General

Looped Lighting Circuits – Electrical Installation 101. The most common method is the ‘loop in’ system. This is where cables loop in and out of each lighting point, which is usually a ceiling rose. The wiring may be a Twin and Earth PVC/PVC cable consisting of a Line, Neutral and CPC (in), a Line, Neutral … Read more

Automatic disconnection of supply (ADS) is the most widely used method for achieving protection against electric shock in an installation. It works by limiting the size and duration of any voltages between exposed-conductive parts / extraneous-conductive parts or Earth. This is achieved through a combination of factors that must be in place. Basic Protection: Provided … Read more

Voltage Drop Think of voltage drop as similar to a loss in pressure along a water pipe over a long distance. So just like with water in a pipe a conductor will lose ‘x’ amount of pressure measured in millivolts ‘mV’ for every Amp ‘design current’ that flows along it for each meter. This is … Read more

The purpose of performing a cable calculation is to ensure that a cable is not overloaded. This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. So, here’s how that’s done… Firstly how much current is your appliance going to use? … Read more

Just a short one this week… Special Locations are locations or installations where there is an increased risk of receiving an electric shock. For this reason and according to BS7671 Part 7 Section 701 any location containing a bath or shower is deemed a ‘special location’. So that’s the whole of the bathroom! 701.32.2 to … Read more

This is more of an electrical general knowledge question rather than a Wiring Regulations one but they do pop up in the City & Guilds exam every so often. “A twin and CPC, PVC cable has a 2.5 mm line conductor with a resistance of 0.46 ohms and 2.5 mm neutral conductor with a resistance … Read more

Appendix 15 in BS7671 is probably the most useful practical description in the whole book. If you want to know what you can do and what goes where it’s all here. Ring Socket Circuits… Spread your sockets around evenly to avoid overloading any part of the ring. Don’t put immersion heaters, storage heaters on the … Read more

The maximum disconnection times for a TT system is 0.2 seconds for final circuits up to and including 32A (Table 41.1) and for distribution circuits or circuits greater than 32A it’s 1 second (411.3.2.4). The problem is that with TT systems the external loop impedance value (Ze) will be too high to achieve these 0.2 … Read more

Prospective Fault Current (Ipf) is the general term used for the highest amount of current that will flow under fault conditions. On a single phase installation fault conditions can either be Prospective Earth Fault Current (PEFC) Line to Earth or Prospective Short Circuit Current (PSSC) Line to Neutral. Whichever one is the highest would be … Read more

How it works Our 17th Edition online training course is real home training and support and based on a traditional 3 – 4 day classroom course. Specially designed to prepare and assist you in passing your City & Guilds 2382-10 exam. Let’s go through the book together A full cover to cover review (Part 1 to … Read more