Derating For Grouping - Real World

[gembrain]

Hi,

My slowest refurb in history continues.

Sparky has run all the cables, replaced the CU, and wired some of the circuits so we have power where needed. I'm now doing dogsbody of clipping all the cables before the ceilings go up.

Being probably overkeen on avoiding any nuisance tripping I asked for loads of circuits all with individual RCBOs and the relevant ones are below. Kitchen wiring not relevant as it has its own route from the CU to kitchen area.

32A RING Ring - Utility Room U 2.5mm

32A RING Upstairs Sockets U 2,5mm

32A RING Office U 2.5mm

20A RADIAL Immersion and Shower Pump U 2.5mm

6A RADIAL External Lighting U 1.5mm

6A RADIAL Upstairs Lighting U 1.5mm

6A RADIAL Downstairs Lighting U 1.5mm

6A RADIAL LED Strip lighting and Misc U 1.5mm

6A RADIAL Smoke Detectors and Alarm U 1.5mm

6A RADIAL *C CURVE PLEASE* U 1.5mm

32A RING Downstairs Sockets UD 2.5mm

20A RADIAL External Sockets UD 2.5mm

20A RADIAL A/V Sockets UD 2.5mm

In normal use none of these circuits are going to be used at anything like full capacity (or even 30%) but as they go through a hole in the wall from the CU and up the wall to the ceiling if I do a calc for derating for grouping then I get a fairly horrendous figure. Quite a few go through 50mm sound insulation so as I understand it that knocks me down 12%.

Theoretically if the gas heating failed mid winter then there would be the immersion and a few 3Kw heaters blowing everywhere which would obviously load some of the cables at over the 30% exclusion level.

Sparky says don't worry about it (but then he says he's never bothered about it?) so I thought I would double check.

Please not too many flames about should have thought of all this before! 

I'm not perfect (as the wife will testify quite often) I just like getting it right.....

 

[binky]

it's a house? DNO allows 16A per house, cos that's what its actually likely to use apart from a few 'spikes'. The more circuits you put in (which is good practice) the worse the figures get. I gave up on diversity calcs for this very reason years ago.

 

[gembrain]

Yes - a basic 4 bed house...

Average over 2014 at 3.6amps....

Will go up a bit when the wife gets a kitchen

 

[Evans Electric]

Its a   4 bed house ..................and you've put in ..what ....7  power circuits ...   Without the kitchen ....Jeez!

I'd forget all that derating if I were you .  The circuits will be running at 5% of their capacity.

 

[Badger]

well i put the following in our house and its only 2 bed

up sockets

internet/computer sockets

cctv

alarm

study lights

up and loft lights

outside lights

shed/greenhouse

pond

down sockets

outside front socket

outside side socket

kitchen sockets

bathroom heater rail

down lights

bathroom lights

boiler

cooker

shower

garage sockets

security lights

 

[gembrain]

You serious Badger?

If so I don't feel so bad

 

[Sharpend]

Were you bored that week badger?

 

[Badger]

im deadly serious yes!

and it means not all the wiring is being used at full power, shower wired in 10 mm as per and cooker in 6mm as per.

 

[Andy™]

well i put the following in our house and its only 2 bed

up sockets

internet/computer sockets

cctv

alarm

study lights

up and loft lights

outside lights

shed/greenhouse

pond

down sockets

outside front socket

outside side socket

kitchen sockets

bathroom heater rail

down lights

bathroom lights

boiler

cooker

shower

garage sockets

security lights

surely you could have put the shed and greenhouse on their own circuits instead of making them share

 

[Badger]

surely you could have put the shed and greenhouse on their own circuits instead of making them share

no i cheated used the same 6mm armoured under the patio and resin 'y' jointed one each leg to greenhouse c/u and other leg to shed.

 

[Evans Electric]

I was thinking of putting every light fitting on it's own circuit   or maybe a sub-main to every room with a 2 way CU  but I soon got over it .   :innocent

 

[binky]

no i cheated used the same 6mm armoured under the patio and resin 'y' jointed one each leg to greenhouse c/u and other leg to shed.

no one can resist a small bodge :slap

only joking

 

[Badger]

I was thinking of putting every light fitting on it's own circuit   or maybe a sub-main to every room with a 2 way CU  but I soon got over it .   :innocent

the thing with having more lighting circuits is when a fault happens you can still see through the property when the mcb trips out or in my case rcbo

 

[Andy™]

what if there is a power cut?

then again, you probably have a UPS & backup generator capable of powering all the lights & xmas lights

 

[gembrain]

Well I've got the UPS for my important stuff - my computers

If the wife wants to watch Corrie during the power cut there's always the exercise bike with a dyno.... 

On the derating question does anybody object to me following Evans and Binky and ignoring the specific derating calcs - as long as I use a bit of common and don't go tying bunches of cables together that might be used in a no gas heating situation?

 

[Andy™]

On the derating question does anybody object to me following Evans and Binky and ignoring the specific derating calcs -

nope

 

[binky]

use advice with caution :^O

 

[Badger]

what if there is a power cut?

then again, you probably have a UPS & backup generator capable of powering all the lights & xmas lights

i have actually put a change over switch and genny hook up in aswell