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max demand


paul b b

Question

hi chaps.

can you just check my workings out please.

2 x rings

1x 9.5kw shower

1x cooker

1x combi boiler

11 lights

2x smoke detectors

thanks

paul

also is the form after diversity?

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22 answers to this question

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If your answer is over 100A you've done it wrong!

Realistically what will be plugged in and used? What's a real expected load?

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If your answer is over 100A you've done it wrong!

Realistically what will be plugged in and used? What's a real expected load?

But what do you write in the box on the form?

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how do you work out ring diversity?

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Paul don't take this the wrong way but I think you need to buy a book on electrical installation , no offence intended , just trying to help.

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Paul don't take this the wrong way but I think you need to buy a book on electrical installation , no offence intended , just trying to help.

thanks evans!!!

i have a book just getting stressed out about filling in this form as its for the assesser

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Ah stressful time for all of us M8.

Rough guide to maximum demand is add the value of all the MCB,s and multiply by 0.43

I think thats the figure, Green Hornet will confirm, I filched it from him.

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there is no hard and fast rule to it, its your decision, so if you record a sensible figure i dont think anyone can call you wrong.

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Ah stressful time for all of us M8.

Rough guide to maximum demand is add the value of all the MCB,s and multiply by 0.43

I think thats the figure, Green Hornet will confirm, I filched it from him.

ahhh thats intresting, a much quicker way of working out.

thanks.

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Something like that ,Meady, its in the Big Red Boring book somewhere .

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yeah I see that in the OSG page 97 (but all of my sockets are the same size- hohoho)

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Ah stressful time for all of us M8.

Rough guide to maximum demand is add the value of all the MCB,s and multiply by 0.43

I think thats the figure, Green Hornet will confirm, I filched it from him.

But it has been said this doesn't really work so well any more. The reason being we split the house into more circuits for convenience and to minimise nusance tripping. Eg old house may have Up ring, Down ring, 1 lighting circuit, cooker, shower, immersion heater. Rewire same house we have up ring, down ring, kitchen radial, utility radial, up lights, down lights, outside lights, smoke alarms, shower, immersion, cooker. So we shoot up from 6 circuits to 11.

Using Deke's magic number

Initially 30,30,5,30,30,15 = 140A * .43 = 60.2A

Now 32,32,16,16,6,6,6,6,32,16,32 = 216A * 92.88A

realistically we havn't started using an extra 33A!

Do you see what I mean?

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But it has been said this doesn't really work so well any more. The reason being we split the house into more circuits for convenience and to minimise nusance tripping. Eg old house may have Up ring, Down ring, 1 lighting circuit, cooker, shower, immersion heater. Rewire same house we have up ring, down ring, kitchen radial, utility radial, up lights, down lights, outside lights, smoke alarms, shower, immersion, cooker. So we shoot up from 6 circuits to 11.

Using Deke's magic number

Initially 30,30,5,30,30,15 = 140A * .43 = 60.2A

Now 32,32,16,16,6,6,6,6,32,16,32 = 216A * 92.88A

realistically we havn't started using an extra 33A!

Do you see what I mean?

yeah.

awwww these bloody forms GURRRRRR!!!

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Single phase 100A fuse I just put 100A as load.

AndyGuiness Drink

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But it has been said this doesn't really work so well any more. The reason being we split the house into more circuits for convenience and to minimise nusance tripping. Eg old house may have Up ring, Down ring, 1 lighting circuit, cooker, shower, immersion heater. Rewire same house we have up ring, down ring, kitchen radial, utility radial, up lights, down lights, outside lights, smoke alarms, shower, immersion, cooker. So we shoot up from 6 circuits to 11.

Using Deke's magic number

Initially 30,30,5,30,30,15 = 140A * .43 = 60.2A

Now 32,32,16,16,6,6,6,6,32,16,32 = 216A * 92.88A

realistically we havn't started using an extra 33A!

Do you see what I mean?

Good point Patch, I blame the Hornet for this ,he,s flogged us a damp squib.

Go back to guessing it then !! :|:coat

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hi chaps.

can you just check my workings out please.

2 x rings

1x 9.5kw shower

1x cooker

1x combi boiler

11 lights

2x smoke detectors

thanks

paul

also is the form after diversity?

We could check your workings out...................

If you had given us some workings out to check???:|:(

Appliance ratings?

No of light fittings wattages etc..?

i.e. 10 x low energy 7watt bulbs....

has less MAX DEMAND than 10 x 100watt bog standard bulbs?

How many people live in the property?

how many appliances will realistically by simultaneously switched on?

I could wire a house with 20 radial circuits @ 15amp each..

or put them all onto one rings @ 32amp.

The NUMBER OF CIRCUITS does NOT determine the max demand.

The number of persons using the appliances and equipment over a sustained simultaneous period DOES affect the max demand...

e.g.

consider a cooker taking 8000watt.. (approx 35 amps)

and a shower taking 9500watts.. (approx 41amps)

IF they are never switched on together the max demand will never exceed 41amps....

IF they are both on together for a sustained period of time the max demand could be 70amps +

(ignoring diversity with the cooker for the above example)

If the home only has ONE person living in it.... unlikely to both be on together...

If the home has a family of FIVE... greater probability of simultaneous usage!

If you read the BS7671 guidance about Max Demand it states quite clearly it is the INSTALLATION DESIGNER who will best be able to asses the realistic max loadings per circuits and any appropriate diversity factors to be applied!

THE IS NO STRICT RULE TO DEFINE MAX DEMAND AND DIVERSITY THAT CAN BE UNIVERSALLY APPLIED TO EVERY INSTALLATION!;):|

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But it has been said this doesn't really work so well any more. The reason being we split the house into more circuits for convenience and to minimise nusance tripping. Eg old house may have Up ring, Down ring, 1 lighting circuit, cooker, shower, immersion heater. Rewire same house we have up ring, down ring, kitchen radial, utility radial, up lights, down lights, outside lights, smoke alarms, shower, immersion, cooker. So we shoot up from 6 circuits to 11.

Using Deke's magic number

Initially 30,30,5,30,30,15 = 140A * .43 = 60.2A

Now 32,32,16,16,6,6,6,6,32,16,32 = 216A * 92.88A

realistically we havn't started using an extra 33A!

Do you see what I mean?

The vet-cow-man thingy has been taking on board his learning very well.....

he speaks the wise words as spake previously on this ere forumbulator!

Guiness DrinkGuiness DrinkGuiness DrinkGuiness Drink:D:xApplaud Smiley

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The vet-cow-man thingy has been taking on board his learning very well.....

he speaks the wise words as spake previously on this ere forumbulator!

Guiness DrinkGuiness DrinkGuiness DrinkGuiness Drink:D:xApplaud Smiley

I learned!

We've had this before and I couldn't find the thread.

:D

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Good point Patch, I blame the Hornet for this ,he,s flogged us a damp squib.

Go back to guessing it then !! :|:coat

ROTFWL

The calculation I use is a general and effective way of calculating on an exsisting installation, the figure I use is 0.42.

The real difference is at best negligable, and is ample for PIR or small EIC certificates.

For a new installation I never use this method as I prefer to design the loading not work up to it.

The correct way( ? )to do it is to use the BRB or OSG, however you will note that it says any other means can be used providing the figures are realistic.

We had a post not far back where my method was more or less within 5 amps or so,of other methods used.

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