Hob and Oven - Why would this be ??

[MGFDude]

Hi

Firstly - Hello to you all.
Second - Thanks for all the information that you have all posted here - I have found it very informative (and at times highly amusing... )

Third one ......

I have purchased a replacement hob for the kitchen ( as you would expect!!!) and realised that it would require a 30 amp dedicated supply, due to it having a FLC draw of 5.5kW. No problem I thought as there is already a hob in the kitchen (which was already fitted when we bought the house) and an oven also - which will remain until it also is repaced in a few months.

I started to check the existing set up prior to doing any work and have found an anomaly with the CU and the Oven and Hob switches (and the existing oven and hob connections).
The existing oven is connected to a 32Amp MCB via an isolation switch
The existing hob is connected to a 16Amp MCB, also via an isolation switch.

Now I know that this is wrong but I am just curious as to WHY someone would do this ??
As far as I can tell there is nothing else connected to either circuit (no spurs etc).
I have checked in the oven manufacturers instructions and they recommend connecting via a plug fused at 13Amps.
The manual for the existing hob is missing, but I assume it would require more than a 16Amp supply for FLC ?
The manual for the new hob recommends a 30Amp supply


SO - the crux of my question is this ......
DO I just connect the existing oven to the 16Amp circuit and then use the 32Amp circuit for the new hob ?

Or am I missing something important here ?
Sorry if it is a daft question but the solution seems tooo easy !! And I thought it best to check before I go ahead.
Sorry about the essay but thought I should give as much info as possible

The oven and hob are fitted types BTW

Your thoughts are much appreciated

Many thanks
Regards
MGFDude

 

[RF Lighting]

The only time I can think you would put a 16A supply to a hob is if it was a gas hob and the supply was a spur for the ignitor.

It is possible that someone may have connected to this, and been lucky not to have tripped the MCB.

Do you know what size cable feeds the hob and oven?

 

[MGFDude]

Thanks for the quick reply RF Lighting.

The cables from the CU are (I think ) 6mm2. (for reference the outer sheath is about 16mm across the flat of the cable)
The run is about 2.5M from the CU

I am, as yet, unsure of the cable from the switches onwards as I have not done any work yet - wanted to check the theory 1st

Thanks for your help

Regards
MGFDude

 

[RF Lighting]

It sounds like there is a 30A supply in for the hob, but with the wrong size MCB.

You must ensure that all the cable from the CU right upto the hob is capable of carring the current of the new hob before upgrading the MCB.

Is there an isolator for the hob and one for the oven? If so what do they look like?

Do you have a digital camera to take some photos with so we can see things such as cable sizes, switch ratings, MCB types etc.

 

[MGFDude]

Thanks again

If I understand your reply correctly - - -
The circuit labelled "Hob" is likely a 30A supply (due to cable size ?) but has a 16A MCB fitted ?

The circuit labelled "Oven" is a 30A supply (again due to cable size ?) and has a correct MCB of 32A ?

The cables to the individual isolators are identical
The isolators are separate for each appliance and have a big red switch and a red neon indicator - they look like cooker switches look - but obviously until I open the boxes I am unsure of their rating. I assume they are 45A DP switches - but know how dangerous it is to assume!!! (hence my post)

The CU is a Wylex cat no 804 and the MCBs are B type

My original thought was to just use the existing MCBs and switches - but seeing as my oven only requires 13A I thought it would be better to connect the hob to the 30A supply/MCB and connect the oven to the existing 16A supply/MCB ?

I will try and get a few photos but TBH there is little visible as the cable runs are behind the kitchen backs. I will remove the fridge or something and see what I can see.

Hope this info helps and thanks for your assistance - it is very much appreciated

Regards
MGFDude

 

[securespark]

So you have an 8 way CU with plug in MCB's.

Both circuits in question have the same size cable. But the hob is protected by a 16A MCB and the Oven a 32A?

I suggest someone has inadvertantly swapped them round.

Confirm these things:


cable size,

which breaker kills which circuit,

what the ratings of the two appliances are (look underneath for the hob & inside the door for the oven).

