Maximum Demand and Diversity.

[schmeagle]

Hi all.

I am now studying on a level 3 course and I really need some information upon this topic. The O,S,G is in front of me but for some reason I just cannot get my head around were it is saying about the % rates to apply.
I belive I am ok but when we get to the cooker and u take off 10A, do calc, then add 10A back on, pluss the standard arrangement of final circuits, I just get lost?

Can someone walk me through this in laymons terms as my tutor is moving about 200MPH on this topic and I could do with a head start.
Thanks for repies in advance.
Im sure it cant be this hard???

 

[riveralt]

Cooker = 9.5kw rating
9500/230v = 41.3 Amps = Max demand

Diversity = 10Amp + 30% of remaining plus 5amps if there is a socket in the cooker switch.

10 +(31.3*.3) = 19.4Amps +(5Amps if required for socket)

Ring final circuit = Full demand on first circuit - what MCB is 32Amps.
Then add 40% of remaining.

ie Two Ring final circuits on 32 Amp MCB

After Diversity = 32 + (.4*32) = 32 + 12.8 = 44.8Amps.

 

[PrinceofDarkness]

If your tutor is is moving at such a speed, then it's up to you to tell him to slow down. You shouln't have to fall back on the On-Site Guide, which is largely a work of fiction and certainly not intended as a college text book.

Get your nose into the proper Regs book in your idle moments. Then, anything that you don't understand, you should ask your tutor. Don't be coy about this - after all, that's what your tutor is there for, so you might as well make him earn his money.


Lucia.

 

[riveralt]

You shouln't have to fall back on the On-Site Guide, which is largely a work of fiction and certainly not intended as a college text book.

Evidence please

Please stop insulting my OSG - remember it came out before the 17th edition did

 

[schmeagle]

If your tutor is is moving at such a speed, then it's up to you to tell him to slow down. You shouln't have to fall back on the On-Site Guide, which is largely a work of fiction and certainly not intended as a college text book.

Get your nose into the proper Regs book in your idle moments. Then, anything that you don't understand, you should ask your tutor. Don't be coy about this - after all, that's what your tutor is there for, so you might as well make him earn his money.


Lucia.

Yea thanks for that Lucia.
At the moment I am sleeping with the reg's under my pillow "LOL", the only thing on diversity that I can find is reg 311.1 (for economic and reliable design, the maximum demand of an installation shall be assessed. In determining the maximum demand of an installation or part thereof, diversity may be taken into account).
Unfortunatly this info will not help me in working out the maximum demand and thus I have no choice to return to the OSG. All cable calcs I do are from the regs and getting to know them well now.
The problem is with the tutors is that they are earning there money this year as they have such a large SOW to carry out and that it is up to us to put in the work to stay up to speed? They are really helpfull TBH although I do understand what your saying, I just want to be prepared the next time I am in college and covering this topic so it don't slow down other studend with stupid questions etc?

Thanks pep's you are being helpfull, belive me?
Just wondered if anyone knows an easy way of remembering the calc's etc, sorry

T.

 

[PrinceofDarkness]

OK, Schmeagle. I don't mind thrashing this out with you, however long it takes, so that you have a better understanding of it.

But, you ought to take it in bite-sized pieces - one step at a time: Firstly, understand the difference between Maximum Demand (MD) and Diversity. Then, realise that these two vary from one installation to another (Industrial, Commercial, Domestic etc).

The Regs cover MD generally for all types of installation, but when considering domestic installations, for example, the MD is largely determined by the capacity of the average domestic supply (15 - 18 kW) not in the text book, but in the 'real world'.

The term 'Maximum Demand' is self-explanatory: It's simply the sum of all the individual loads likely to be connected for a simultaneous and significant period.

'Diversity', on the other hand, is a hit-or-miss 'guesstimation' of certain loads which might be on and off for certain insignificant periods (such as cookers with their thermostatic controls). This Diversity factor is sometimes used to give a truer picture of the Maximum Demand of an installation.

