maximum demand

[ample current]

when working out the maximum demand am I right that it should be below 100A

Just working one out on a job and find the lighting comes to 4.5A
cooker comes to 22.5A (no cooker there to check actual consumption so assumed 8000w)
shower comes to 38A
and the power is 58A assuming i have worked it out right considering i haven't the slightiest clue of what is actually going to be plugged in
I have used all 32A od 1 circuit and 40% of 32 each of the other 2 so 32A + 13 +13 =58
toatal is therfore 123A

unless i have missed something staring me in the face and this isnt a big system so im a lil baffled

thanks in advance guys

 

[worzol99]

But when is it likely that all are going to be on at the same time

 

[telectrix]

max. demand is so hit and miss. do you really think that 3 RFCs will pull 58A between them? the kitchen RFC might pull 20+ A, while the others are probably powering a TV, PC, and a few other low power devices, all together <5A. if the suppliers fuase is 100A then on your cert. the max. demand is entered as 100A.

 

[jumpin jax]

There is very little chance , if this is a house , that the maximum you would draw would be 65-75 amps and that would be if they were cooking whilst having a shower with the iron, kettle on. And that being for about 15 minutes. Maximum Demand is more of a sensible educated guess not a mathematical equation.

 

[JD6400]

max. demand is so hit and miss. do you really think that 3 RFCs will pull 58A between them? the kitchen RFC might pull 20+ A, while the others are probably powering a TV, PC, and a few other low power devices, all together <5A. if the suppliers fuase is 100A then on your cert. the max. demand is entered as 100A.

Tel , rightly or wrongly this is how i always enter max demand as well but when ever i have asked any scam's r us they say that it is wrong !?

 

[Octopus]

Add up all the MCB values and multiply by 0.4

There are more circuits these days so the old fashioned way of calculating maximum demand is way out of touch IMHO

 

[telectrix]

Tel , rightly or wrongly this is how i always enter max demand as well but when ever i have asked any scam's r us they say that it is wrong !?

then it's time these scam providers entered the real world.

 

[dagrat]

Add up all the MCB values and multiply by 0.4

There are more circuits these days so the old fashioned way of calculating maximum demand is way out of touch IMHO

Totally agree, IMO it's only relevant on new supply at design stage.
There are three possible methods on an existing installation and they are: (1) use size of supply (2) multiply sum of all mobs by 0.4 As Murdoch says, and (3) switch on all load and clamp it

 

[SirKit Breaker]

when working out the maximum demand am I right that it should be below 100A

No. Maximum demand is what it is. But to save yourself weeks and weeks of calculations, just add up the sum of all the breaker values, and multiply it by 0.4, heyho, the figure is near enough your maximum demand. Stick the figure in the appropriate box, and go for a beer.

Example: MCB Values, 6,6,6,6,16,16,20,32,32,40,40 add the lot together = 220a, multiply by 0.4 = 88a, this your maximum demand. Someone many years ago, must have sat down and worked this out so we dont have to. We are not designers (well most of us), and this only really becomes important, and needs to be accurate if you are going to design a complex installation like a Hospital. For your average 3 bed semi, its not an issue.

Cheers...........Howard

 

[ezzzekiel]

highest load and then 40% of remainder, and still pointless

 

[monkeyelectric]

I just write down the supply fuse size unless it is likely to be below that value

 

[GLENNSPARK]

Tel , rightly or wrongly this is how i always enter max demand as well but when ever i have asked any scam's r us they say that it is wrong !?

well i had that n all...from my elecsa `assessor`.......i thought it was a load of old cobblers then...and i do now....
lets take earthing arrangements for example.....say its a TN-C-S....and its an initial verification.....so is it the measured value of Ze..or max. allowed value of Ze you would put down?....
of course its the max. allowed value.....lol....

 

[telectrix]

well, of course, 4 years training followed by 30 years practical experience, and we're not capable of sticking 2 insulated probes onto 2 terminals coz theyy are LIVE.

 

[ample current]

Thanks for your thoughts guys, not only me who thinks this is bit daft then.