8 steps to begin basic circuit design

How do we begin to design?

What do we need to know? Clearly, plunging into calculations of cable size is of little value unless the type of cable and its method of installation is known. This, in turn, will depend on the installation’s environment.
At the same time, we would need to know whether the supply was single or three-phase, what the earthing arrangements were and so on.

Having ascertained all the necessary details, we can decide on an installation method, the type of cable and how we will protect against electric shock and overcurrents. We would now be ready to begin the calculation part of the design procedure.
Basically, there are eight stages in such a procedure. These are the same whatever the type of installation, be it a cooker circuit or a steel wire armoured (SWA) cable feeding a remote garage.

8 steps

Here then are the 8 steps to begin basic circuit design in a simplified form:

1. Determine the design current I_b
2. Select the rating of the protection I_n.
3. Select the relevant rating factors (CFs).
4. Divide In by the relevant CFs to give tabulated cable current carrying capacity I_t.
5. Choose a cable size to suit I_t.
6. Check the voltage drop (Use MS Excel Spreadsheet to calculate).
7. Check for shock risk constraints.
8. Check for thermal constraints.