Power to Oven and Hob

[r.rain]

Hello All

Can someone tell me if my existing cooker control unit which is currently controlling a Baumatic gas range will be able to power my new ceramic hob and double oven? The current control unit is on a seperate circuit protected by a 32 Amp MCB and the wiring is thick stuff with multi strands as opposed to solid thick cores.

The KW details of the new appliances are as follows:

Baumatic Double Oven fuse rating 20 AMPS

3.95KW

Baumatic Ceramic Hob fuse rating 30 AMP

1 x 0.75/2.20 KW double ring 1 x 1.80 KW 2 x 1.20 KW

I would like to simply wire the new hob and oven into the existing junction box where the existing gas range is cabled into.

I have done some searching on this one and have found some good information, one posting stated that if the load was below 7KW it would be fine but it also stated that it may be fine if it was over 7KW and I didn't understand the diversity part.

Thanks for your help with this. It will be an absolute nightmare to get another cable back to the CU. I cant get access to it due to wardrobes being built over the floor boards directly above it and Ive just had the walls in the kitchen drylined!

Any other alternatives anyone can think of, I could buy a new CU but where would be best to site that and what would be the best way to run the cable through a dry lined solid wall back to the new CU Cheers

Richard

[Lurch]

On 15 Dec 2004 03:15:14 -0800, [e-mail] strung together this:

In simple terms, diversity is the fact that you're unlikely to have all the rings and all the oven\grill elements at once. Basically, I wouldn't worry about connecting that up to your supply.

[Owain]

Richard wrote | Can someone tell me if my existing cooker control unit which is | currently controlling a Baumatic gas range will be able to power | my new ceramic hob and double oven? The current control unit is | on a seperate circuit protected by a 32 Amp MCB and the wiring | is thick stuff with multi strands as opposed to solid thick cores.

Good so far.

| The KW details of the new appliances are as follows: | Baumatic Double Oven fuse rating 20 AMPS 3.95KW

3.95kW = about 16A (max)

| Baumatic Ceramic Hob fuse rating 30 AMP | 1 x 0.75/2.20 KW double ring | 1 x 1.80 KW | 2 x 1.20 KW

about 26A (max) if my maths does not fail me.

Total 42A.

| I would like to simply wire the new hob and oven into the existing | junction box where the existing gas range is cabled into.

You can wire both into the same cooker control unit provided that the switch is within 2m of each appliances (and provided the terminals are big enough to take the cables).

| I have done some searching on this one and have found some good | information, one posting stated that if the load was below 7KW it would | be fine but it also stated that it may be fine if it was over 7KW and I | didn't understand the diversity part.

7kW is about the max load for a 32A circuit, with no diversity.

Diversity assumes:

1. That you won't have all five rings and both ovens on at the same time
2. Even if you do, they will be cycling on and off on their thermostats

So the idea is that you can run a 42A *max* demand appliance on a 32A circuit because the max concurrent demand will not be reached.

However diversity has to be calculated according to the likely use of the appliances; there is a standard formula (which I can't remember) but it is for ordinary domestic use. It won't apply if your cooker gets used more heavily (B&B/guesthouse, home catering business, large family at christmas). It's something of a judgement call, but it will be probably OK.

Owain

[BigWallop]

What length would you reckon the cable is? And roughly how many strands, and how old?

The use of a 32 Amps MCB for protection on this supply would make me think that the cable is 6 mm csa' to the cooker unit. Depending on the length of the cable at that size of cross sectional area, the total loading can be up to 40 amps if it's 6 mtrs or less in length.

That's roughly 9 kW (approx' 38 amps) in total at full load, so this might cause some annoying cases of the 32Amps MCB tripping off if the whole lot is switched on at the same time.

Diversity comes in to play with appliances that contain individual small loads that should never all be on at the same time because of timers or thermostatic controls.

On an installation with a total power capacity of nearly 9kW, I personally would not rely on the diversity rule. You may find times, like the Christmas Dinner, when all the heating elements will be needed all at the same time. In this situation the cable might hold integrity, but the 32 Amps MCB will trip off because of the over current.

Check the total length of the cable. Grey PVC T&E cable depends on its total length as what Amps rating it will carry safely.

Check how many strands. If the cable has 7 strands it's most likely 6 mm csa' so it then depends on its total length. If the cable has 12 strands it's most likely 10 mm csa' so should take the total loading but will need a

40 Amps MCB to take the total load rating of your new appliances.

[r.rain]

Thanks, so what if I did turn on everything would that trip the MCB? just thinking about family get togethers and christmas, not that my kitchen will be ready for then mind. Thanks again for your quick answer Richard

[Stefek Zaba]

That's your privilege, of course: but the diversity guideline in the OSG (count a cooker - and a hob-n-oven counts as a "single" cooker for this porpoise) - has stood installers and householders in good stead for several decades now. Yer 9kW worst-case isn't even 40A (it's 36A in my quick rule-of-thumb 1kW=4A; with the unrealistic use of 230V as the supply voltage it's 39.1A. Unrealistic because no-one changed transformer taps across the country when the Europe-wide descriptions of voltage bands were widened around a 230V nominal, so we're all still on

240V "really").

No, the 32A MCB won't trip. First of all, the 9kW won't last for more than a couple of minutes, if that - even running flat out to do the full Christmas overeating experience, rings and ovens (not grills) have "simmerstats", "thermostats", or similar devices which mean they're not powered up constantly, but are switched on and off over periods of tens of seconds for rings, minutes for ovens. (It's this fact which lies behind the accepted diversity guideline.) Secondly, the 32A MCB will pass even 40A more or less indefinitely - for a 25% overload such as this, it would take several *hours* for the MCB to trip.

[r.rain]

Very interesting. Well from memory the cable has 6 or 7 strands and from CU to cooker control unit is probably 3-4 metres maximum, the cable is relatively new I think as the house was re-wired failry recently not exactly sure when though.

Thanks!

Richard

[Lurch]

On 15 Dec 2004 06:00:37 -0800, [e-mail] strung together this:

Not neccesarily. A 32A won't trip at 32A, it could quite happily run at slightly over for a lengthy period of time without tripping. You could also run at a fair amount over 32A for a shortish period of time quite happily. I would be quite happy connecting it, if it does concern you connect it all up then turn everything on and leave it for a while. If it does cause a problem then I can imagine it will be a fairly major job rewiring the circuit which is the only other option.

[Mike]

An MCB tripping is simply nature's way of telling you not to turn all the elements on :-)

I'm sure after the first time it does your wife will learn not to.

[ARWadsworth]

And the OSG says a 32A circuit is usually appropriate for a household cooker rated up to 15kW if that helps ease your mind.

Adam

[r.rain]

Great stuff, thanks for all your feedback. On the same circuit it goes. Cheers!

Richard

[andrewd909]

When we had our kitchen fitted a few months ago the fitters wanted seperate cicuits for the oven and hob, they said that Bosch insisted on it, they had known of a warranty claim being refused because of wiring both on the same circuit

[Owain]

wrote | When we had our kitchen fitted a few months ago the fitters | wanted seperate cicuits for the oven and hob, they said that | Bosch insisted on it, they had known of a warranty claim being | refused because of wiring both on the same circuit

Possibly because Bosch expect their European kitchen appliances to be connected to European 20A radials, instead of a properly muscular British

32A/45A cooker circuit. I hope such beastliness is never tolerated in our Wiring Regulations.

Owain