Seperate Oven & Hob (Confusion)

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Hi All,

I currently have a radial circuit with 6mm cable & a 32amp mcb. I need to run a separate oven (3kw) & hob (6,270w). Not sure if i need a new mcb with higher rating or 10mm cable or both.

I understand i will need double pole isolation switch. Then a fused spur off the cable to run the oven. Then the hob will run from the cooker control unit further along the cable.

Please Advise, Thanks in advance.

CL :confused:
 
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anything more than a 32 is pushing it i belive 40A is ok in normal domestic situations but i'm not sure

i'd keep the current 6mm cuircuit with it's current breaker for the hob alone

and either put the oven on the ring or run in a dedicated 16A 2.5mm cuircuit for it (depending on how heavilly loaded your kitchen ring is already) terminateing in either a socket or fcu
 
Thanks Plugwash.

The problem i have is that i live in a flat with galvanised steel conduit and no easy access to the ring main (sockets).

If i can do it all from the exisiting socket configuration i'm laughing but i think i am going to have to open the wallet, again!

B****y f*****g flat!
 
if there is no easy access to the ring a dedicated cuircuit back to the CU for the oven is probablly your best bet
 
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You are allowed, with a cooker, to work out its consumption using the formula 10A + 30% of the remainder. In your case that would come to 19A, and you've got 32 to play with.

It's not a method I agree with when designing a circuit, as it does assume that you will never turn everything on at once, but it is allowed, and it would not be dangerous, given the 32A breaker.

As you've got some difficulty in putting in a circuit rated at the full 40A the cooker could draw, why not use what you've got for a while, and see if you do get any problems in practice?
 
I would also point out that these are two seperate pieces of fixed equipment and as such should be on their own circuits.

The Hob should definitly be on a circuit of it's own due to it's rating. The oven can go onto a radial circuit or even a fused spur off the ring..own circuit is far better though.

Should you choose to run the two off the one circuit, I would strongly urge you to run the oven via a fused spur on the cooker circuit.
 
Another example of the illogical nature of many of the wiring regulations.

Putting aside the arguments over the "10A + 30%" rule, if this identical oven and hob were manufactured as one appliance, with one set of connections, then it'd be perfectly OK to put it on that 6mm/32A circuit.

But split the two up, and they are supposed to be on two circuits, even though it would be utterly impossible for the load on the cable to be any higher with the two deconstructed items than a combined one. In fact, you could argue that with them separated, you reduce the length of the cable which is exposed to the full current.
 
Ban, to take your comments to task..sorry fella..

If the two items were ONE appliance, then the total load would be some 10kW / 230V = 43.47A, so a single 6mm 32A circuit would not be sufficient to supply it.

The circuit should be in 10mm and on a 40 or 45A MCB. Whilst, as I have said on numerous occasions, diversity should not be applied to circuits for cookers (IMHO), I think we can assume that is will normally only be used at about 80% FL, or about 35A, so a 40A MCB would suffice in this instance.

As 6mm T&E is only rated at 32A, then upgrading to 10mm for compliance is a must.

In fact, you could argue that with them separated, you reduce the length of the cable which is exposed to the full current.

This is ONLY true for the sections of cable that supply the equipment, the cable from the Consumer Unit to the CCU would still be exposed to full current regardless of one appliance or 50 making up the cooker.
 
afaict it is perfectly allowed to put oven and hob on the same cuircuit

but whatever the regs say i would strongly advise designing a cooker cuircuit to the full rating of the appliances not the diversified rating

and i think fitting a new 16A cuircuit for the oven alone will be a lot cheaper and less work than replaceing the existing cooker cuircuit with 10mm
 
FWL_Engineer said:
If the two items were ONE appliance, then the total load would be some 10kW / 230V = 43.47A, so a single 6mm 32A circuit would not be sufficient to supply it.
I did say "Putting aside the arguments over the "10A + 30%" rule" - i.e. if you put the argument aside, that rule gives you a requirement for 19A, and that would be OK for the 6mm/32A circuit.

