Help with diversity

[Markymark981]

[COLOR=rgba(0, 0, 0, 0.701961)]Hi wonder if u could help me [/COLOR][COLOR=rgba(0, 0, 0, 0.701961)]
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[COLOR=rgba(0, 0, 0, 0.701961)]Just rewiring a 3 storey house that's going to be student lets, communal kitchen lounge bathrooms etc[/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]I have worked out the following diversity and demand [/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]Emergency lights 6a x 0.66 = 2.64a[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]Smoke alarm 6a x0.66 = 2.64a[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]4 light circuits 4 x 6a x 0.66 = 10.56a[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]4 ring mains 32a + (3 x 32 x40% = 38.4a) = 70.4a[/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]That all totals 86.24a [/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]Dilemma I have is adding electric cookers and electric radiators [/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]Customer ideally wants 2 stand alone electric cookers but I've worked out each cooker assuming 40a would equal 29.16a if he had 2 it would be 58.32a [/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]Then he wants 500w convector heaters either 7 or 15 of them spilt over 3 floors in total 15 would bring 7kw and need to be on a 32a fuse and if he went for 7 it would be 3.5kw and need a 16a fuse, apply diversity and that would add 21a or 13a[/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]Questions I have are[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]1. if he had the electric rads could I put 3 radial circuits into one 32a fuse [/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]2. As it stands without cookers or rads it's would be[/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]86.24a[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]115a with one cooker[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]144a with 2 cookers[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]157a with 2 cookers and 7 rads[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)]165a with 2 cookers and 15 rads[/COLOR]
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[COLOR=rgba(0, 0, 0, 0.701961)]Which would be acceptable, my old old lecturer stated if it exceeds 100a it'll just blow main fuse so don't worry

Also found someone using the add up all themcb values and times by .40 anyone else used this or know if it's ok?

cheers

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[Markymark981]

Ok thanks am I missing something with ththe smoke alarms been on a 6a fuse?

 

[davesparks]

Ok thanks am I missing something with ththe smoke alarms been on a 6a fuse?

Yes, you've missed a fundamental bit of the science of electricity, the load will only draw the current it requires, it will not have a current equal to the OCPD rating forced through it. Ie a 1A load supplied by a 6A mcb will only use 1A!
A few smoke alarms will draw 9/10ths of bugger all current and can be ignored when assessing the max demand.
Likewise your lighting circuits won't really be loaded to 1.2KW each will they? Especially not a circuit which is exclusively emergency lights.
Which raises the interesting question of why the emergency lights will be on a seperate circuit to the normal lights?

 

[Markymark981]

Thanks dave emergency light it's just how the customer wanted them on the cu...trying to disway him from the electric rads but only issue I'm coming across is he's mate has the same type house converted like he's and he has them so while I'm trying my best to explain and change his opinion I also don't want to look stupid if they get another spark into install it

And I'm worried that any bigger rads is going to increase they already large demand on the installation, hes told me to install even tho it's way over (rads and cookers) and said he would sign a disclaimer but don't know where I would stand as I'm installing demand larger than the 100a max

 

[Markymark981]

An old lecturer told me don't worry too much as at worst it'll just blow the main fuse but I'm not entirely comfortable with that response

 

[Markymark981]

Can't seem to find a proper answer in any of the onsite guides

 

[Markymark981]

And never had an issue before as the bulk of rewires have been way under 100a

 

[davesparks]

If it has the correct size heaters then a greater diversity factor will come in to play as the thermostats will cycle correctly.

As for the emergency lights, is the customer suitably qualified to make that decision? Do you understand why putting them on a seperate circuit may be a bad idea which you, as the installer, could be liable for?

Have you ever carried out a load study on a domestic property? Or even measured instantaneous current draw with a clamp meter?

 

[DPG]

An old lecturer told me don't worry too much as at worst it'll just blow the main fuse but I'm not entirely comfortable with that response

Great advice that. 'Don't worry if demand is a bit too high, it will just knock out the entire system and need the DNO to come and fix it'. Makes you wonder why we bother working max demand out really. Daz

 

[Markymark981]

As for the emergency lights, is the customer suitably qualified to make that decision? Do you understand why putting them on a seperate circuit may be a bad idea which you, as the installer, could be liable for?

Hi dave this is the first time I have been asked for emergency lighting I've checked onsite guides and it didn't mention anything about them been on either a separate circuit or the lighting circuit, I just did it on a separate circuit for identification on the cu

would I be ok to connect the emergency lighting into the same mcb as the downstairs lights if they don't pull much power?

sorry to ask so many questions but these two topics (emergency light and demand) I've not had issues with in the past

cheers mark

 

[Markymark981]

Great advice that. 'Don't worry if demand is a bit too high, it will just knock out the entire system and need the DNO to come and fix it'. Makes you wonder why we bother working max demand out really. Daz

i know daz and I'm finding it difficult to find the answers I need

 

[Andy78]

Hi dave this is the first time I have been asked for emergency lighting I've checked onsite guides and it didn't mention anything about them been on either a separate circuit or the lighting circuit, I just did it on a separate circuit for identification on the cu

would I be ok to connect the emergency lighting into the same mcb as the downstairs lights if they don't pull much power?

sorry to ask so many questions but these two topics (emergency light and demand) I've not had issues with in the past

cheers mark

Think about it. Emergency lighting is there to be activated and provide lighting when the main lighting fails.

 

[DPG]

Hi dave this is the first time I have been asked for emergency lighting I've checked onsite guides and it didn't mention anything about them been on either a separate circuit or the lighting circuit, I just did it on a separate circuit for identification on the cu

would I be ok to connect the emergency lighting into the same mcb as the downstairs lights if they don't pull much power?

sorry to ask so many questions but these two topics (emergency light and demand) I've not had issues with in the past

cheers mark

But how does the emergency lighting know to come on? Daz

 

[DPG]

Sorry Andy, your post wasn't there when I typed Daz

 

[Markymark981]

Think about it. Emergency lighting is there to be activated and provide lighting when the main lighting fails.

i understand but each floors as its own circuit and the hall and landings have their own circuit so could I join the hallways and emergency lighting feeds into the same mcb save me having to go back and re wire?

 

[Andy78]

i understand but each floors as its own circuit and the hall and landings have their own circuit so could I join the hallways and emergency lighting feeds into the same mcb save me having to go back and re wire?

As designer and installer, how you achieve the requirements for emergency lighting is up to you.