How to Calculate the cable size and protective device rating

Electrical Installation Design
This is an older video. New video coming soon to clear this up
The term 'Iz' has been incorrectly used when it should be 'It''
The calculation method is still correct, however.
'It' is the value we find in BS7671 appendix 4 after we carry out out correction factor calculation.
The calculated value I have since discovered, has no name.
From BS76712
This method is used in items 5.1 and 5.2 and produces a value of current
and that value (or the next larger value) can be readily located in the
appropriate table of current-carrying capacity and the corresponding
cross-sectional area of conductor can be identified directly.
It should be noted that the value of It appearing against the chosen
cross-sectional area is not Iz. It is not necessary to know Iz where the
size of conductor is chosen by this method.
All rating factors affecting Iz (i.e. for factors for ambient temperature,
grouping and thermal insulation) can, if desired, be applied to the
values of It as multipliers. This involves a process of trial and error until
a cross-sectional area is reached so that Iz is not less than Ib and not
less than In of any protective device it is intended to select. I
n any event, if a rating factor for protection by a semi-enclosed
fuse is necessary, this has to be applied to In as a divisor.
It is therefore more convenient to apply all the rating factors to In as divisors.
This method is used in items 5.1 and 5.2 and produces a value of current
and that value (or the next larger value) can be readily located in the
appropriate table of current-carrying capacity and the corresponding
cross-sectional area of conductor can be identified directly.
It should be noted that the value of It appearing against the chosen
cross-sectional area is not Iz. It is not necessary to know Iz where the
size of conductor is chosen by this method.
How to carry out cable calculations to correctly size your electrical conductors
Design Current
Protective devices
Current carrying capacity
Volt drop
Sizing of the MCB/Fuse
and more...
At 21.29 you might spot I used the In instead of Ib in the volt drop calculation. So 16A instead of 13.04 A
Volt drop is actually 13.23v not 16.24v
Still unsuitable cable though
22.16 Maths error Ib x L

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[@JPElectric]

Thank you Nick for the nice comment

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The way you explained each and everything is simply amazing..

[@JPElectric]

Thanks very much appreciate it.

[@no_short_circuit]

Absolutely wonderful. As an adult learner I have watched many videos and read a lot about how to calculate cable size. The way you've explained it here (particularly the graphics) is the best I've seen and I'd recommend it to all apprentice electricians. Thanks for taking the time and I look forward to your future videos.

[@JPElectric]

Thanks very much for your comment. Really pleased you are finding these videos useful.

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[@JPElectric]

Thanks very much Danny

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superb video for apprentices and sparks alike. golden material for apprentices doing the design assignment for the city and guilds 5357 qualification

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This is excellent work you've done here. Much appreciated.

[@JPElectric]

Thanks for watching OulChap

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[@JPElectric]

Hi Emi Haji, Thanks for watching. pleased it helped you.

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[@JPElectric]

Wow, thanks!

[@balsamomahmoudian3279]

That's a wonderful video, well done.
One point, at the time 48:15, Ib=13.04 needs to be used instead of In=16, then correct Vd is 13.23v

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As a lecturer in Electrical Installation myself I can only agree with the sentiments expressed by others in the comments section. Your style and content is second to none . Would love the opportunity to speak with you , I’ve struggled to find any contact details.

[@JPElectric]

Thanks for the kind comment

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your're the best. that's it! thanks a million for your hard work to make this amazing tutorial. This was exactly what I was looking for.

[@JPElectric]

Thank you, for the kind comment

[@freezefoot]

This was your best yet. Best Domestic electrics tutorials on TH-cam.Took me a few days to get through it all. Your two previous comments below sum it all up.Adult Learner Question:@45:50 you mention table 4D2A and/or 4D5(flat twin and earth) and @46:00 similarly you refer to 4d2B and 4D5 .Can you use both tables interchangeably?Why no Reference B in 4D5 .I am not too sure what type of cable 4D2A refers to in a domestic situation.Thank you for this video.

[@JPElectric]

Thanks Freeze foot. Well done for getting through the whole video. I do think they might be a bit too long?
Table 4D5 is specifically for T&E in insulated stud walls, and above plasterboard ceilings, covered in insulation. So its for a very specific type of installation method.
The other table 4D2A Is for PVC/PVC insulated cable (Inner and outer insulation) so that would include twin and earth as well.
This table gives you a few more installation methods to choose from. You will notice the volt drop is the same in 4D5 and 4D2B

[@freezefoot]

I appreciate your reply and clarification.The length of the video may put others off but there was detail in this video that I had not seen in similar videos covering this topic so it is always a compromise.Look forward to your next video.

[@markadams3746]

What a fantastic video brilliant keep up the great work

[@JPElectric]

Thanks Mark appreciate it.

[@danielteyehuago1633]

Please apart from this MFT instrument, which other instrument can be use to determine the resistance value of a cable for for a distance of 1m

[@mikekingswood]

Absolutely brilliant video!

[@JPElectric]

Thanks Mike Appreciate it.

[@danielteyehuago1633]

Please apart from MFT, which instrument can be use to measure the cable resistance

[@powerprice-r1f]

26:43
Shouldn't the current for the orange line be the sum of both current so the voltage drop across orange line should be calculated with 16A?

[@paulord603]

Excellent guide. Thank you.

[@JPElectric]

Thank you Paul

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[@JPElectric]

Thank you linksone6287. Thats a really nice comment and I appreciate it. Emergency lighting would be a good subject to cover.

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Hello sir,
Should the outdoor service switch be greater or smaller than the main breaker in the consumer unit?
I'll be so grateful if you would send me back.
Thank you,
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Good video, I learned a lot watching it.

[@JPElectric]

Really please you found it useful, thanks for watching

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Simply great! - thanks.

[@JPElectric]

Thank you Marcus

[@RanjitGill-d4u]

Education at its finest

[@JPElectric]

Very kind of you to say so , thank you

[@imeprezime1285]

For 27 A current carrying capacity cable (with account of correction factors) , first standard fuse rating is 25 A. Not 20 A

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Two lamps are connected in series lamp A is rated 60W and lamp B is rated 100W. Which of this lamp will glow brighter if the supply voltage is 230V and why...
Again Which of this lamp will glow brighter if it is connected in parallel with 230V and why...

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Very good explanation

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Thanks

[@balsamomahmoudian3279]

correction: time 21:21

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Thanks for the thumbs up Mike, appreciate it.

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