Electric Hob
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Sounds dodgy to me.
I thought it was 27A max with no correction factor.
In addition the circuit goes :
CU -> 32A breaker -> Cooker switch -> CCU (Hob) -> CCU (Oven)
Lamona says 2.5mm for the hob and 1.5mm for the oven.
I reckon the Hob need 4mm and the Oven needs 2.5mm, as with a 32A breaker and CCC of the 1.5mm cable of just 20A that would be a ratio of 1.6 and the max has to be 1.45 doesn't it?
In addition the circuit goes :
CU -> 32A breaker -> Cooker switch -> CCU (Hob) -> CCU (Oven)
Lamona says 2.5mm for the hob and 1.5mm for the oven.
I reckon the Hob need 4mm and the Oven needs 2.5mm, as with a 32A breaker and CCC of the 1.5mm cable of just 20A that would be a ratio of 1.6 and the max has to be 1.45 doesn't it?
It is.
That may be correct but then you have to protect the cable.
You are looking at it the wrong way round. The hob only 'needs' 2.5mm² and the oven 1.5mm².
If you use 2.5mm² a 25A cpd will be the maximum.
For 1.5mm² - 16A (no derating).
If you already have a 32A cpd then you must use 4mm² for both the hob and oven.
No. that's a different matter. You must stick to the actual number.
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Yes - I get your point, but the techical data in their booklet says "Fuse protection 32A" ... and two lines down ... "2.5mm 3 core" - these aren't even compatibale with each other???
EFLI - I'd like your thoughts on how I should proceed here (and any others thoughts please?)
Currently I have :
CU -> 32A breaker -> 6mm all the way to Cooker switch -> to CCU1 -> to CCU2.
As I see it, I can do any of the following :
1. Wire both in 4mm (although it looks like I may be struggling with 4mm on the connection to the oven appliance, so this might not be possible)
2. Wire Hob in 4mm to the first CCU, and then ADD a 13A FCU from the from second CCU so I can then wire in 1.5mm from that FCU to the Oven.
TWO SUBSEQUENT QUESTIONS
A. If I add a FCU, since I can isolate both appliances from the cooker switch IS IT OK TO LOCATE THE FCU BEHIND THE OVEN OR SHOULD IT BE PLACED IN A CABINET?
B. Since the oven will be protected by a 13A fuse, can I use 2.5mm from the seconds CCU to the FCU?[/u]
Mistakes occur.
That would be the best option. 4mm² flex isn't much bigger than 2.5.
No point but yes.
As it's already there I would leave it. As you say, you can isolate it from above.
Replace the second ccu with an fcu. (or socket if oven is pre-wired)
You shouldn't but it doesn't apply (replace second ccu)
You seem to be trying to make more work than is necessary.
Two lengths 4mm² flex - done.
No you must use 4mm² because it is on a 32A mcb.
Forget about the 1.45.
That is the fusing factor of the mcb and not to do with these circuit design calculations.
Forget about the 1.45.
That is the fusing factor of the mcb and not to do with these circuit design calculations.
Ouch - I'm getting a little confused right now, so please help me - can you direct me to the regs about the 4mm cable and 32A, because my initial problem was that the 6.5kW hob yields 28.3A at 230V which is over the CCC of a 2.5mm cable which is 27A (but only just) in normal conditions. I am not talking about the cable from the CU to the CCU (which is already in 6mm), I am talking about the flex cable from the CCU to the appliance.
If what you are saying is right, doesn't that mean the flex of all kettles, toasters etc. plugged into a 32A ring must also be in 4mm, because in fault conditions the current will be way over the CCC of the flex?
Sorry for being stupid, but I am a bit lost ...
Seems like someone else had this query a while back too :
http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=34578
... any more thoughts ???????
http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=34578
... any more thoughts ???????
... and here is another discussion about using 1.5mm on a 30A supply
http://community.screwfix.com/thread/53103
"When an oven shares the same circuit as a separate hob they should be regarded as one cooking appliance just as though it were an orthodox stand-alone cooker. Neither are capable of being overloaded, being as they are, fixed loads. The main consideration here is for short-circuit protection, usually due to the failure of just one of the heating elements. So in that regard, the 1.5mm flex to the oven will be adequately protected by a standard 30/32 Amp MCB.
Anyone unable to understand this principle, should take a look at the internal wiring of an ordinary cooker. It will (typically) have 1/1.5mm HR wiring to its individual elements - oven, grill and four hotplates. It has no need for 6mm internal wiring to match the supply cable and MCB.
Fixed load cookers have always been a special case in the Regulations. With six elements all likely to have an individual short circuit fault at some time, they are notoriously difficult to 'protect'. Added to this are such smaller items as fan motors and lamps which have no internal fuse protection. This is why the main consideration has to be short circuit protection - the load current will look after itself.
Lucia."
So provided that the flex is suitable for the aplliance, 2.5mm for 6.5kw and 1.5mm for 2kw is it OK to wire both onto the same cooker circuit isolated by a single cooker switch protected at the CU by 30A? ... or not
http://community.screwfix.com/thread/53103
"When an oven shares the same circuit as a separate hob they should be regarded as one cooking appliance just as though it were an orthodox stand-alone cooker. Neither are capable of being overloaded, being as they are, fixed loads. The main consideration here is for short-circuit protection, usually due to the failure of just one of the heating elements. So in that regard, the 1.5mm flex to the oven will be adequately protected by a standard 30/32 Amp MCB.
Anyone unable to understand this principle, should take a look at the internal wiring of an ordinary cooker. It will (typically) have 1/1.5mm HR wiring to its individual elements - oven, grill and four hotplates. It has no need for 6mm internal wiring to match the supply cable and MCB.
Fixed load cookers have always been a special case in the Regulations. With six elements all likely to have an individual short circuit fault at some time, they are notoriously difficult to 'protect'. Added to this are such smaller items as fan motors and lamps which have no internal fuse protection. This is why the main consideration has to be short circuit protection - the load current will look after itself.
Lucia."
So provided that the flex is suitable for the aplliance, 2.5mm for 6.5kw and 1.5mm for 2kw is it OK to wire both onto the same cooker circuit isolated by a single cooker switch protected at the CU by 30A? ... or not
No, because there's a fuse in the plug which protects the flex.
Do you feel confident to do the necessary adiabatic calculations to show that flex that size will be adequately protected against faults by a 32A breaker?
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