another max demand question

[Mr Mark Sparks]

hi all
i am in the process of wiring a 1 bed annex at the bottom of a chaps garden
the house was on a 63amp supply and its been upgraded to 100a
the loadings in the annex are
6kw electric boiler
8 kw shower (the shower is to be fed through a contactor which takes priority over the boiler so the boiler goes off when the shower comes on)
an 8kw oven/hob
2 rings 1 with a 3kw water heater on
the other just 6 twin sockets in lounge and bedroom
so minimal load
another 3kw water heater
2 lighting circuits 10 x 11w low energy fittings on each

what do you think max demand will be i want to fuse down my submain as low as poss

cheers mark

 

[Mr Mark Sparks]

hello?? anybody there!!

 

[Guest123]

Without doing any sums I'd say a 63A sub would be the minimum.

Possibly get away with a 50A one depending on use i.e who's going to be living in it....one little old dear or a small family???

 

[Sparky Ninja]

hi all
i am in the process of wiring a 1 bed annex at the bottom of a chaps garden
the house was on a 63amp supply and its been upgraded to 100a
the loadings in the annex are
6kw electric boiler
8 kw shower (the shower is to be fed through a contactor which takes priority over the boiler so the boiler goes off when the shower comes on)
an 8kw oven/hob
2 rings 1 with a 3kw water heater on
the other just 6 twin sockets in lounge and bedroom
so minimal load
another 3kw water heater
2 lighting circuits 10 x 11w low energy fittings on each

what do you think max demand will be i want to fuse down my submain as low as poss

cheers mark

Off the top of my head..

I'd need to work out the current demand of the cooker. So knowing if there is a socket on the plate would be of benefit to me, I am going to assume it is not.
I take the first 10A of the rated current plus 30% of the remainder.
Therefore..

I = 10 + (30% of (34.8 - 10))
I = 10 + (30% of 24.8)
I = 10 + 7.44
I = 17.44A Current demand of cooker (except x-mas day )

Therefore... applying diversity...

Domestic -
100% current demand of the largest circuit +40% of current demand of every other circuit.

So.. I will consider the cooker the largest circuit due to it being initially 8kW, therefore put aside 100% of it's current demand (17.44A)

I'll omit the 6kW boiler, and stick with the 8kW shower

Remaining we have..

8kW = 34.8A - Shower
32A - Ring 1
32A - Ring 2
(10 x 11w = 110w) = 0.48A - Lights 1
(10 x 11w = 110w) = 0.48A - Lights 2

Total remaining = 99.76A

40% of 99.76A = 39.9A

Therefore, 39.9A + (100% of largest circuit) 17.44Amps = 57.34Amps


So I work it out as - 57.34 Amps


FYI - If current demand of the cooker isn't considered and is kept 8kW, It equates to 74.7Amps.

 

[Mr Mark Sparks]

widdler thats right no socket on the cooker
i see you have missed off the water heater but i may feed that off the small ring anyway

lenny use at the most will be an oap member of the family

i am just worried if i give the annex 63a that only leaves 37a for the house i would/may try 50/50 first and see i can rig something so only shower also takes priority over oven as well as boiler so only 1 large appliance will be on at a time not worried about oven and boiler as oven wont be fully loaded

maybe a 2 possition switch any other ideas

 

[Sparky Ninja]

I assumed both 3kW water heaters were on each ring, it would help with your demand if they were.

 

[Sparky Ninja]

I am just worried if i give the annex 63a that only leaves 37a for the house i would/may try 50/50 first and see i can rig something so only shower also takes priority over oven as well as boiler so only 1 large appliance will be on at a time not worried about oven and boiler as oven wont be fully loaded

maybe a 2 possition switch any other ideas

How is the whole installation being utilized?