another hob question

[speccy]

I have read through the hob posts!

Okay i have my 6mm feed to leccy hob. So then for safety i want a dual pole isolating switch on the wall to the right of hob.

Is this right:

Run 6mm down wall to worktop level to dual pole 40amp (?) switch, run2.5mm out down to hob level, break out wall with surface flex out junc box.

Trying to find MK square dual pole 40 amp, do they make one?

 

[breezer]

why the change from 6mm to 2.5?

 

[speccy]

well i guess the cable from dual pole switch to cooker junc box is less than a metre, save messing about with 6mm cable or is it still necessary even on a short run like that?

 

[andy]

well i guess the cable from dual pole switch to cooker junc box is less than a metre, save messing about with 6mm cable or is it still necessary even on a short run like that?

to do that youll have to have a 20A MCB. use the same cable thruout.

and since you think you can use 2.5 instead of 6 implies you have no idea WTF you are doing

 

[speccy]

Andrew, there's no need to be like that, i support people on mechanical, pc forums, walk into my world and im sure you'd have no idea either.

Although my advice is normally technical and of a non life threatening nature, when people need correcting i correct them without the need to tell them how thick they are. We all have our bad days though.

I've come here to ensure i learn how to do this properly and safely. If you don't wanna help then keep your comments to yourself.

Thanks.

 

[mapj1]

Depends on the rating - if its an oven, then 2.5mm (20A feed) may well be enough, as these are usually only 10-15 A However, a 'hob' may imply high wattage rings - so please look at the rating plate, and then we can tell you the cable size. You may need all of the 6mm cable.

Even on a 40A breaker thinner cable is OK but only if the maximum load is limited, and if the cable is short enough to preserve short circuit protection
''''
-The device protecting against overload may be positioned on the load side of (downstream from) the point of reduction, provided that the unprotected cable length does not exceed 3 m, that fault current is unlikely, and that the cable is not in a position that is hazardous from the point of view of ignition of its surroundings.
''''
This Regulation is useful when designing switchboards, where a short length of cable protected by conduit or trunking feeds a low-current switch fuse from a high current fuse and allows 0.5mm flex on 13A fuses, providing the applience has an internal fuse, and meter tails to storage heater CUs rated for the load, rather than the company fuse. Must say I always feel happier with a fuse and cable rating in step though, even in the rare cases where not esential.

Now please tell us the rating of your hob (and if it has an internal fuse)!

 

[speccy]

Many thanks MAP i see what you're saying.

Well..u see whilst i fit my kitchen i thought id ad provision for an electric hob, always fancied a half induction/gas hob.
BUT for the moment im going with gas.

Assuming a hob uses say er 8kw with all burners on (guesstimate) that will of course exceed 32amp. So sorry i cannot supply specifics but i would of course ebb towards the safest method.

The last electric hob i pulled out no way looked like it was using 6mm cable! Which is why i assumed it was ok to use a short 2.5mm loop from dual pole to junction.

 

[andy]

after diversity (10A + 30% of rest of load), you may be able to use a 2.5mm cable, since its unlikely youll have everything burning at the same time, however, if you do use 2.5 and keep the MCB/fuse at the higher rating (say 40A) and you do use more power, the 2.5mm will overheat and potentially cause a fire and the MCB wont trip to protect the cable since you use a thinner cable

and since you say its a very short run, do it with 6mm

 

[speccy]

K will do, many thanks Andrew.

 

[ban-all-sheds]

after diversity (10A + 30% of rest of load), you may be able to use a 2.5mm cable

Does diversity apply to the selection of the cable, or to the assumption of demand when calculating maximum demand for an installation?

 

[andy]

after diversity (10A + 30% of rest of load), you may be able to use a 2.5mm cable

Does diversity apply to the selection of the cable, or to the assumption of demand when calculating maximum demand for an installation?

not sure. altho i think the diversity of the cooker should be higher (mayb 80% load) because at some point (large party for example) you may have everything on. then the fuse trips every 2 mins....

 

[sparkybird]

Fresh from my college course - the diversity is applied to the appliance demand (design current), which will of course affect the cable size later on in your calculations

SB

PS Did I pass?