Cable calculation. Calculating the live cable size from BS 7671

This video is mainly aimed at students on Level 3 and Apprentices. The video shows a step by step method how to calculate the size on the live cable only using BS 7671. Each formula you need is shown and explained, each table used and page is shown in detail.
Finding Ib, In, It, Iz and all relevant C factors. Finding the reference methods, mV/A/m value and calculating volt drop.

[@ashleyhutton7046]

You are a legend, best video on cable calcs hands down.

[@ashleyhutton7046]

@@SpinSkins Would you know the formula on how to work out the Iz of a 4mm ring circuit?

[@ElectricalStudentsUK]

Thank you mate, glad my videos help you

[@Mega_sleepy]

Thanks for this video, I’ve just studied this but couldn’t get my head around it.

[@nickbanwell5771]

Could you please do a video on the tabs you’ve got on your regs book, looks so much easier to navigate. 🙏

[@HH-oi8hn]

Well done,excellent and clear explanation, may God bless you ,thanks

[@SpinSkins]

Thank you, I hope my explanations help with your learning journey

[@HH-oi8hn]

@@SpinSkins your explanation really helped me understand some things that were Ambiguous to me. Thanks 🙏

[@NaciMahmut-rf5xf]

Is that the 1st time you opened that regs book or do you keep it in a safe? Mine looks like a tiger was reading it.

[@HH-oi8hn]

Your handwriting beautiful

[@saviourattard8317]

😢😢😊

[@ElectricalStudentsUK]

Glad it has helped you. For an indepth, step by step, page by page guide, check out the shop www.electricalstudent.co.uk

[@gbelectricks]

At 19.27 you choose to put “In” on top of the equation. In this example, surely “Ib” can be used, as this is a fixed load (water heater), that cannot be overloaded?

[@ElectricalStudentsUK]

In short, no. Page 167 of the OSG gives you the equation of It>In divided by the C factors. Also Regulation 433.1.1 details how the In must nit exceed the Iz value. Which is found by In divided by the C factors

[@goaway9487]

@@ElectricalStudentsUK that might be ok in a class room, but your way is wasteful in a real install. you only use In for your CCC if you can overload the circuit. 433.1.1 says that your In must be less than It & it will be regardless of which one you use. The OSG is limited in most of its explanations because of the regs so it’s not written in stone that you have to use In.😂

[@eyazdani4537]

Minutes 13, should be written mV/A/M.

[@ElectricalStudentsUK]

Yes well spotted! Sorry for my mistake

[@eyazdani4537]

Thanks for your informative educational videos. 👍

[@ElectricalStudentsUK]

No worries mate. Anything you're unsure of and want me to go over for you, let me know

[@sasalotas]

Great video. Starting my lvl 3 next week

[@ElectricalStudentsUK]

This video will really help you, check out my level 3 formula videos when you start the maths and scientific principles module. There are formula sheets and a step by step cable calculations guide in my shop at www.electricalstudent.co.uk They will be really helpful to you

[@goaway9487]

You should be using Your design current as this circuit can’t be overloaded. 433.1.1 says you can as long as it’s a greater value than both design & protective device rating currents. Using your way is not very practical in the real world & leads to larger & more expensive cables when they’re not really needed.