Connection for built-in oven

[DavidA]

Hi

I am replacing a built-in oven. The existing oven connects via 6mm T&E directly to the consumer unit (there is no junction box near the oven).

Please can anyone point me to regulations for connecting a built-in oven? Is a local junction box / fuse unit required?

Also, please can anyone point me to the current carrying capability for 6mm T&E ?

Best regards

David

[NT]

NT

[DavidA]

Hi NT

Thanks for the link to the cable info.

Does anyone have any thoughts on my other question:

David

[ARWadsworth]

What does the installation manual say regarding the fuseing?

Cheers

Adam

[DavidA]

Good point. I will download it and have a look.

Thanks

David

[DavidA]

Th Neff manual states:

"In the installation, there must be an all-pin isolating switch with at least 3mm contact gaps, or the appliance must be connected using a plug with an earthing contact. This must remain accessible after installation."

I can't see that a plug is an option, because the oven is rated at

5.7kW. So does that mean I need some kind of oven isolating switch, or will the MCB at the consumer unit be sufficient?

David

[DavidA]

Sorry, I have just realised that there is an isolating switch for the oven, but it is at least 3m from the oven. Am I right in thinking that the Building Regs require the switch to be within 2m of the oven?

Would this not apply to me because it is an existing installation?

Best regards

David

[Jim K]

is it a double oven? have you added up both ovens ratings to get to

5.7kw?

if so google "diversity electrical"

Cheers Jim K

[Tim Watts]

On Mon, 14 Jun 2010 12:12:31 -0700, DavidA wibbled:

Let's assume "all pin" means L+N which is almost certainly what they really mean. You generally don't switch the earth out.

Well, they do 32A "commando" plugs. Likely in a commercial kitchen but you probably don't have room - they're fairly lumpy buggers - would take a chunk out of one of your cupboards and you wouldn't be able to fit one behind the cooker.

Standard 2 pole cooker isolator will be fine.

The MCB as an isolator will not be fine for two reasons: firstly, nearly all[1] domestic MCBs/RCBOs are single pole (L only). Secondly it will be far removed from the device. Local isolation is a good idea (can't remember if it is positively required). If it is hideously difficult to fit a local isolator, I or someone else here will no doubt be able to look up the regs chapter and verse if you ask.

[1] I do have a couple of DP RCBOs - but they are far from normal.

Re fusing: 32A MCB at the CU will be the nearest rating. Your oven draws more than 20A which would be (AFAIK) the next common rating down. It's possible the oven manual might suggest a 20A MCB based on its load characteristic[2] which is why the question was raised, but in the absence of any other information other than 5.7kW, it would be a reasonable assumption to go with the 32A MCB.

[2] eg it might pull 5.7kW for a short while from cold then the thermostat will cycle it to a lower average power draw. Unlikely I would have thought - it will probably take some time to reach operational temperature. My combi can preheat to 250C in about 5-6 minutes, but it's fairly little and fan assisted. Bigger ovens IME take rather longer.

6mm2 cable will be fine under these conditions unless it is run is a cruelly non optimal way (eg bundled with a bunch of other cables, hot water pipes and buried in insulation!)

[Tim Watts]

On Mon, 14 Jun 2010 13:30:51 -0700, DavidA wibbled:

The IEE OnSite Guide (17th) says 2m specifically, but does not cite a specific regulation. Skimming through section 537 in the actual regs which deals with isolation and switching, I don't see any reference to cooker circuits or kitchen appliances (though I may have missed it - oh for a searchable PDF!).

It is possible that this is drawn from some other non IEE regulation or it's also possible that it is merely accepted good practice and you could ignore it as long as you do have an isolator somewhere if meeting

[Frank Erskine]

In fact it's _very_ bad practice to switch the earth, from a bonding point of view.

The isolator for my Bosch double oven doubles up for the (also Bosch) ceramic hob - both are (as the crow flies) within about a yard of the isolator inside a cupboard almost below the hob.

(Within that self same cupboard is my stash of real tungsten lamps, btw). And a few other things...

[Jim K]

the mind bugles :>)

Jim K