Use the table above as initial guidance in your choice of cable size for the standard reference method C (assuming grey 70°C twin and earth) Other factors may affect your choice of cable size when you factor in higher ambient temperatures, different installation conditions, grouping etc.

Begin by deciding on the type of circuit that is already installed – RING or RADIAL Now select the correct breaker size the table will tell you … A. The minimum size CSA of cable to use B. The maximum number and arrangement of spurs for that type of circuit. C. If an FCU is…

We are sometimes asked why the Wiring Regulations  have disconnection times  for electrical circuits. And what is the purpose of knowing how quickly a fuse or circuit breaker should disconnect an electrical circuit during a fault.  The permitted time to disconnect from the electrical source and to make safe the circuit is very much dependent…

There is sometimes a misunderstanding of just what a SELV transformer is and how a PELV transformer differs to it. So what are the differences and why does it matter to the circuit in which they are installed and most importantly, how does that impact on the safety of the users of the installation? This…

Ohm’s Law is one of the most important formulas in the electrical engineering world. It was formulated by a German Scientist, Georg Ohm, in the early 1800’s He was carrying out experiments with the new electrical cells invented by the Frenchman Voltaire. He discovered that there was a direct relationship between the voltage in a…

If you don’t know the resistor colour code then it may at first seem to be a black art, but it is actually very easy to learn and once you can use it correctly you will have a real skill for life. The method that we use at Learn Electrics is a much easier method…

Voltage Drop is a measure of how much voltage is lost in the cables between the consumer unit, the distribution board or some other reference point and the point of use. For example, we would like to know the Actual Voltage Drop in the shower cable from the house consumer unit to the shower unit,…

Many trades and occupations now ask that some of their employees are tested for colour blindness. This is particularly important in the electrical and electronic trades where many different colours are used to identify cables. Some training centres will test a new trainee’s ability to differentiate colours when they first begin their training. This can…

COLUMN NUMBERING NOTES When completing a Schedule of Test Results it is important that the correct data is entered into the correct boxes on the schedule. The Schedule of Test results will be used for comparison checks of the circuit in the future, for example at the next Periodic Inspection. It is imperative then that…

The Wiring Regulations inform us that every installation should be inspected and tested during erection and on completion before being put into service, to verify that the requirements of BS7671 have been met. In other words, we should always inspect and test our work before handing it back to the customer. We will focus here…