Lucia

 

[riveralt]

Just wondered if anyone knows an easy way of remembering the calc's etc, sorry

T.

Practice by putting examples in like I showed you. Just change the oven rating.

If you're at level 3 you really should be able to remember and work out this simple equation.

 

[schmeagle]

yep following you on that lucia, we only doing the domestic/comercial stage at the moment although I would guess that the maximum demand within industrial premises would be easyier to determin as it would be normaly a full load conditions (i.e all machinery running 24 7)?

 

[schmeagle]

Just wondered if anyone knows an easy way of remembering the calc's etc, sorry

T.

Practice by putting examples in like I showed you. Just change the oven rating.

If you're at level 3 you really should be able to remember and work out this simple equation.

Yea working through it now, just keep on doing the layout drawings of imaginary sites then working it out, think I am getting there but it taking some time lol.
Dislexia is not good at this level believe me.
Thanks again.

 

[PrinceofDarkness]

Schmeagle: Let's discuss domestic cooking appliances - and getting back to your O/P about taking off 10A and then adding 10A" (whatever that means?).

The Diversity 'rules' for domestic cooking appliances up to 15KW on a 30/32A circuit, have endured for almost sixty years, and there's been no need to change that 'rule' in recent times.

Why don't you start by reminding me what that 'actual rule' is, just so I know that you're actually in earnest.....

"10 Amps plus ........."


Lucia.

 

[riveralt]

Why don't you start by reminding me what that 'actual rule' is, just so I know that you're actually in earnest.....

"10 Amps plus ........."


Lucia.

Er I already told him at 5.03pm and he working through some examples.

If he is doing C&G 2330 level 3 then he will already have learned dozens of equations - this is one of the easiest ones.

 

[schmeagle]

Schmeagle: Let's discuss domestic cooking appliances - and getting back to your O/P about taking off 10A and then adding 10A" (whatever that means?).

The Diversity 'rules' for domestic cooking appliances up to 15KW on a 30/32A circuit, have endured for almost sixty years, and there's been no need to change that 'rule' in recent times.

Why don't you start by reminding me what that 'actual rule' is, just so I know that you're actually in earnest.....

"10 Amps plus ........."


Lucia.

Well this is the way my tutor goes about it but it just seems long winded?
riveralt's way works too?

Lets say:-
A cooker of 10kW
A hob or 6kW
Ran on the same circuit is a total power of 16,000 Watts.
Divide by the supply voltage = 69.57 Amps

Tutor states:-
You take off 10A = 59.57 Amps
You then take your 59.57 then times that by 30% = 17.87 Amps.
Now you take your 17.87 and add the 10A back on = 28.87Amps
Leaving you using a 32 Amp breaker? (BS60898 - CB).

I guess he correct as it does work but I just get lost lol.
I personally found riveralt's way easyer when found out what he pointing accross? Took me a little while?

 

[schmeagle]

Why don't you start by reminding me what that 'actual rule' is, just so I know that you're actually in earnest.....

"10 Amps plus ........."


Lucia.

Er I already told him at 5.03pm and he working through some examples.

If he is doing C&G 2330 level 3 then he will already have learned dozens of equations - this is one of the easiest ones.

Yea was easier the way you said riveralt, I think I getting the hang of it? Just that I find the Hard principals and reactance easier than this for some reason??? I am an odd ball I know "lol"
Thanks again.

 

[PrinceofDarkness]

Yes, I know you did, Riveralt. But I'm asking him if he has taken that onboard.....


Lucia.

 

[riveralt]

Yea was easier the way you said riveralt, I think I getting the hang of it? Just that I find the Hard principals and reactance easier than this for some reason??? I am an odd ball I know "lol"
Thanks again.

Don't forget that this is part of the process to design a circuit - so you should also be looking at the cable size, length and run (installation method and possible derating). Remember the purpose of an MCB is to protect the cable - so the cable current carrying capacity should always be more than the MCB. For the 16kw example probably 6mm to 10mm don't have my OSG tables to hand.