Maximum demand and diversity

[voltage]

Hello all

I've got my NICEIC inspection in about 8 weeks time so i can hopefully join up with the NICEIC if all goes to plan.
For the major im doing a consumer unit change at my mum and dads house ive spoke to western power they are coming out soon to fit an isolator in the line so i can safely isolate the incoming tails from the supply.

Now this is not a new installation but im still working out all my demand and diversity for each of the circuits.

I would appreciate a little guideance or help from the fellow electricians on here thanks.


The list so far

Lighting circuit downstairs

1250watt is total wattage of all lights downstairs

1250/230 = 5.43amps then i have to add 66% of total current demand
5.43 x 0.66 = 3.58amps
cable selection
1.0mm carrys 16 amp 1.5mm carrys 20amp clipped direct even in worse case scenario ref methods both of these cables will be ok
MCB type B 6amp


Lighting circuit upstairs

620 watt is total wattage of all lights upstairs
620/230 = 2.6amps then i add 66% of total current demand
2.6 x 0.66 = 1.7 amps
Cable selection
1.0mm carrys 16amp 1.5mm carrys 20amp clipped direct even in worst case scenario ref methods both of these cables will be ok
MCB type B 6amp

Cooker and Hob built in

10.7kw

10700 / 230 = 46.5amps
46.5 - 10amps = 36.5amps
36.5 x 0.3 = 10.95amps
10.95 plus the 10 amp we took off 10.95 + 10 = 20.95
+ 5 amps as the cooker switch has a socket incorporated = 25.95 amps
MCB 32amp type B
cable 6mm or 10mm to supply the cooker

immersion heater

3kw
3000 / 230 = 13amps
MCB 16amp type B
cable 1.5mm or 2.5mm

Ring circuit downstairs

7000 watts total
7000 / 230 = 28.7amps this is where im not to sure in OSG it says 100% of current demand of largest circuit + 40% of current demand of every other circuit

so is this correct
28.7 amps round up to 29
29 x 0.4 = 11.6amps
29 + 11.6 = 40.6amps ?

or is it
32 amp for mcb
32 x 0.4 = 12.8
32 + 12.8 = 44.8amps ?

if so seems as though its a ring its unliklely all sockets and appliances will be on downstairs all at the same time so a 32 amp MCB would be ok ?

any help or understanding on this would be great many thanks.

 

[IQ Electrical]

The good book states: "The use of other methods of determining maximum demand is not precluded where specified by a competent person"

This translated means that you as designer are not limited to the rigid factors as per the On-Site Guide etc. Your knowledge of the installation and it's use will probably enable you to work out a far more accurate figure based on what you have seen.

I can tell you from experience and load monitor/power quality tests that we carry out, stated maximum demand figures are normally way in excess of what small domestic installations actually measure out at.

Also, don't forget that all maximum demand figures are 'estimates' and the NICEIC are perfectly aware of this.

 

[voltage]

thanks for the reply but on the last sum of the downstairs ring is where im a bit confussed could you tell me which of the two equations is correct plz manny thanks

 

[Engineer54]

thanks for the reply but on the last sum of the downstairs ring is where im a bit confussed could you tell me which of the two equations is correct plz manny thanks

As regards to your Ring Circuits, if you had 3 such rings, say one for the Kitchen, one for downstairs and one for upstairs. Then you would take the ring circuit that is going to be the most heavily loaded, say the kitchen ring. That you will take as the 100% (7000W) circuit, the other 2 rings would be taken at 40% of the 7000W. You then total up the power demand in this case 29A + 11.6A + 11.6A = 52.2A for all 3 circuits which you would then add to all the other calculated totals.

It can be calculated in this way, or by MCB ratings x 0.4.. Which ever way you calculate, it will only ever be a course estimated figure. So yes, your rough calculation methods are correct....


EDIT ....Why would you use a 10mm cable for a cooker load of 26A?? Future proofing??

 

[domestic spark]

Add up all breaker amperages, and x by 0.4 so much easier, as engineer says an estimate, if your still over, then take off biggest breaker size also, I've never come across a main fuse that has blown due to being overloaded hope this helps

 

[voltage]

thanks guys for the replies made it more clear now. As to the 10mm for cooker yeah was thinking of future proofing

 

[domestic spark]

Let me know how your nic inspec goes won't you

 

[voltage]

Add up all breaker amperages, and x by 0.4 so much easier, as engineer says an estimate, if your still over, then take off biggest breaker size also, I've never come across a main fuse that has blown due to being overloaded hope this helps

This way of adding up all the breaker amperages and then x by 0.4 is alot easier thanks very much. Just one question though dont different circuits require different percentages eg lighting 66% cooking 30% heating and power 50% . How does applying 40% for all apply if you could explain that would be very helpfull many thanks.

Reguarding the NICEIC Inspection sure i will let you know how i get on.

 

[domestic spark]

This way of adding up all the breaker amperages and then x by 0.4 is alot easier thanks very much. Just one question though dont different circuits require different percentages eg lighting 66% cooking 30% heating and power 50% . How does applying 40% for all apply if you could explain that would be very helpfull many thanks.

Reguarding the NICEIC Inspection sure i will let you know how i get on.

its only a VERY VAGUE guide. you as an electrician would have a much better knowledge on site. its a rough guide only, nic know this too, soo you will be fine

 

[domestic spark]

and as you said some circuits no diversity, others different percentages, its an averages calculation.