Hep with demand and 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 but I am as already going to have to get him to upgrade it he 80a main fuse to a 100a


oh and I have just found someone using the add up all the mcb values and times by .40 anyone else used this?[/COLOR]

 

[Darkwood]

Think we need to ask a mod to clear your thread up... its full of programing values and settings..

 

[HappyHippyDad]

Hi Mark.
Without trying to decipher the message too much I would say:

Work out the max demand for the lights/smokes and other items with a known power output based on there total wattage rather than the MCB.. and then apply diversity.

Also, I dont think it is a good idea to just think that it will have a 100A fuse so if it takes more than that it will 'just blow'. A 100A fuse will never blow with 100A flowing through it, will take at least 30minutes to blow with 200A flowing through it and perhaps days/weeks/months (or never) with 115A - 165A flowing through it. So it would be a poor design and dangerous especially if the tails are 16mm .. are they?

Saying that.. I doubt your actual demand will be anywhere near that high in reality.

As for the x0.4, I do see that banded around alot. I think it is from a particular DNO but cant be sure. I expect it is accurate 95% of the time, but I have always felt like it's cheating a bit because you just want to make the figures fit rather than give them proper consideration! I still used it once though!

 

[davesparks]

The x0.4 comes from that wonderful work of utter nonsense called bs7671, or one of its helpful picture book guides.