Electric Oven and Hob Wiring

[davas]

Hello all,

I've recently had my kitchen fitted and the following problem/query came out when the fitter was discussing the electrics for the single oven and ceramic hob.

During my rewire I had fitted a dedicated circuit into the CU for the "cooker" on a 40A MCB, RCD protected (due to 13 amp socket on the cooker isolator switch), using 10mm cable and a cooker connection unit/plate at the end of the radial.

So the config is as follows

CU (40A) --- Switch --- CCU

Oven is 2.5kW, and hob is (6.0kW).

The fitter suggested that the oven should not be fitted (along with the hob) into the connection unit. He mentioned something about it only drawing less current so wouldn't have appropriate overload protection (i guess he meant there was no fuse between it and the MCB and the difference between 10.8A and 40A is a lot).

Could you please tell me if this is the case and if wiring them in together is safe or not?

Also, given that my units and worktops have all been installed what are my options for rectifying the situation?

Thanks in advance for anyone replying!

Chris

 

[Steve]

Connect the hob direct to the cooker outlet, and fit a single unswitched socket to this in the same manner. This is easier if you have a cooker outlet behind the oven (small box fed by the cooker control unit, serves as a connection point and junction box).

Wire the socket in 6mm², simply because it will be VERY tricky to get 10mm² into a socket without cracking the faceplate!

 

[davas]

thanks for your advice!

Reading the oven manual it states that it should not be connected using a plug so I would assume a FCU would do exactly the same job.

Out of interest why should I not connect both into the cooker connection point? Surely that is equivalent to having a single freestanding cooker unit in terms of circuit-load etc. Where is the problem in doing this?

 

[Steve]

The wiring inside the oven is not rated to 40 amps. In a freestanding cooker it would be.

And if the oven says "connect to a 13A supply" or similar, this is what you must do, or the guarrantee will be null and void.

I just re-read. Is this a single oven? Is its total possible rating actually 2.2kw? I need to be sure. What does it say its supply requirements are in the manual?

 

[securespark]

The wiring inside the oven is not rated to 40 amps. In a freestanding cooker it would be.

So, in a free-standing cooker, all the conductors feeding switches and elements, etc, are rated to 40A?

 

[plugwash]

maybe its protected by something inside the cooker, maybe they have calculated that significatn overcurrent is highly unlikely and that there will be sufficiant short circuit protection from the fusebox, maybe they have decided that the internal wiring isn't in a place where its failure would be likely to cause danger (cookers are generally made of pretty heat resistant materials).

whatever method they choose to use to protect/justify the wire sizes they use its their problem to ensure that they are safe for connection to a circuit big enough to power the cooker.

if on the other hand you choose to ignore a manufacturers reccomendation on the protection an appliance is connected to you cannot assume that it will be adequately protected.

 

[davas]

The wiring inside the oven is not rated to 40 amps. In a freestanding cooker it would be.

And if the oven says "connect to a 13A supply" or similar, this is what you must do, or the guarrantee will be null and void.

I just re-read. Is this a single oven? Is its total possible rating actually 2.2kw? I need to be sure. What does it say its supply requirements are in the manual?

The manual says...

This appliance must be earther and connected to a 230 Volt, 50 Hz, single phase supply through a suitable control unit with a fuse rating of 20 amps. The control unit should incorporate a double pole switch having a contact separation of at least 3mm in all poles and should be located adjacent to the oven to allow easy access in case of emergency...

Alternatively the mains supply can be taken from a household 13amp switched fused spur. Having a minimum contact clearance of 3mm, which must be fitted adjacent to the oven housing cabinetry and accessible after installation. The oven must be fitted with 3 core cable having a minimum cross section area of 1.5mm and must conform to BS6500. The oven must not be connected using a 3-pin 13amp plug.

The rating on the box states it is 2360W (By my calc is 10.2A).

 

[Manty]

I can't see why the manufacturer says you cannot wire it to a plug based on that rating - your kettle is likely to be more powerful than that. It's possibly for convenience of not having a fuse behind the oven... ?

Sorry to hijack, but I also have a similar situation, 2.5kw oven, and debating wether to wire it with a plug (manual does not mention plugs, just says 20amp feed, but I think thats to comply with continental wiring systems).

I have some heat resistant butyl flex for the oven, and I'm thinking of wiring this to a dedicated cooker outlet behind the oven, which itself will be fed from an FCU above the worktop (using 2.5 t&e)... anyone see a problem with that?

 

[Steve]

The manual says...

Alternatively the mains supply can be taken from a household 13amp switched fused spur. Having a minimum contact clearance of 3mm, which must be fitted adjacent to the oven housing cabinetry and accessible after installation. The oven must be fitted with 3 core cable having a minimum cross section area of 1.5mm and must conform to BS6500. The oven must not be connected using a 3-pin 13amp plug.

The rating on the box states it is 2360W (By my calc is 10.2A).

A 13 amp switched fused spur is the same protection as a 13 amp plug. Rather than fitting a new socket, I would just do as it says and use a fused spur down there instead.

Manty, I dont see a problem with what you propose. So long as the maximum the whole appliance can draw is 2.5kw. Ie. theres no grill / second oven that can be used simultaneously with the oven.

 

[plugwash]

iirc the reason manufacturers say you shouldn't wire something to a plug is nothing to do with safety, its to do with getting arround the european legislation requiring fitted plugs.