Diversity issue

[lost-sole]

I have a client who wants me to install more than your normal stuff in a new built garage but looking at his mains board in house he is already on his limits here's my findings and calculations please correct me if Iam wrong

existing mains board 6 x 6amp lighting = 36amp after diversity =23.76
40amp cooker circuit after diversity =19amps 3 x 32amp final circuits after diversity = 57.6amps

he wants in garage

20amp for 2x 2.5kw heaters 16amp for radial sockets 16 amp for some fancy energy saving water heater from zip to supply shower 6amp for lighting i have added these to the circuits in existing board for my calculations and came up with 125.12amps demand obviously with a 100amp cut out we are way over but iam for once hoping that i have got the calculations wrong can anyone help

thanks in advance

ANDREW

 

[acat]

Diversity works on the appliances and lights on the circuits. The method you are using is a rule of thumb method ie add all the MCBs up and divide by 4 if I remember Im sure someone will correct me if Im wrong

Hope that helps


Chris

 

[bugsy]

If you calculate on the actual lighting load as opposed to OCPD and number circuits you will proberbly find your under the 100a I cant see 8.2kw of lighting iin a dommestic

 

[flukey]

i was always taught to add up all breakers then x by 0.4

so 230 amps x 0.4 gives you 92 amps (ish)

 

[Des 56]

More than likely your way over the top with the actual loading that will take place
Taking the diversity guidelines off the ocpd usually ends up topping the 100 amp cut out fuse or more often than not the 60 amp fuse

A 100 amp 1361 taking 100 amp constant load may go for over 2 hours without popping
It would have to be one monster constant load to tip the scales for that fuse to give up the ghost

If you think the loading will be a problem,then try cranking up the load with as many of the appliances showers cookers kettle ( especially the kettle ) toaster ( to go with the cup of tea your making yourself)washer, dryer and the like and measure the current taken over a short period

Having bunged as many loads on as possible,you may be very surprised at how low the actual draw may be,even if it were monster as stated, it takes quite a while to pop

 

[steamboatwilly]

More than likely your way over the top with the actual loading that will take place
Taking the diversity guidelines off the ocpd usually ends up topping the 100 amp cut out fuse or more often than not the 60 amp fuse...

Yeah, agree entirely.

I just did some calculations at a large house locally and I wouldn't let them have a new electric shower because the load (calculated using OSG formula) was 185 amps! Turns out that the tails (which are long) have been protected by an 80amp fuse for years...and it's never blown. Diversity is an imprecise science.

 

[lost-sole]

Cheers guys i have always used the add all up x .40 but was doing it out of book

 

[lost-sole]

Cheers guys i have always used the adding up and x 0.40 but i was thinking of using this job on my next part P assessment so didn't want to create any issues

 

[ezzzekiel]

cant see it would, diversity is not really set in stone

 

[martysparky]

yea, bit of a guessing game really.

Good point about measuring the current after stacking the load I think.

Heavy duty functional test!


How many leckys say can't do it and then the power consumption it lower than if the work took place..

Part L springs too mind Conservation and use of power.

Just a thought

 

[acvc]

I've been reading this post because I'm about to turn down a job on the basis of maximum demand exceeding the 100A cut-out fuse.

I've got these ways on the CU:
Sockets x3 @32A = 57.6A / x1 @20A = 8A
Intruder Alarm and TV Amp x1 @6A = assuming load as 4A
Smokes x1 @6A = assuming 3A
Lights x2 @6A = 9A
Cooker x1 @32A = 21.6A (couldn't see actual rating).

Worryingly: x1 @16A labelled 'SPARE' but on. Couldn't identify any load/equipment.

Without the 'SPARE' then: Max Demand after diversity comes out at 103.2A, and the cooker could be a lower load too. BUT even so, the customer is asking for a feed to a new 13A water heater!

I read what you experienced guys are saying about loads and also the main fuse's breaking time, but Appendix 1 of the OSG states

"The current demand for any final circuit which is a standard circuit arrangement complying with Appendix 8 is the rated current of the overcurrent protective device of that circuit".


If I do it - which i don't feel like I should - how would I justify it to The Man From The NIC (or anyone) when he comes to assess my work?

 

[lost-sole]

Add them all together and x 0.40 (my ELECSA inspector was happy me using this calc) should be a demand of 68.8 amps plenty left there assuming the 16amp is a spare

 

[acvc]

Ta for that lost-sole.

I'm with you on that as it's a small-medium size house with no crazy-load equipment, and this case has highlighted to me how if you're a bit sloppy about selecting the right PD. and a bit sloppy about your separation of circuits, then you leave the next spark with a bit of a headache when it comes to calculatibg max demand.

Basically, PDs with unnecessarily high ratings, and/or an unnecessary number of circuits ...... distorts demand calulations BUT I don't feel comfy ignoring Appendix1 of OSG.

 

[cbw]

I turned down a similar kind of job.....For a 'friend'

She is a hairdresser and is converting her garage into a home salon, she wanted 4 double sockets for 2 fridge freezers (in side area) hair drier and curlers/clippers, fan heater this was fine, then she produced the 10Kw shower!!!!!!

In the house she has a 10.8kw shower, an electric range cooker etc........respectfully declined and she thinks I am a jobsworth!!!!

 

[GT1]

now i know its a bit geeky and sad... however. I have one of those British Gas energy meters, its essentialy a clamp meter which you put in the service box and fit to one of the meter tails, and it sends the data wirelessly to a little display meter in the house. With that you show your consumption in either pounds and pence per hour, or in KW.

So, after reading this thread i thought... hmmmmmmm i wonder.. so i went round the house and turned pretty much everything on..! which includes..
All the lights
Garage lights
computer
central heating
outside flood
oven
hob extractor fan + lights
toaster
kettle
iron
tumble drier

The only major things not turned on were
washing machine.. cant admit to knowing how to use it or the wife will give me work.
wifes hairdrier and hair straightener thingies.. (see above)
electric shower.. decommissioned i'm fitting a mixer shower as we speak..!


The peak on the display showed about 10.5KW..
thus 10500 / 240 volts (which it is at my place) = 44amps..

now in the old days my shower at 9.5 KW could have almost doubled that figure !!
But the likely hood of EVERYTHING else being on also would be very low indeed.

and just as a comparison.. the total of my MCBs in use would be 166amps if the shower was in use.
which times 0.4 = 66amps..

So although the 66 amp is well inside the 100 amp service fuse.. as people have said its not an exact science. Personaly i do use it as a guide, knowing its quite an artificialy high (therefore safe) figure to work from.