Extension Supply

[kernow]

Hi

I have extension to supply. Extension is kitchen / diner downstairs. Bedroom / bathroom upsatirs.

Using oil combi for shower

Using gas for hob.

Rest of house wiring a muddle dont want to touch so want to run a new supply off exisitng wylex split rcd board to  second small cu.

Length of cable from cu 1  to cu 2 is 32m

cliped direct

So calculations in extension are

ring - 32 amps

cooker (oven) 4.35 amps

lighting 5.22 amps - 12 lamps all together using the 100 watt rule but in theory they are led.

estimated demand 39.8 amps

distance 32m

use 3% for lighting

voltdrop 5.6 volts

max cable length 39.4 m

current capacity of cable  65 amps

therefore 10mm is fine.

10mm t and e from cu 1 to cu 2.

In cu 1 use a 40 amp rcbo as i cant get the cable more than 50mm from surface.

in cu 2 one 32 amp mcb for 1 ring sockets

one 6 amp mcb for 1 radial lights

oven will be fed from ring  (1kw) via double pole fcu.

not ideal having lights and ring on same rcbo but if fault at least rest of house will have light - sockets.  could split it into 2 rings for sockets and 2 radials for lights but seems overkill for 3 rooms?

 

[steptoe]

if your clipped direct why the 30mA RCBO ?

 

[kernow]

Yes my mistake -

Ref Method C. - mostly clipped direct but some plastered in oval therefore < 50mm this is why rcbo

 

[Sharpend]

A 1kw oven? Seems a little small?

At which point does the cable go below surface?

When you say split rcd, that's a dual rcd board with or without any unprotected ways?

 

[Zeespark]

Why bother coming off of the existing CU? split the supply by Henley block then there are no issues with the old wiring. As well as that, why not use the actual wattage values of the LED lights rather than the 100 watt rule, which, thanks to the EU, no longer really exists due to the downgrading of sizes to 60 watt?. It is also very unlikely that you would actually use a full 32A load on your sockets, downgrade your forecasts to 20-25A would be My advice.

Is the extension feed being run indoors or outdoors? if indoors, I would liekly run it in either twin and earth or hituff.

Andy Guinness

 

[NozSpark]

I just had that with my inspector

He sees the db and says 28 lights!

My response was that they were nearly all LED and the rest are CFL..

His response was "that's OK then"

 

[kernow]

A 1kw oven? Seems a little small?

Hi oven not cooker - most ovens seem to be between 750 watss and 2 kw that i see these days and most have a plug on

downgrade your forecasts to 20-25A would be My advice.

yes this makes sense but following the guide it was where it states 100w per lamp fitting and diversity states 100% of first ring and as this is 32 amp. You bring common sense into the equation . yes henley blocks is a good idea. thanks

 

[SPECIAL LOCATION]

yes this makes sense but following the guide it was where it states 100w per lamp fitting and diversity states 100% of first ring and as this is 32 amp. You bring common sense into the equation . yes henley blocks is a good idea. thanks

NO..  diversity does not state anything of the sort...

Read second paragraph of appendix A page 109 OSG....

Don't just jump straight to the example tables over the page...

The tables offer some suggestions as to how you may want to calculate your loads & thus diversity..

But as per page 109...

It is IMPOSSIBLE to specify appropriate allowances...

& installation designer may increase OR decrease values accordingly!!

Too many people treat the regs and OSG as a set of rules..

whereas they are a set of guidance which can be amended as appropriate to a specific installation!!

opcorn

 

[Blue Duck]

Where's the scoob button?

 

[Amlec]

I usually allow 1 amp per double socket, which takes diversity into account. If installing only one ring main, realistically its never going to be loaded to 32 amps.

 

[Andy™]

so a kitchen with 6 double sockets will be fine on a 6a MCB?

 

[Blue Duck]

How many appliances can you think of that use nearly 3000w?

 

[steptoe]

Kettle

Toaster

Dishwasher

Washing machine

Iron

Hairdryer

Oven (OK its only 2.8 but close )

Is it a competition,?

 

[Badger]

How many appliances can you think of that use nearly 3000w?

badgers christmas lights :slap :slap :innocent ] ]

immersion heater

water heater

 

[Blue Duck]

Was a response to the suggestion that 1 amp per socket

Steps there's a bottle of jamersons in my van you have that if you like & badger you getting 3 phase put in this year?

 

[kerching]

Tumble dryer

Big HD waste disposal unit

Under floor heating

Outside patio heater

Arc welder

Compressor

Plasma cutter

Bench saw

Denford Viceroy lathe

All of above in my garage

Just saying

 

[Blue Duck]

Arc welder

Compressor

Plasma cutter

Bench saw

Denford Viceroy lathe

Just saying

:slap

Thought they were in your kitchen

Not sure where this 1a per socket thing came from? You add 5a for a socket on a cooker plate which usually has a kettle plugged in to it & occasionally I do find the whole house plugged in to the cooker point :|

 

[kerching]

:slap

Thought they were in your kitchen

Not sure where this 1a per socket thing came from? You add 5a for a socket on a cooker plate which usually has a kettle plugged in to it & occasionally I do find the whole house plugged in to the cooker point :|

Well of you saw some of the sh'ite that the wife turns out under the broad church of FOOD.......you would realise how close to the bitter, tasteless, undercooked, overcooked ,i inedible truth you actually are.

.....yes, i do most of the cooking!

She has just shouted "buzzer kerch" ....so the chicken parcels with home grown chillis, basil and oregano accompanied by home grown roast potatoes with rosemary, garlic and peppers are ready.

She will pour the wine, she knows her place

Just going to eat

 

[Manator]

NO..  diversity does not state anything of the sort...

Read second paragraph of appendix A page 109 OSG....

Don't just jump straight to the example tables over the page...

The tables offer some suggestions as to how you may want to calculate your loads & thus diversity..

But as per page 109...

It is IMPOSSIBLE to specify appropriate allowances...

& installation designer may increase OR decrease values accordingly!!

Too many people treat the regs and OSG as a set of rules..

whereas they are a set of guidance which can be amended as appropriate to a specific installation!!

opcorn

This is why I design electrical installations. Its so much easier than following a guide. However you do need to know your calculations back to front, and the subtle differences in designated mcb/rcbo types.