cooker wiring

[barty74]

hi guys, this is a great forum. everyone seems really helpful.

here is my query, have a new cooker and ceramic hob. i have connected the cooker to a switched fused spur from the ring main and all seems fine.
i have come to wire in the hob, its rated at 6.2kw which is about 25A? the label for wiring it up says to use 2.5mm cable, is this too small? i have a 4mm connection already in place but the cable wont fit into the terminals. could i run a short length of 2.5mm from the connection plate to the hob as the run back to the fuse box is still 4mm?

does that make sense

 

[Steve]

What is the protective device rated at?

 

[barty74]

pardon my ignorance..... do you mean the fuse? if so then its 30A

 

[barty74]

ok, to simplfy......
can i connect a 2.5mm cable from the hob to the terminal plate?

it runs back to the cu on 4mm t and e and a 30amp fuse?

 

[Albert]

The fact that some of the cable is 4mm2 and the other 2.5mm2, does not help you, the carrying capacity of the cable will be seen as of 2.5mm2 (the weakest link).

Where is the 4mm2 coming from, is it from the Consumer Unit to the Hob?
If the answer is yes, it means that this is a Radial circuit and when you are using 2.5mm2 cable you should not use a MCB (fuse) with a value of more than 20A. If you are using 4mm2 you can use 30A/32A , and it seems that the original configuration is OK. Call the manufacturer and ask about changing the connection block in the Hob or any other advice concerning the 4mm2 connection. Good luck

 

[barty74]

thanks albert, i think a call to the manufacturer is in order, i didnt think that 2.5mm would be any good... thats cheap hobs for ya!

 

[Albert]

Just to be fair to the manufacturer, applying diversity will show that 2.5mm2 cable is ok, but I will stick to the 4mm2...

 

[barty74]

ok, sorry to resurect a dead thread, i have used 2.5mm as suggested by the manufacturer and all works. however when all 4 rings are on at max the cable gets warm. it gets really hot under the hob from the rings so maybe its picking up some heat from there too?

 

[Space cat]

You could try something like this:

(Broken link removed)

(Sorry about the long URL but that's exactly how it came off the RS website.)

Rats!!! I've just used the link above to check what I was on about and RS Componenets have scrubbed it. To anybody reading this, it was 2.5 sq mm 3 core mains cable rated up to 85°C and 29 amps. I've deleted the now worthless link because its length was messing up the thread.

 

[plugwash]

It's not ideal but it doesn't seem there is much you can do about it. To be honest given that you aren't likely to have all rings on full very often the cable will probablly last quite a long time (overheating shortens the life of cable but it has to overheat quite before it actually starts melting).

 

[securespark]

You should not be running 2.5 on a 30A fuse!! Change the fuse to 20A.

 

[Albert]

You should not be running 2.5 on a 30A fuse!! Change the fuse to 20A.

Or find a way to use the 4mm2 cable...

 

[Space cat]

I would still be looking for some higher rated 2.5 sq mm cable. When I wrote "RS Components have scrubbed it" I meant the link, not the cable. In any case RS aren't the only shop in town. Type "high temperature cable" into Dogpile.

 

[markymark2406]

What is the load carrying capacity of a 1.5 / 2.5 and 4.00mm?

 

[Albert]

What is the load carrying capacity of a 1.5 / 2.5 and 4.00mm?

Not taking in consideration influences and derating factors for method 1 (clipped direct) T&E cable:
1.5mm2 = 19.5A
2.5mm2 = 27A
4mm2 = 36A