Maximum Demand and Diversity Calculation Explained - BS 7671 On-Site Guide Appendix A
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- Опубликовано: 12 июн 2024
- 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
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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.
Thanks for taking the time to give such a detailed comment it is very much appreciated. Gaz 👍🏻
@@GSHElectrical I agree Gaz in fact if you do a continuous actual load assessment and I have done that on my property at least here in the US it rarely gets over a third actual usage of the total cut-out size. And we have larger motors and load here in the US in residential settings that run large AC and forced air heating units.
Craig, I am a new electrical design engineer and tend to do a lot of load calculations. Could you walk me through or tell me where I can find the DNO ADMD calculations please? I can give you my email if it’s easier
At last, easily explained and also appreciated comments from former DNO engineer
Massive thanks for watching and commenting 👍🏻
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 👍
Massive thanks for the kind words and watching 👍🏻
You just explained this better in 5 min than my teacher in 30 minutes thanks for keeping it lemon🍋👈 appreciate it geez
Thank you so very much for taking time to explain to me how to calculate maximum demand and diversity. Great video and thumbs up.
Thanks for watching and commenting 👍🏻
Very important subject explained expertly as no-one wants their Meter Tails glowing red hot
Great video, a very clear and concise explanation. Thank you
Fantastic video, simple and informal. Thanks guys!
Thanks for the support 👍🏻
Nice easy to follow explanation. Ideal method for a quick tally up to put on an EIC. Cheers!
Thanks 👍🏻
Excellent video, Marcus. Easy to understand. Thanks a lot 👍
Thanks 👍🏻
Arh. A sensible and easy way of doing it.
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
Another brilliant video from the best sparkies on you tube.
Thanks so much for helping me get qualified.
Thanks for sharing it with us
Nice one Marcus 🙌🏻 well explained love it!!👌👌
Thanks 👍🏻
Good video, nice and clear.
Thanks
Great video, cheers
Thanks 👍🏻
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?
Thanks
That’s very kind. Massive thanks Gaz
As always a great video and appreciated. Just a query though, diversity seems to have been applied to the two additional storage heaters? I thought no diversity allowed for storage heaters? There is a shower in the circuit as well as other panel heaters. Diversity seems to have been applied to these as well?
Any help welcomed. Thanks guys
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
Great video . But what about working out three phase ? I imagine it would be the same process but devide the answer by three ?
Is this the same approach if you have a submain in an annex if it’s run from an mcb from the main board; or if it’s fed from a Henley block, would you perform this same calculation for each submain consumer unit and add them together?
Sorry, just a query.
Isn’t current demand the current drawn by the connected equipment not the size of the protective device?
Using the protective device size gives a high max demand.
A 2kw heater would normally be installed on a 16 A radial but will only draw approx 8 A and is usually protected by a 13A fused spur. So you would be doubling the expected load by using the PD.
After calculating the Final circuit diversity, can we install a circuit breaker with a lower power to the consumer unit? e.g. 40A CB change to 32A CB after diversity calculation.
What would be the scenario if the calculations worked out to be over the 100A main fuse (example 117A ) ?
So how do you convert that figure to kva. What’s the recommendation solution if you go above the actual main fuse size. Thanks
Great video. What about for installations in schools or big office etc please?
We will produce more content on this in the future 👍🏻
I have a couple of queries for a board change I will be doing soon.
The new board has an spd supplied via a 40a mcb.
Am I correct in thinking that I can ignore that mcb for the calculation? My reasoning being that it is not drawing a load, it is just there to protect the spd.
I have a second 40a rcbo which feeds a garage cu with a 16a and 6a mcb’s in it would you count that as 40a or 22a for the calculation?
Please i want to ask you this question; what's the right order in which you should arrange your circuit breaker in your consumer unit. should it be from the lowest breaker to the highest or highest breaker to the lowest and why... Thanks
I am not an professional just started watching when my house was been rewired to make sure I knew enough to know if it was been done according to code and enjoyed the videos, one thing I was wondering is how do you know its a 100a fuse in there, My cutout said it was 100a but when the DNO removed it to allow the rewire to take place it was only an 80a fuse installed in the holder (had a complete rewire as house as my wiring was 2 core rubber stuff from the 50s with only 2 circuits for the whole 4 bedroom house)
You dont know. Unless you take the cover off (which should only be done by the DNO really) there could be a metal bolt in there for all you know.
