Hi,
To answer your question will use the JBC as the basis.
WHAT THE TERMS MEAN AND THE DIFFERENCES
Domestic subcontractors are not distinguished from the main contractor in conditions of contract as they are assumed to be part of the main contractor.For the nominated sub contractors there is a difference because of the client's right of choosing the subcontractor. This arises where
i) There is a prime cost sum in the contract bills (BQ) and this often refers to the works in breif
ii) Where an architect issues instructions regarding expenditure of provisional sums.
The contractor prices for attendance requiring preparation and arrangement for work by the contractor for the sub contractor. The main difference is in the appointment, the contractors liability remains the same.
ADVANTAGES AND DISADVANTAGES
1. With the nominated sub contractor the owner is given the authority to select the sub contractor at any time, even long after the main contract has been entered to.
2. In such contracts there is a possibility of cost claims by the MC in delay of nominated contractors but this rarely happens because the contact is between the nominated sub contractor and the MC.
3. With the nominated sub contractor the client is able to make comparison among the subcontractor and choose the most suitable one to take over the specialist work.
Will comment on the rest later.