Why don't they......

Hi All,

I'm remodelling a kitchen and currently I've got a 6mm feed going to a double oven, which also feeds a microwave.
Oven is rated at a 4kW Max Load (from the product fische), Microwave is a 900W unit.

Oven fische also says this....................
Energy consumption: 0.81 kWh (venting)
Energy consumption (oven 2): 0.71 kWh (conventional)

My Maths is a bit rusty but I can't get that to equal 4kW...........................

As part of the remodel the Cooking Tower and the Integrated Fridge Freezer tower are being placed next to each other.

What I'd like to be able to do is extend the radial feed to add another single socket for the fridge.

Can I find the max instantaneous demand for the fridge/freezer............................ Can I b@lls, only thing I can find is 246 kWh consumption (Aec)

My thoughts are, that with the considered diversity then the 6mm and 32A RCBO will be appropriate.

What do you guys think? I could stick a cheap power pass through socket power meter on it for a week and see what the peak draw is over the period. Does anyone think that's necessary?

Cheers
Lee

LeeJC said:

Hi All,

Oven is rated at a 4kW Max Load (from the product fische), Microwave is a 900W unit.
Oven fische also says this....................
Energy consumption: 0.81 kWh (venting)
Energy consumption (oven 2): 0.71 kWh (conventional) ..... My Maths is a bit rusty but I can't get that to equal 4kW...........................

Click to expand...

Those are energy consumption figures (in kWh) and so represent the amount of energy used when the appliance is drawing in a certain amount of power (kW) for an (unspecified!) period of time.

If it's as simple as this (probably not!) 0.81 kWh plus 0.71 kWh comes to 1.52 kWh,and if the over really does draw 4 kW continuously (very unlikely), then one would expect it to consume 1.52 kWh of energy in about 22.8 minutes! Those energy consumption figures may possibly relate to one hour of 'normal operation' (during which the oven will not be drawing 4kW continuously, because of thermostatic control).

Kind Regards, John

LeeJC said:

I'm remodelling a kitchen and currently I've got a 6mm feed going to a double oven, which also feeds a microwave.
Oven is rated at a 4kW Max Load (from the product fische), Microwave is a 900W unit.

Oven fische also says this....................
Energy consumption: 0.81 kWh (venting)
Energy consumption (oven 2): 0.71 kWh (conventional)

My Maths is a bit rusty but I can't get that to equal 4kW...........................

Click to expand...

It is not maths alone; it includes time. It is like how many miles in thirty miles per hour.

When on for an hour it only uses 0.71kWh instead of 4kWh, or -
4 / 0.7 = 5.71 means that when your oven is on max (conventional) it is only using the equivalent of 4kW for 10.51 (60 / 5.71) minutes.

LeeJC said:

As part of the remodel the Cooking Tower and the Integrated Fridge Freezer tower are being placed next to each other.
What I'd like to be able to do is extend the radial feed to add another single socket for the fridge.

Can I find the max instantaneous demand for the fridge/freezer............................ Can I b@lls, only thing I can find is 246 kWh consumption (Aec)

Click to expand...

Is that annual?

LeeJC said:

My thoughts are, that with the considered diversity then the 6mm and 32A RCBO will be appropriate.

Click to expand...

You don't need diversity with only 4.9kW of cooking appliances.

Is the double oven only 4kW - not 4kW each?

LeeJC said:

What do you guys think? I could stick a cheap power pass through socket power meter on it for a week and see what the peak draw is over the period. Does anyone think that's necessary?

Click to expand...

The fridge will be fine on the circuit.

Label the consumer unit appropriately.

Pretty similar in my old house, 6mm feed with a 32a mcb (went all through the ceiling/insulation etc) feeding a dual fuel range cooker with about 7.2kw max load, cooker socket also had a socket which ended up having a toaster on.
Diversity made things just fine, nothing ever got overloaded or tripped

I’ve stuck the power meter on the fridge just out of curiosity more than anything

Product fische isn’t the greatest but I’m reading it as a 4kW max load. Top oven seems to be 4Watts……

Thanks for the replies gents. Appreciated.

Also this:

Still not clear but it does say total power 4,000W.

(A 4W oven wouldn't be much use. It does then state 4,000W below that)


Either way, it is still not huge.

