if you are an employed sparks its often the case that the firm/boss/supervisor/foreman would say :-
Go to this place .
Pick up pre-ordered list of gear from the wholesalers on the way.
Install the cable from the board to the new machine .
I'll come out in two days , test & commission it .
For this you are paid the appropriate rate .
As self employed you have visited site , checked the requirements of the machine , measured the run, done some calcs, checked the existing board loading etc. rfeturned to office , worked out a quote , typed it up , posted/ emailed it in , won it , loaded the van with ladders etc, collected the gear , installed it , tested it , commisioned it , back to office , raised an invoice , typed it up , posted it , waited 60 days for the cheque to arrive , go to bank , pay it in , feed family.
In other words , make sure you are charging the correct rate for what you do .