Submain cable ideas?

[allybally]

I have a Job to supply a kitchen with power, the board will be 20m from the main head and will be mainly run surface/trunking and under floors (no insulation), I'm thinking of using either 10/16mm2 t&e all will be rcd protected, but my question is...

I have a spool of 6mm2 t&e, could I run a ringmain, so 12mm2 cable supplying the new kitchen board? Just a thought to save some money but not sure if it would be simple thing that would get pulled up in an inspection

Many thanks

Tns system, with no bonding at the kitchen end

 

[Guest55]

yes you can run 2 feeds in parallel so long as theyre the same length , which they will be.

i'd be surprised that just 1 6mm cable wont do the job if its only sockets , lights & appliances , and theres no electric hob.

 

[allybally]

Thanks for the reply, it's a kitchen in a music school, they have a

3kw earn,
a 2.5kw air con / heater
2 x standard kettles
And 3 toasters

So a fairly heavy load ( the kitchen feeds up to 45 people so all is being used for a good hour at least)

 

[i=p/u]

Agree with biff , what's your demand. There's at least 30A available on one 6mm I'd say

 

[i=p/u]

Forget that post. Going what you have

 

[allybally]

So yeah I'd say about 50A total load on the board, and I take it I'm right in saying 1 x 6mm2 cable can take 32A then 2 x 6mm2 cables will be 64A, run reference method A, above ceiling

 

[Fin170]

Are you saying you will be RCDing the cable that feeds the sub main? I'd off that in favour of 6mm or possibly 10mm SWA, 2 core :lol:

 

[Guest55]

Thanks for the reply, it's a kitchen in a music school, they have a

3kw earn, 3000
a 2.5kw air con / heater 2500
2 x standard kettles 4000
And 3 toasters 3000

total 12500 w

12500w / 230v = 54A
i'd apply diversity of around 70% for that lot so

54 x 0.7 = 38A total demand

current capacity of 6mm t&e ref C clipped direct = 47A

check volt drop ; 7.3 mv / A / mtr = 7.3 x 38 x 20 / 1000 = 5.5v drop ( o.k. )


So a fairly heavy load ( the kitchen feeds up to 45 people so all is being used for a good hour at least)

sometimes its best to work it out rather than guess ;-)

 

[allybally]

Yeah I'm going to have the cable supplying the kitchen in a RCD and MCB, then just a main switch with MCB at the CU, I did think about armoured but the rating isn't clear in the regs, and t&e would be easier to run, but I'm open to any help and advice, it's not everyday you get such a large kitchen demand

 

[allybally]

Thanks that's a great post, and diversity on a commercial scale kitchen, can you or should you allow for that? And would you call above ceiling the same as clipped direct? I jut don't want to screw this cable up, many thanks

 

[i=p/u]

40A mcb on 6mm will work zs permitting.

- - - Updated - - -

Your call tho

 

[Guest55]

Thanks that's a great post, and diversity on a commercial scale kitchen, can you or should you allow for that?
i already allowed for that with a generous 0.7 factor.

And would you call above ceiling the same as clipped direct?
yes so long as its not covered in insulation
I jut don't want to screw this cable up, many thanks

..............

 

[allybally]

Thanks very much, and thanks for not patronising me, makes a change

 

[Guest55]

even though ive shown the supply will work with 6mm , i do admit its tight with little room for expansion.
best bet would be 1 x 10mm on a 50a mcb , maybe put 2x 6mm cables in anyway to save hassle from unexpected surprises later.
i just thought id show you through the process ;-)

 

[Engineer54]

Run a 10 mm preferably SWA, or T&E!! At least that will give you some sort of headroom for any future additional appliances like a small oven or 2 ring hot plate and the like!!

 

[allybally]

Thanks for the input, I'm already running a 10mm2 cable for a giants oven they have, and the another cable to This board to supply all the other gadgets they have, does this sound like the best way, and if I was to use 2x6mm2 is this safe to terminate into a main switch, I'm not trying to sound dumb but all I've ever done is the normal tails into switches

Thanks

 

[Guest55]

at 20mtrs long i'd want to use just 1 kitchen submains for everything including the big oven just to save on cable costs and labour time.
obviously this would probably mean a 16mm cable , but i wouldnt use 3 x 6mms , get the right cable to begin with.
is the big oven 3 phase ?

 

[allybally]

No it's only single phase, it's 8kw total electric, the cook is going to use all of the oven when cooking for all her guests, she's just bought this one to replace 2 ovens that were constantly tripping the MCB so she's defiantly hammering the oven! The manufacturer recommends a 40A dedicated circuit, so on this no diversity has been allowed

 

[telectrix]

agree with biff here. run in 2 x 6mm, use 1, keeping 1 in reserve for any future increase in load.

 

[allybally]

I've decided to run a 2 core 16mm2 armoured cable from an isolator to a new CU in the kitchen and take my cooker from there, and there will be enough for the other circuits as well, many thanks for all your advice