We measure energy as Joules, however the numbers become rather large, so watt is a Joule per second, so a Watt hour is 60 seconds x 60 minutes 3600 larger unit to the Joule, so we have another unit 3600 times bigger, clearly neither having any connection to the metric system which means we have a third unit again larger that the Joule there are 4.2 Joules in a calorie, I loved writing about calories in school as a Calorie is 1000 times larger than a calorie so can start a sentence with a small c.

So three units of energy, Calorie, Joule and Watt/hour. And just to confuse a Watt hour has nothing to do with time, the hour cancels out the second which is part of the watt.

So we measure what some device uses. This is the result of measuring what my tumble drier uses, the energy is the area under the graph, power is the graph, and it is near impossible with my maths to convert that graph into energy. The fact it switches the heat pump on/off at latter part of cycle, means only way is to have a device which measures energy direct, same with fridge that does not help, and this is the bit we need from the energy meter software, showing what the fridge has used until 13:40 today. This means it is even harder to work out cost, not helped with a in house smart meter display showing if one looks very careful it says 1.76 kW export, but such a small increment on the scale one needs to pick it up to read the values.

If one tries to measure what a non heat pump tumble drier uses, or an immersion heater (unless using an iboost+) it is easy to work out energy used, as straight line graph, but a hob, oven ect, it turning on/off all the time once it has reached the temp set.

We are allowed to use diversity, as it is assumed that all items will not switch on together, and since the thermal damage or tripping of a thermal over load takes time, if for a few seconds the load exceeds the MCB rating it does not really matter, it would for a type B have to be between 3 and 5 times the MCB rating to cause a problem, when it would trip the magnetic part of the trip.

Where it does cause a problem is when the power comes from an inverter, having a B16 MCB on an inverter or for that matter a small generator of any type, it will likely not trip with even double the load so 32 amp will not trip it and damage will likely result, so faster trips are required, the like of the semi-conductor fuse.

This caused a big problem with Spanish and French smart meters, unlike us, often the supply was limited to 16 amp for whole house, and the fuse would allow for the diversity, so exceeding 16 amp for a minute raising to 20 amp, then down to 10 amp, the fuse would hold, but smart meter would trip.

So with a 4 kW oven clearly needs a 4 kW supply, but two 2 kW ovens may work fine with a 3 kW supply (although not recommended) as one will start cycling before the other is switched on. In some cases the device like a hob is designed so the heat areas take turns in using the power.

I would guess the 4 W is the fan, not the heating element.

ericmark said:

I would guess the 4 W is the fan, not the heating element.

Click to expand...

Maybe, but I would be much more inclined to suspect that it is a typo!

Oven 2 is conventional so no fan, it’ll be a typo.
I could pull it apart and find out but my suspicion is it’s got 6x1kW elements for hi/lo grill, top and bottom ovens.

Where did I put my screwdrivers……

Actually got 3 according to the spares list.
1800W Fan & 900/1300W conventional.
Who knew….

ericmark said:

so watt is a Joule per second,

Click to expand...

Ok.

ericmark said:

so a Watt hour is 60 seconds x 60 minutes 3600 larger unit to the Joule...

Click to expand...

Sort of - but not really. Is the OP's 0.71kWh another unit?

ericmark said:

...And just to confuse a Watt hour has nothing to do with time, the hour cancels out the second which is part of the watt.

Click to expand...

LeeJC said:

Oven 2 is conventional so no fan, it’ll be a typo.
I could pull it apart and find out but my suspicion is it’s got 6x1kW elements for hi/lo grill, top and bottom ovens.

Where did I put my screwdrivers……

Click to expand...

It doesn't matter for your query of adding a socket.


The specifications do not really make sense.
In the link I found it says oven 2 is the small one yet that is the one for which all the figures are given and which has the fan; nothing is shown for oven one.

EFLImpudence said:

It doesn't matter for your query of adding a socket.


The specifications do not really make sense.
In the link I found it says oven 2 is the small one yet that is the one for which all the figures are given and which has the fan; nothing is shown for oven one.

Click to expand...

You’re right of course. And thanks all for the responses.
Shouldn’t be surprised that manufacturers specifications which are pretty important aren’t clear

EFLImpudence said:

Sort of - but not really. Is the OP's 0.71kWh another unit?

Click to expand...

So 2.566 MJ then using the metric system, nearly a horse power, 0.952124 Horse power. Was that 550 foot/pounds.

This is the problem being an old fogy, I was taught to use LSD and that not a drug.

I thought a horse power was 745 Watts all day.

EFLImpudence said:

I thought a horse power was 745 Watts all day.

Click to expand...

about 745.7 I believe