 

[MGFDude]

Hi Securespark - thanks for your reply.

Yes - 8 Way CU with plug in MCBs

Both circuits have the same size cable (arrowed in pic )
Current hob protected by 16A MCB
Current oven protected by 32A MCB

My gut feeling is that someone has inadvertantly swapped them round also !

The correct (and correctly identified and labelled) breaker kills the correct appliance (as above MCBs and switches)

The rating for the oven (which is staying) is not clear as the oven is in situ at the moment - but I can quote from the instruction manual - " This oven must be supplied with a 13Amp switched socket "

The current hob's power rating is unknown - but the new hob is rated at 5.5kW max loading. Which I believe is too much for the 16A circuit/MCB ?
Hence my instinct to swap then over rather than uprate the 16A MCB ?
Am I correct in my thoughts - that this would be safer ?


Many thanks

Regards
MGFDude

 

[securespark]

Having said what I said, I see from the piccy that the correct shield has been used behind each MCB, suggesting it has always been that way. Unless they have been swapped, in which case, the shields have been swapped over too.

I would be happier knowing the rating of the oven. The books have been known to be misleading.

IF:

The oven rating is <16A, then fitting a 16A breaker should be OK, assuming the cable size is sufficient.

The hob cable is able to safely carry 32A, and the switch on that circuit is rated accordingly, then fitting a 32A breaker should be OK.

 

[MGFDude]

I would be happier knowing the rating of the oven. The books have been known to be misleading.

Point taken - thank you
I will be removing the oven to change the hob out - so I will check on the oven for a spec plate.

The labels for hob and oven are little stick on labels
I think that the MCBs and sheilds have always been like that myself - but the house had recently had a kitchen refit before we bought it and I wondered if maybe somebody got the oven and hob swapped over then ?

Here are the switches (sorry about the rubbish picture)
I am not sure of the exact cable size because it is not something I look at often but I will try and get the exact size when I have a bit more room to work with.

Thanks very much for your help

Regards
MGFDude

 

[MGFDude]

what the ratings of the two appliances are (look underneath for the hob & inside the door for the oven).

Doh !

Look inside the oven door - I missed that bit !!

2175 W + fan 40W
240V

is what it says there

Edit: Cable size is a tad more difficult due to access at the moment
I have measured the outer of the cable and crossed checked in the Wiki and it appears to be 6mm2 T+E (13.5mm outer as best I can get in to see the tape).
Is this the correct sizing for a 30A load ?
The runs are about 2.5metres from the CU to the switches /Edit

Apologies
I really appreciate your help

Regards
MGFDude

 

[securespark]

OK. So from the information you have given me, the oven is OK on a plug/socket arrangement via the DP switch & a 16A breaker.

We just need to confirm cable size. How old is the property? If we can ascertain that, there may be an easy way of checking whether the cable can carry 32A or not.

 

[MGFDude]

Hi again
Thanks for your continuing help.

I have checked the wiring - it is 6mm2 T+E all the way to both existing appliances.
The house was built in 1930 and was rewired in approx 1990.

The new hob has a supplied length of flex which is 2.5mm2 - as per the installation instructions (This appliance requires 2.5mm2 cable for a 230V supply)

Would it be better to change the switch front to one with a flex outlet - or is it acceptable to 'go in through the back' (if you pardon my french-lol) with the 6mm supply cable - as per the original fitment.
Just seems to be a good time to fit the correct standard of equipment for the more modern regs?

Cheers
MGFDude

 

[Steve]

Apologies for going OT, but what does that wall-wart TX do below the fusebox, and why does it have a PAT sticker on it?

 

[MGFDude]

Apologies for going OT, but what does that wall-wart TX do below the fusebox, and why does it have a PAT sticker on it?

Hi Crafty

The wall wart is the power supply for my houses osmotic damp proof course. I have no idea why it has a PAT sticker on it. I assumed it was a dated installation type sticker.

HTH

Cheers
MGFDude