Connecting ovens under the 17th edition regs

[Knickam]

Hi All

We are at the early stages of a self-build project and my query
Is regarding wiring ovens under the new 17th edition regs.

We are planning to have 2 separate single ovens and are aware
That oven elements can cause RCD’s to trip due to current leakage.

The ovens will be on the opposite side of a 100MM stud wall from the C.U.
So if they are fed directly off the switch in the C.U. does that mean
They will the have to run in protected cable (wire armour) under the
New regs?

Would also like to know any views on having a single or separate
feeds from the C.U. for the ovens. The ovens will probably be rated
3.7KW

Are there any other appliances that can have earth leakage problems?

Thanks in advance

Ian

 

[stephenf8542]

Why wire armour?
virtually anything with a motor has earth leakage

 

[ericmark]

In theory to trip a 30ma trip with a single item would means it would come under the high leakage category and would also need extra earths as a result.

In practice is an oven is left for a long time without use it can absorb moisture and have high leakage a minute or so after first switch on.

It is unlikely that an oven feed with it's own RCBO will exceed 15ma needed to trip it. However if you are worried you can get Ali-tube cable designed for use in stud walls.

Fridge/freezer is another consideration.
Any RCD may cause failure of supply through atmospheric conditions or faults on other appliances so supplying from it's own RCBO will reduce chance of failure.

But on its own RCBO you may not notice it has tripped.

 

[Knickam]

Why wire armour?

I gave this as an example of one of the options for protecting a cable
less than 50mm deep in a stud wall.

 

[stephenf8542]

If its a new build then your C/U will be rcd protected.The less than 50mm requires rcd protection which you will have so you'll be covered.

 

[ColJack]

RCD protection is not a cure all fix..
the cables have to be within the "safe zones" for it to be used..

 

[Chri5]

The oven circuit should include local isolation in the event of a need to switch off. Using the CU MCB as the only method is both wrong and dangerous.

Is each oven going to be 3.7kw ? What will the hob be. if it's a ceramic one then you might need to consider that.

 

[flameport]

One circuit will be adequate for the majority of installations, including most examples of :
1 single oven
1 double oven
2 single ovens
1 single oven and electric hob
1 double oven and electric hob.
1 electric cooker - hob and oven(s) conbined into one unit

If you have a gas hob, it will just need a low power connection for the ignition, so again, 1 circuit will be fine.

You may need 2 circuits if a double oven and high power electric hob are fitted, depending on the rating of the appliances. 2 circuits would probably be required for 2 double ovens, but that is an unlikely arrangement in a domestic property.

Induction hobs will inevitably need a separate circuit, which just adds to the already gigantic costs of these hideous devices.

An isolator switch should be fitted to the wall near to the hob/ovens (but not directly above the hob).
The most flexible option for connections behind the oven is a dual gang flush mouted box. You can then fit various items there as required:
2x cooker plates
1x cooker plate and 1x 13A socket
2x 13A sockets
depending on the appliances you have.

RCDs - if a new appliance causes a 30mA RCD to trip on its own, the appliance is defective and should be replaced.
Heating elements do have a small amount of leakage inherent in their design, but this is 1 or 2mA, certainly nowhere near enough to trip an RCD.

 

[Knickam]

Thanks for all the comments,

So if I have got this correct I can have,

1 induction hob (7090w) on its own 32amp circuit with a local 32amp isolatotion switch and either

2 ovens (3700w each) on a single 32amp circuit with seperate 16amp
isolation switches.

Both circuits protected by an RCD and cables run in the safe zones.