Sockets, Ring and Radial Circuit Arrangements

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

Maximum Zs values in a TT earthing system

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)

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

17th Edition Online Training : 2016

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

Part P and other Building Regulations

If you carry out electrical installations dwellings in England, Scotland or Wales not only are you expected to be able to comply with the HASAWA ‘risk assessments, safe working practices etc’ the EAWR ‘demonstrated by compliance with BS7671’ but also any relevant parts of the Building Regulations for example… Part A: Structural – Depth of cases, positions and sizes of holes and notches. … Read more

Domestic Maximum Demand

BS7671 Part 3 Chapter 31 Purpose, Supplies and Structure 311 Maximum Demand and Diversity Regulation 311.1 …….. In determining the maximum demand of an installation diversity may be taken into account. What this means is that not everything will be switched on at the same time and we can make allowances for that. Domestic installations: Applying … Read more

Risk Assessment Basics…

Companies have a legal duty to ensure that suitable arrangements are in place to manage health and safety. Documented risk assessments must be made if the company employs 5 or more people and these records must be kept. Basically: Assess the possible risks. Determine the possible consequences. Who or what will be affected. Evaluate the … Read more

Zs Values and Cmin

In a TN earthing system the cornerstone of protection against electric shock is that the protective device ‘circuit breaker’ shall not exceed it’s maximum disconnection time. For a 230 v to earth TN system (covers both single phase and 3-phase) that is 0.4 seconds (final circuits less than or equal to 32A) see T41.1  and 5 seconds (distribution circuits and >32A) see … Read more

Safe Isolation Save Lives

The following safe isolation procedure could save your life. If you have no experience and/or knowledge then you can’t avoid the dangers that are present and you should not be working on any electrical circuits or equipment. If in doubt always consult a competent (electrically skilled) person. Select an approved tester (see GS38). Inspect to … Read more