This is WorkSafe's interpretation:
"A PCBU means a Person Conducting a Business or Undertaking.
It's a broad concept used throughout HSWA to describe all types of modern working arrangements which we commonly refer to as businesses.
Most New Zealand businesses, whether large corporates, sole traders, or self-employed, are classed as PCBUs.
The difference between a business and an undertaking is:
businesses are usually conducted with a view to making a profit and have a degree of organisation, system and continuity.
undertakings will have elements of organisation, systems, and possible continuity, but are usually not profit-making or commercial in nature."
So, while PCBU is stated in legislation as a ‘Person Conducting a Business or Undertaking’ (HSWA 17(1)(a)), the interpretation is that businesses are PCBUs (see
Legalvision) regardless of whether sole traders, partnerships or limited liability companies.
A PCBU's primary duty is to ensure so far as reasonably practicable the health and safety of its workers while at work for the PCBU and any workers whose activities in carrying out work are influenced or directed by the PCBU while carrying out the work (e.g. temp workers) - see
Brookfields
Responsibility for ensuring the PCBU meets its duties, is the role of officers in the business (HSWA 44(1)).
WorkSafe's interpretation is
"An officer holds a specific role in an organisation that allows them to exercise significant influence over the management of the business or undertaking. Officers have a due diligence duty under the Health and Safety at Work Act 2015 (HSWA)." See
Officers' due diligence
So in your example:
"Take Fred and Bill the builders who build houses. Fred and Bill are the bosses but the company is owned by Bert who has retired? There is Simon who is the supervisor."
The business owned by Bert that is run by Bill and Fred and employs Simon is a PCBU
If Fred and Bill have significant influence over how the business is run then they are officers and have duties
If Bert has significant influence over how the business is run then he is an officer and has duties
If Bert does not have significant influence over how the business is run then he is not an officer and does not have duties.
Same applies to Simon.