Electrical systems design can range from the extension of an installation in a small flat to a multi-million pound new installation on a green field site with a load of many megawatts.
Some designs are well within the scope of an electrician others require the services of specialist design engineers.
The diversity of the subject is such that it has to be broken down into sub-systems, this part of the web site is divided into the major sub-systems, with each sub-system being broken down further and, hopefully, examples that are useful to readers given.
Large electrical installations will have a number of different sub-systems, it is for the system designer to design the sub-systems and to integrate the sub-systems into the overall system.
It is essential that the system designer understands project management, project planning and financial management so that sub-systems become sub-projects.
Each sub-systems should, therefore, form a sub-project and conversely each sub-project should be a sub-system; each having it’s own drawings, specifications and contract documents, obviously, it will also have it’s own management, planning and financial control.
By creating clearly identifiable sub-projects it makes managing the sub-systems, the keeping of proper financial control and project management simpler.
An example of a sub-system is standby generation. A standby generating system will normally be a separate sub-contract to the main contract or a standalone contract. The system will consist of one or more generators complete with their fuel storage, fuel supply, starting and control systems and their output switchboard(s). The interface with other electrical systems will be minimal and thus manageable.
A major sub-system will be the electrical distribution system which is defined as the taking of electricity from a point or points of supply and conveying it to the point or to the points of utilisation. Within a building or establishment we can divide the distribution into three; the primary, secondary and final. Each will form a sub-sub-system which will each be a separate sub-project with it’s own finance and planning.
The primary distribution is that part of the distribution system from the electricity supplier to the first level of LV distribution boards or switchboards.
The secondary distribution is that part of the distribution system from the first level of LV distribution boards or switchboards to the final distribution boards.
Final distribution is that part of the distribution system from the final distribution system distribution boards to the points of utilisation.
Not every building or establishment will contain secondary distribution all will contain primary and final. For example a house has primary distribution from the meter to the distribution board and final distribution from the distribution board to the sockets, lighting points and fixed points of utilisation.
An example of a building with all three levels of distribution would be a data centre. The building will require two diverse MV supplies from the PES (Public Electricity Supplier) with an automatic change over system between them, each supply would feed duplicate switchboards which in turn supply the main LV switchboards via transformers. Each transformer being rated for the entire building load. A generating system would supply each main LV switchboard and the critical loads. Secondary distribution would take power from the main LV switchboards to the final distribution boards on each floor and in each area. The final distribution will be from the final distribution board to the sockets, lighting points and fixed points of utilisation.