The circuit should be in 10mm and on a 40 or 45A MCB. Whilst, as I have said on numerous occasions, diversity should not be applied to circuits for cookers (IMHO),
Which is also what I said.. "It's not a method I agree with when designing a circuit, as it does assume that you will never turn everything on at once"

I think we can assume that is will normally only be used at about 80% FL, or about 35A, so a 40A MCB would suffice in this instance.
Why 80%? Why not 75%? 75% of the actual load (9.27kW, not 10kW) is 30A, so the existing 32A MCB would suffice.

As 6mm T&E is only rated at 32A, then upgrading to 10mm for compliance is a must.
So now it is my turn to take your comment to task. Whether you, or I, or anyone, disagrees with the (10A+30%) rule, you cannot say that it is not allowed, and since the application of that rule gives a 19A loading, then a 6mm cable on a 32A breaker is compliant.

If it was my kitchen, and it was going to be a sh*gging hassle to upgrade the circuit, or run another one, I think I'd suck it and see first.....
 
FWL_Engineer said:
If the two items were ONE appliance, then the total load would be some 10kW / 230V = 43.47A, so a single 6mm 32A circuit would not be sufficient to supply it.

I have a question related to this which i would love to get a few opinions on. I know this might be bending the regs, i just want to get some peoples practical experience, maybe BR, Securespark and FWL if they get a chance.

Q1. How much would a cable need to be overloaded by to pose a serious fire risk. I know generally this will never happen but just wondering.

Q2. If I buy a shower rated at 9.5KW, will it draw 9.5KW. I heard BR say before (correct me if i'm wrong) that somebody could connect a 9.5KW shower to a 40A breaker . (rated load 41.3A) Where is the tolerance here?

Q3. How much of a continues overload will an MCB handle?

Q4. When buying switches etc. what is the difference between inductive and resistive ratings.

Thanks, Declan.
Please pay particular attention to question 2. It is something i have often wondered about. How close to an appliances rating does it actually draw going full steam? :)
 
ban-all-sheds said:
If it was my kitchen, and it was going to be a sh*gging hassle to upgrade the circuit, or run another one, I think I'd suck it and see first.....

I suppose that is the difference between a professional and an amatuer :D:D
 
altec said:
Q1. How much would a cable need to be overloaded by to pose a serious fire risk. I know generally this will never happen but just wondering.

That is a hard question to answer, it will depend on the type of cable, quality of manufacture, quality of the equipment connected to it, the installation method and the ambient air temperature.

altec said:
Q2. If I buy a shower rated at 9.5KW, will it draw 9.5KW. I heard BR say before (correct me if i'm wrong) that somebody could connect a 9.5KW shower to a 40A breaker . (rated load 41.3A) Where is the tolerance here?

Unless the shower is one of the new variable Thermostatically controlled unit, then the shower will ALWAYS draw it's FULL potential current. The reason the MCB does not operate is because this is well within it's overload parameters.

altec said:
Q3. How much of a continues overload will an MCB handle?

That depends on several things, the "Type" of MCB (A,B,C,D), the duration and extent of the overload, and the heating this induces in the MCB.

altec said:
Q4. When buying switches etc. what is the difference between inductive and resistive ratings.

A resistive load causes less electrical stresses on the contacts of a switch that an inductive load. Inductive loads tend to cause sudden surges on energisation, this causes arcing between the switch contacts, this in turn causes pitting of the contact surfaces, which leads to switch failure, or even worse, it could lead to arcing during operation that, in theory, could cause a fire. That is the simple explanation :)

Hope that helps Dec.
 
FWL_Engineer said:
ban-all-sheds said:
If it was my kitchen, and it was going to be a sh*gging hassle to upgrade the circuit, or run another one, I think I'd suck it and see first.....

I suppose that is the difference between a professional and an amatuer :D:D

So you wouldn't entertain the notion that your arbitrary figure of 80% might be wrong, and another arbitrary figure of 75% might be right? Or that even if a safe and compliant way of powering the cooker with 6mm cable actually worked, that it should be left alone?
 

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