ON-SITE GUIDE - APPENDIX F – PART 2 – VOLTAGE DROP - HOW TO CALCULATE IT – HOW TO SELECT CABLES

This is part 2 of our look at Appendix F of the On-Site Guide or OSG. This is an often under-used Appendix, but it is so full of very useful information. We are working to Amendment 2 of the Wiring Regulations, the brown book and all page numbers in this LearnElectrics video refer to the brown Amendment 2 On-Site Guide. The on-site guide follows the Wiring Regulations book BS7671 2018 Amendment 2. Over time, we’ve had lots of questions about voltage drop … What is voltage drop for instance … Where do we start with the formula, and can we have some examples to help us to understand? How does the formula work? How does it affect the circuit? And even … Why does it matter about voltage drop? A cable is just a cable … isn’t it? We will use a basic cooker circuit to show you how we get voltage drop and its effects on the circuit. There are worked examples for you to follow along with, all fully explained with lots of detail. We look at the standard formula and at a valuable re-arrangement that you can use in your work. Some of our very observant viewers have noticed a typo and brought this to my attention, for which I am truly grateful. On a couple of charts I have the Ohm’s law formula for current as I = V ÷ I which cannot be. This should be I = V ÷ R Ohm’s Law, as a reminder then … V = I x R I = V ÷ R R = V ÷ I And Power Law P = V x I V = P ÷ I I = P ÷ V This is video number 215 and to view all our videos type in LearnElectrics all one word into the YouTube search bar. Visit our YouTube channel where we have many more videos on a wide range of electrical topics.