Technology

Introduction to isolation and switching

This article from ELECSA provides a brief overview of isolation and switching how the terms are used in BS 7671. The term ‘isolation and switching’, as used in BS 7671, embraces four distinct concepts, each with its own particular requirements for safety. The four concepts are: isolation, switching off for mechanical maintenance, emergency switching, and functional switching. This article will only consider isolation. Summary of the four safety concepts Switching off…

Identifying electrical accessories

In this video, GSH Electrical and Tresham College introduce basic electrical accessories. This video has been made as a student aid for identifying basic electrical accessories. We look at 1-way, 2-way and intermediate switches, lighting points and socket outlets. It’s important in the early stages of training to be able to recognise and name these items. All products are donated by Scolmore

How do I determine an extraneous conductive part?

This article provides some simple guidance on how to identify extraneous conductive parts to help you avoid the unnecessary installation of protective bonding conductors. It should be appreciated that exposed metallic parts not forming part of the electrical installation are not always extraneous conductive parts as defined in Part 2 of BS 7671. Therefore, as explained in this article, to avoid the unnecessary installation of protective bonding conductors, it is important…

An introduction to earthing and bonding

Earthing and bonding are two very different, but often confused, methods of preventing electric shock. The principal of earthing is to limit the duration of touch voltages if you were to make contact with an exposed conductive part. The earth creates a safe route for the current to flow instead of causing electric shock. The purpose of bonding is to reduce the risk of electric shock if you find yourself…

An overview of cable management systems

There are a wide variety of containment systems available to organise and store cables within an installation. They tend not to be used exclusively for a particular type of wiring system, and the containment system chosen is often as much decided by the budget and practical considerations of the building it is being installed in as the cabling type itself. Fixings in cable management With such a range of cable…

How do you select the right MCB or RCBO?

Technology continues to evolve in the field of low-voltage power distribution and protection. 30 years ago the installer was typically faced with the decision on what size fuse wire to use. Now they must consider which MCB or RCBO to install, with even more choice than ever on what levels of protection against the effects of electrical fault to afford. Released in 2018, BS 7671: Requirements for Electrical Installations (IET…

How does an MCB work?

This excerpt from ABB introduces the technology inside and miniature circuit breaker (MCB). What does an MCB do? The short answer: it protects wires from overloads and short-circuits. When we look on the inside of an MCB we can see how that actually works. For overload protection the temperature of a bimetal, through which the current passes (yellow area), is decisive. If the nominal current—the current the circuit breaker is…