Maximum Demand and Diversity Calculation Explained - BS 7671 On-Site Guide Appendix A

In this video we go through step by step the calculation for working out maximum demand and diversity for a single phase installation. For this version of the calculation we take 100% of the largest circuit fuse rating and 40% of the sun of all the other fuse ratings and add these numbers together to find the maximum demand for the installation.

== 🕐 Time Stamps - Cut to the action 🕕 ==

00:00 - Maximum demand and diversity
00:18 - Easy calculation on-site
00:38 - Old circuits
00:47 - New heaters
01:10 - Don't want to blow the 100 amps fuse
01:33 - 100% of the largest circuit
01:42 - 40% of the remainder
02:04 - Circuit loads without diversity
02:33 - Applying diversity to the old circuits
03:23 - Applying diversity to the new circuits
04:08 - Table in the On-Site Guide
04:21 - Comparing calculations

Videos are training aids for City and Guilds (C and G) and EAL courses Level 1, 2, 3 plus AM2, AM2S and AM2E.

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[protectiongeek]

As a former DNO engineer, who spent about two years in distribution network design, most of it on LV networks, I never fail to be surprised at how high the After Diversity Maximum Demand (ADMD) for a domestic property turns out to be using the BS7671 criteria. 88A, single-phase assuming nominal supply voltage of 230V yields the ADMD as 20.2kW - this is well into three-phase supply territory!!! 20kW for a one-bed house is just nonsense. Don't misunderstand me, GSH Electrical appear to have correctly applied the criteria set out in the regs, but from a DNO perspective if the same criteria were used, the LV networks would be massively over-specified. And, yes, I know that a further degree of diversity applies for multiple properties, although they do tend to demonstrate remarkably similar load curves.

As a matter of interest, I downloaded the latest version of my local DNOs spec' detailing ADMD calculations and - making some assumptions about the number/rating of the space and water heating appliances - the ADMD for this property falls out at 8.2kW (35.6A). I still think that's probably a bit high tbh but it's a lot closer to reality than BS7571 would have us accept.

[pauledwards]

At last, easily explained and also appreciated comments from former DNO engineer

[adrianupnorth]

I just love GSH training. A newbie learning for the first time to an old timer on CPD or just refreshing the memory you explain things in plain English. Keep up the good work 👍

[scarcxy]

Thank you so very much for taking time to explain to me how to calculate maximum demand and diversity. Great video and thumbs up.

[garythespark]

Nice easy to follow explanation. Ideal method for a quick tally up to put on an EIC. Cheers!

[therealdojj]

that's a great help because i've just checked my numbers and the answer is 104.8!
although that includes the 40a for the garage which i think is a little excessive so i'll drop that to a 32 and drop the 32's for the sockets down to 16 as that should make things within specs as it brings it down to 91.2 on our 100amp main
ok, so that just means more stuff to do to fix this house of electrical horrors

[POLEinTheUK]

Great video, a very clear and concise explanation. Thank you

[BobBobOnYouTube]

Excellent video, Marcus. Easy to understand. Thanks a lot 👍

[terryleebarrett]

You just explained this better in 5 min than my teacher in 30 minutes thanks for keeping it lemon🍋👈 appreciate it geez

[James_scott]

Fantastic video, simple and informal. Thanks guys!

[AndyK.]

Arh. A sensible and easy way of doing it.

[Mike_]

Very important subject explained expertly as no-one wants their Meter Tails glowing red hot

[peleuwase]

Nice video, just to clarify, I have noticed that you have applied 40% to all the remaining circuits, according to the OSG, no diversity allowed on shower circuit?

[kingofthetrowel]

Nice one Marcus 🙌🏻 well explained love it!!👌👌

[daverose]

Another brilliant video from the best sparkies on you tube.
Thanks so much for helping me get qualified.

[johna]

Great video
Any advice would be welcome I'm thinking of connecting an induction hob and oven to the same cooker outlet. Hob is 7.5 kw and. Oven is 3.5 kw so around 11kw. I'm using 6mm cable over around 6 meters to a 32 breaker no ring just direct.
Thanks

[alanmarriott]

Very good video but could you explain or do another showing how you calculate diversity on a 3 phase board please when 3 phase and single phase circuits are in the DB. Thanks

[Edgariux]

Great video . But what about working out three phase ? I imagine it would be the same process but devide the answer by three ?

[OpsNngroup]

Hi i have just watched this video as a refresher. I am now confused as to when columnds 1-8 would apply in a domestic dwelling. Do we just use column 9 for Domestic premises?

[alanmarriott]

Great video. What about for installations in schools or big office etc please?