@@creativejamieplays7185 so in the video example you could easly be drawing more A than an 80a fuse is rated for but you wouldn't know as you think its a 100a fuse, isnt that going to make the fuse blow? Or worse
in reality the max demand is unlikely to be anywhere near 88A. Sometimes I think the guidance has not kept up with some of energy savings now available e.g. for a 3-bed house, instead of using a 1000W for lighting it is now likely to be closer to 100W.
The calculation is a very basic albeit quick for onsite use. It might give you idea if you need to do a more detailed design. In any event one of the regulations is to determine the supply characteristics. The rating of the over-current protective device is just one characteristics. The info should be provided by the distributors, in reality this is harder than you think. In your case when the DNO removed the fuse you/your electrician were able to determine rating of the over-current protective device.
Just reading Craig’s comment, (1 year ago!) and I would agree that the 20+ kW seems excessive. The wording on the appendix A guidelines mentions maximum current demand, but the calculations shown are using the breaking ratings. If we know the attached loads, or at least their rating, I.e. storage heater, 3.5KW, oven 3.3kW etc. could these figures be used to calculate circuit maximum demand point loadS? The ring final circuit, I understand, we should consider worst case, and therefore likely to be the highest figure, but if we were to take the 40% of actual max demand loads, the overall figure is a more realistic load for a dwelling. Given that most “boiler” plate ratings for appliances are in excess of actual loads, there is already some float from the start.
So a cooker circuit would have diversity applied before applying whole diversity?
Very well explained. But when you say 40% of the remaining, do you mean 40% off total remaining or 40% off each off the remaining? . Fantastic video Marcos as always 👍👍👍❤️
You will get the same value
@@crisislord00 still not clear.
Sorry I have never been good at doing percentages. So I need it to be explained to me
@@seandempsey7351 add the full amounts together then 40% of that. It was explained in the video when they wrote it down, you can see they added and got the full amount and then 40% of that final value.
@@michaels8336 thank you if using the calculator on my phone am I right in thinking 40% would be 0.4
thanks for the video , one question! I have calculated the 40% out of 140 on your second calculation and it comes to 84 not 56 as you said. this means the amount taken has to be much more then 40% .
am I missing something ?
Yes your maths is wrong. 0.4 x 140 = 56
56+32 = 88Amps
Hi. I worked out, thinking about fitting a new CU to be 85.6a, however my main DNO is an 80a. Would you apply any more diversity or put a 100a in.?
Cheers
The IET Guidance Notes has more details on MD 👍🏻
What about cooker circuits/lighting and all the other rows in Appendix A Table A2 in the OSG?
Is this just for a quick calculation when doing an EICR?
The 100% of largest then 40% of remaining circuits is shown in row 9 of that table, I absolutely accept that it's correct, but I don't understand when I'm supposed to apply the info shown in rows 1-8 of that table, based on this video.
Great videos anyway thank you for making them.
Im confused i thought you had to do diffraction diversity factors for different circuits for example 66% of lighting circuits etc
Standard circuit arrangement On-site Guide Appendix A table A2 indent 9. 100% of the largest circuit 40% of the remaining circuits as stated in the video 👍🏻. Thanks for commenting and watching
So after diversity applied you totalled 88amps. What if this had a 60amp cut out fuse, as the majority of older single phase installations have?
The md calculation in osg is a bit… well … wrong really!! We’d be popping dno fuses all the time the md were anything near what most calculations total.
God help the calculations (and dno fuses) when EV really takes off!!
Great video chaps👍
Have a look at the pinned comment 👍🏻. There are other ways of carrying out the MD calculation but you have a great point about 60 amp cutout fuses and EV cars hence you have to tell the DSO (formally DNO) when you want to install an EV point.
eFixx you really need to sort your channel out your getting comments from idiots giving links to pornography websites . I don’t want to see this crap
report the comment like i have. it's all over youtube. we need to keep on reporting it.
This channel is NOT eFIXX 👀. All spam messages have been reported… THIS CHANNEL IS GSH ELECTRICAL 👍🏻
All channels get this now, youtube needs to stop the bots spamming
@@GSHElectrical yes it’s on your channel as well .
You mucky pup, stop clicking the links
Correct.... But we all know it's still nonsense 😂