Amp and cable question.

[pz8d3r]

Hi, I'm buying a Falcon range cooker. It's rated at 15.2 kw and will be sited about 10 meters from the fusebox.

Could anyone here tell me what amp fuse it will need? Is it kw=v*a (i.e. 66amps)? Also what size cable will it need? The cable FAQ doesnt go that high.

Thanks.[/url]

MOD

moved as posted in wrong forum

 

[pna]

Thats one big cooker!

In theory, yes 66A, but in practice, probably not as much as this.

You are probably looking at 10mm cable, but as this work is subject to part p, you should probably just get someone in.

 

[scoobydooby]

run 10mm cable and put it on a 45 amp fuse

 

[felix]

Is that 15.2kW the maximum power consumption? The let-out with a cooker is that, in practice, not everything will be running flat out all the time. Rings and ovens have thermostats that cause them to cycle on and off so the AVERAGE current is much less.

I've just dug up some information about cookers. It might be out of date in which case I can expect an ear bashing quite soon ---

"The first 10 amps is rated at 100% and the remaining amps are rated at 30%."

If this is still correct then in your case you have an average load of 10 amps + (0.3 x 56) = 16.8 amps, ie a total of about 30 amps. If your cooker switch has a built in socket you have to allow extra for that; 5 amps according to this old book.

The only thing bothering me here is that you call it a 'range' cooker. This sounds like something with half a dozen rings and four ovens. If this is the case then that 66 amps might be the average consumption already. Have a close look at the connection instructions. Do the words "three phase" appear anywhere???

 

[Big_Spark]

I have said it before and I will say it again, applying diverstity to a cooker is dangerous. There are times in a year when a cooker may be used at full capacity, such as Christmas, unplnned for social gatherings etc..it happens and a lot more often than many here give the impression.

10mm T&E is on the bottom end of the scale, to be honest I would recommend installing 16mm T&E or 10mm SWA to ensure that the cable is capable of withstanding the full load should it ever be drawn.

There is also the matter of Cooker Connection Units and DP switches, these are rated at 45A, and so the usual connection method is defunct.

My last comment would be this..are you really sure that the cooker is 15.2kW....that is larger than many industrial units and frankly it sounds wrong.

 

[plugwash]

is it a combi electric/gas and if so are you looking at the full power rating.

 

[theshogun]

I have a range cooker rated 15.6kw i wired it in 10mm t&e cable, via 45d.p switch.
When i installed it i put it on a b32amp mk mcb with the possibility of uprating this if i had any problems, i have yet to change this in 4years ,the only time it has tripped is when an oven element blew short circuit.

In this time we have had plenty of family gatherings where the cooker has been used to capacity,however the cooker is not at this load for long,for the reasons felix has stated .(diversity)
I would run 10mm t&e cable using the 45amp 2gang double pole switch rather than a cooker control unit as you dont want to plug anything else onto this cicuit.

 

[Big_Spark]

Shogun, just because the MCB has not tripped doe not mean your not overloading it.

If it is a Type B MCB, then it's operational range is 5 - 10 times rated current momentarily (about 5 seconds usually), however to load it up by 50%, which is all you may be doing, is not stressing the breaker enough to operate it. Most MCB's, if the loading is gradual and steady, can be loaded to around twice their rated current before operating. This amount of overloading will vary with Breaker type and even manufacturer.

This is the main reason why diversity should not be applied to such heavy load devices as cookers.

 

[theshogun]

Most mcbs will take 1.5 times rated current for a period of time before tripping ,this is done thermally within the mcb how ever the mcbs are designed with this in mind so it cannot be overloaded to the point of damaging the installation .
In my view of this in the domestic setting ,cookers which take variable current load due to everything not being on at once, thermostats cutting ovens and ring out when temperature is reached ,do not really take /draw the full rated current , at any one time for long enough to cause damage to the installation.
The majority of the time/meals cooked the cooker draws about 15 amps nowhere near overloading the mcb i have installed and certainly not the cable.

 

[Big_Spark]

Shogun, with respect your view is not relevent, same as mine isn't, all that matters are the facts...

MCB's are designed to accept about 1.5x there rated current, you are correct, that is what i said above, however that does not mean it is correct or safe to consistantly overload the breaker, and running a breaker beyond it's manufacturers rated capacity is overloading.

 

[mapj1]

The saving grace to many such installations is that in the same way the MCB takes time to heat up and trip, so does the wiring take time to heat up and do damage, and the time constants in the breaker are such that the worst you will normally do is have to change the breaker one day when it trips and refuses to reset, the wiring, which is what causes the fire if it overheats is normally OK, unless actually under-size or terminated badly.
Over running cable is not good, but the effect of small overloads (I mean temperatures below PVC melting point, perhaps 90-105c instead of the design temperature of 70, corresponding to perhaps 150% of the normal temperature rise, and power dissipation ) is not an instant and catastrophic failure , but more a premature aging of the cable. For this reason many under-specified installations will run on happily for many years being overloaded for perhaps an hour a day or so, whether advisable or not.
If you doubt this, consider that mercifully most broken ring mains are discovered by testing when later work is done, and not by the fire brigade investigation teams (and I fear there are plenty more broken rings out there waiting to be found).
However, there is no real excuse to install something from new as borderline, so please either use the next size up cable, (or next size down in breaker).

 

[Damocles]

Wiring regulations are written with the idea of doing a safe job. regs say the load of a cooker can (safely) be de-rated as described earlier. MCb, fuses etc are designed to safely ptotect circuits under all possible conditions.

I am sure there are plenty of houses around where the single ring for the whole house is operating at the maximum capacity its fuses will allow and that this is greater than their nominal rating. The wiring has been designed as a system which assumes that the quoted ratings are nominal and can safely be exceeded from time to time.

Possibly the cookers instructions have something to say on recommended mcb rating?

How many times did chief engineer Scotty complain that 'the engines canna take it'? Never blew up, did they. (couldn't resist)

 

[pz8d3r]

Thank you all for your posts. I've checked the cooker. It's a Falcon 1092 professional all electric range (www.falconappliances.co.uk), 2 ovens, 1 grill and a 6 element ceramic hob. The total rating in the documentation is 15.2kw. It's not triple phase.

It's obviously a matter of some debate as to the loading but for safetys sake I will err on the side of caution and call in an electrician to upgrade the wire to 16mm and modify the equipment accordingly.

 

[pz8d3r]

Just to let you all know, I contacted the manufacturers technical department.

They advised that cooker could run just fine on a standard 32A circuit but that "it could trip the mcb under heavy load, for example at Christmas time"

They said that they recommended upgrading the cable to 10mm and putting in a 45A mcb, which would be fine.

I ran the cable in myself and upgraded the mcb accordingly. I'm glad I didn't have to put in 16mm as the 10mm was a pig to run in.

 

[delmel]

cookers do generally have the diversity formular applied. The correct formula is to count the first 10amps + 30% of the remainder + 5amps for a cooker socket if applicable. Obviously bigger the cable the better, but remember it does need to be terminated and fused correctly

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