Max Demand

[Traineeboy]

Max demand 

Am I right is thinking if I wanted to work out the max demand of an install the following would be a good rule of thumb. 

40 A - cooker 

32A - ring 

32A - ring 

6A - lights 

20A - radial 

32A - ring 

6A - lights 

6A - smoke 

40 + (0.4 x 32+32+6 + 20 + 32 + 6 + 6 ) = 93.6A

I understand that there are rules to diversity in BS7671 depending upon the type of circuit but is the above calculation an accepted method ? 

But I also guess that if you turned on a fair amount of the appliances and put a clamp meter round the tails , this is also an acceptable method to work out max demand ? 

 

[Badger]

Generally you apply diversity as most people wouldn't be using all the appliances on full load at the same time in the same day so generally the loading is about 50% from how I understand things 

 

[binky]

Max demand 

Am I right is thinking if I wanted to work out the max demand of an install the following would be a good rule of thumb. 

40 A - cooker 

32A - ring 

32A - ring 

6A - lights 

20A - radial 

32A - ring 

6A - lights 

6A - smoke 

40 + (0.4 x 32+32+6 + 20 + 32 + 6 + 6 ) = 93.6A

I understand that there are rules to diversity in BS7671 depending upon the type of circuit but is the above calculation an accepted method ? 

But I also guess that if you turned on a fair amount of the appliances and put a clamp meter round the tails , this is also an acceptable method to work out max demand ? 

DNOs use the 40% rule, ie add up all the ccts and times by 0.4, which it looks like you have done. This is acceptable, but, to be frank I gave up on diversity a long time ago for the simple reason the more ccts you put in the bigger the unrealistic number you get. When I wire / rewire a house, I like to put in lots of ccts, eg a separate cct for the central heating boiler / any outdoor stuff / kitchen, as well as the usual up and down scokets and lights. So these days I tend to asess the likely loading by the appliances rather than ccts. 

 

[Badger]

Just because there's 19 ccts in a property (wonder who could have that many)

It doesn't mean there's more loading its just there's less things going off if something has a fault 

 

[SPECIAL LOCATION]

That 100% of the largest circuit + 40% of remaining circuits method, (from appending A of the OSG),

isn't a very good rule of thumb in my opinion. 

If a hypothetical traditional 4circuit wylex fusebox,  2x30A, 1x15A, 1x5A..   [ cooker/sockets/imm heat/lights ]

was swapped out for a new CU with:

32A cooker

32A Sockets d/s ring

20A Sockets u/s radial

16A Imm heat

6A Lights d/s

6A Lights u/s

6A Lights loft + TV amp

The rule of thumb max demand would increase from 55A to 66.4A, just because the CU was installed!!

and the typical reduced loading of modern LED lighting, mean the rule of thumb figures are way out.. 

You have to do your own assessment of what's connected..

and how many people are using what's connected simultaneously..  

BS7671 does NOT give rules for diversity..   there is guidance for some suggested allowances..

But if you read 2nd paragraph of Appendix A in the OSG (pg121)

it states that it is impossible to specify allowances for all types of installation.

(this comment & guidance is also found in Guidance note 1, selection & erection) 

It is one of those areas where your own knowledge of that particular installation takes priority over numbers from tables in books.

Guinness

 

[Badger]

That 100% of the largest circuit + 40% of remaining circuits method, (from appending A of the OSG),

isn't a very good rule of thumb in my opinion. 

If a hypothetical traditional 4circuit wylex fusebox,  2x30A, 1x15A, 1x5A..   [ cooker/sockets/imm heat/lights ]

was swapped out for a new CU with:

32A cooker

32A Sockets d/s ring

20A Sockets u/s radial

16A Imm heat

6A Lights d/s

6A Lights u/s

6A Lights loft + TV amp

The rule of thumb max demand would increase from 55A to 66.4A, just because the CU was installed!!

and the typical reduced loading of modern LED lighting, mean the rule of thumb figures are way out.. 

You have to do your own assessment of what's connected..

and how many people are using what's connected simultaneously..  

BS7671 does NOT give rules for diversity..   there is guidance for some suggested allowances..

But if you read 2nd paragraph of Appendix A in the OSG (pg121)

it states that it is impossible to specify allowances for all types of installation.

(this comment & guidance is also found in Guidance note 1, selection & erection) 

It is one of those areas where your own knowledge of that particular installation takes priority over numbers from tables in books.

Guinness

Our usage over the last 24 hours per hour is showed as the following form our electricity monitor but we srw on average about 5 amps total load and have pond

Fish tank

shed  and greenhouse

cctv

networking

server computer

printer x2

Laptops x5 

Plus tvs etc 











So diversity can't be amounted to a single type of instalation as you have to make a judgement for each property and environment