hob /oven install

[davecc]

hi after doing some research i think i might have a problem.

just about to dot n dab walls in kitchen extension on checking cables me thinks guy who did electrics has fitted 4mm twin&earth approx 12m run maybe just more. 40Amcb in new consumer unit

kitchen from howdens so own brand electrics (lamona) dimplex

hob total power 6000w. 2x1800w,2x1200w me thinks this equates to 25A max ?

double oven/grill maximum combination load 4965w. fan25w, light25w, ovenstirfan38w, mainoven2300w, top oven1325w, dualgrill 1655w/2575w. me thinks this equates 20.6A?

45AMAX LOAD
both rated at 230v/50hz

was going to fit 45a double pole control unit then split with 6mm to two 45a connection units one for oven and one for hob less than 2m
advice appreciated and diagrams are welcome

 

[baldsparkies]

Yes I would say you do have a situation to sort, and a customer who may need an explanation as to why. If indeed you have a 4mm supply cable, then the hob oven combination is a no go, especially with regards to a 40a mcb. You are going to need a 6mm radial back to the board. If it were me I would leave the 4mm in situ, downrate the mcb and have the hob and double oven on seperate circuits. As said no point taking the 4mm out now its there.
Put the Hob on the 6mm 32a mcb. and the oven on the 4mm 20a. But thats just me others may come up with alternatives.

 

[Des 56]

Read pages 107 and 134 of the on site guide,it will along with installation method,allow you to calculate the likely load, which is needed to check the cable current carrying capacity of the installed cable and the choice of opd

If these calculate satisfactory,why are you increasing cable size to hob greater than the supply cable,also the 6mm to the oven is also overcooking (forgive the pun) what may be required

The 4mm could be rated as high as 37 amps or as low as 17.5
The mcb could become 32 amp
The likely load may be 28 amp

you will need to calculate to decide ok or no
Check also voltage drop

Before boarding it out I would also do as advised by baldsparkies and eliminate any doubts
4mm is not the usual install size for these items

 

[electric-ian]

Yep, I'm with baldsparkies on that one.

4mm definitely no good for both..

 

[Amp David]

Why if you are doing the dot and dab are you doing the cable calcs for the spark? Is this some kind of coyboy initiative?

 

[davecc]

thanks for replys ,
first its my kitchen and i apologise if ive misinformed i am not an electrician,
i had an extesion built shell n roof with intent to do all internal work floors ceilings boarding partitions etc along with fartherin law joiner/builder electrician is coming back at later date to sign off test etc,
i was going to put boxes in for connection units and drop cables in to control box so could carry on boarding.
the reason why i was going to use 6mm there was no 4mm at b+q or wickes this was at 5pm saturday i didnt know that 4mm was installed till on return this was gunna be my sunday job.
running new 6mm in nightmare as ceilings boarded no access from above single storey with 3.6 catnic running lenth of opening but if its got to be done!
only other thing is theres a double socket ring circuit next to control unit can a spur be taken n feed either hob or oven
may be a silly question but ??
hob recomends 3x2.5mm (ho5rrf 3g 2.5) or equiv,

 

[Jason Smith]

Mate, its problems all the way- People buy new cookers all the time and dont give a thought to the new bigger loads on the old cables. Some may of course be ok, I ALWAYS install 10 mill to cookers, its a bugger to get in the cooker sockets but in is in. Get that wire out, and a ten mil in. Sleep safe at night. Question for everybody though, if the return leg on a ring main, 2.5, going obviously back to the same MCB gives us a CSA of 5 mil, and 32 amps MCB, then could we return the 4 mil to the same mcb giving 8 mil csa ? can of worms I would like to open lol -.

 

[davecc]

well since project has stood still for a year due to nervous breakdown im just tackling little bits now +then and been off work a year.
i did come here for advice the right forum !!
not diy joeys home page where little boys in sandpits play and full off egostistic aholes!!
oh n thanks for remarks and future remarks AMP DAVE IF THE HAT FITS.

 

[Amp David]

Bless Him.

It fits nicely

 

[baldsparkies]

The advice given in earlier posts stands good,
Now the situation has been fully explained you need to consider the regulations regarding building control.
The law,as it stands, requires special location electrical work to be signed off under part P of your local building control authority.
The (Kitchen is one such area) For that reason the work you describe should not be undertaken as a diy project. If you are in any doubt please consult a qualified electrician who is registered with a competant persons scheme, ie
NICEIC, ELECSA, NAPPIT. Or you can have the work examined by a building inspector prior to boarding, but they would charge in the region of £150-00 for such work.
Also these circuits have to be fed as independant radials from the consumer unit, coming off the ring is a definate NO NO.
Hope you find this post helpfull.

 

[davecc]

thanks baldsparkies,
when building inspector last came to check off catnics and box and concrete lintels. Said he was happy with what he saw regards all sighting of electrics heights cable runs capping etc and said could go ahead and get on with boarding,
so can i myself put in 6mm cable and NOT connecting at any ends just so its there even take pictures etc,
cheers dave

 

[baldsparkies]

Can't see a problem with that, with both your 6mm and 4mm cable runs you have more than adequate scope for the hob and oven loads. Just put them on seperate breakers at the board and your good to go. Electrician or LABC permmiting of course. Remember I am not on site, so have a competant sparky check things over and your good to go. Take care and good luck with the works.

 

[davecc]

hi baldsparky n co,

think i got it wrong think 6mm cable installed origianilly (18mnth ago) stripped back some new 6mm and cant tell the difference ?

so back to original post is 6mm ok,
or should i drop another 6mm in while i have chance? ie two 6mm radials
oven 20amax
hob 25amax

 

[Notsosmart]

Definitely run in an extra circuit with 6mm & double check with the Electrician what he ran in (as thickness of insulation can vary). 18 months may be a long time to remember but if I was asked the question I would know as I only run 6mm as standard for cooker switches.

 

[Guest123]

or should i drop another 6mm in while i have chance? ie two 6mm radials

You know it makes sense.

 

[baldsparkies]

As others have said. But to the reasoning behind this. Volt drop to the oven and hob can reduce the efficiency of the appliances and increase cooking times in practical terms. Ever wondered why the christmas turkey seems to take longer to cook on christmas day? Nope its not your immagination its down to lower voltages from the national grid, cus everyone is doing the same thing. So its definately to your advantage to fit that second supply. There are also thermal effects to consider, and that down to the installation method and the ability for the cable to disperse heat over the run will also be covered.

 

[davecc]

to those that replied with thought i thank you .

i have just cut hole in ceiling and drilled through cavity wall and pushed through 3m pole so can pull new cable through tommorow after a visit to CEF .
does make sense to do it now.
but sense is not easily seen to a tired mind,nor is an easy decision decided.
thanx, dave

and AMP DAVE may you have one amp to many.............

 

[Jason Smith]

He may of had one amp to many but one amp to many will also set fire to yer house mate !