Another built in oven question

[Brigman]

I don’t know a good sparky so want to arm myself with some knowledge just in case the guy from the yellow pages tries to quote me something silly for unrequired work or preferably do it myself:

I\\\'ve just purchased a new bosch built in oven (model HB13550) to replace a 7 year old Smeg. The previous oven was wired to a cable with a 13 amp plug at the end with a double wall socket sitting behind the oven which also supplies the hob ignition.

The double wall socket then runs up to a cooker isolation switch (the normal thing with the big red button) which sits above the kitchen unit.

The new oven is 2.8kw so I assumed I could just wire the oven to the old cable, plug it in and hey presto. However, the instructions explicitly say not to connect the oven using a 13amp plug and fuse but I\\\'m not sure why or what else I can replace the 13amp plug with? Do you think the instructions are just generic and apply to ovens above 2.8kw, or maybe say that to stop people plugging the oven in to a circuit without an isolation switch? Is there a higher rated fuse plug required?

Any advice greatly appreciated...

 

[DJDUNKY]

The new oven is 2.8kw so I assumed I could just wire the oven to the old cable, plug it in and hey presto. However, the instructions explicitly say not to connect the oven using a 13amp plug and fuse but I\\\'m not sure why or what else I can replace the 13amp plug with? Do you think the instructions are just generic and apply to ovens above 2.8kw, or maybe say that to stop people plugging the oven in to a circuit without an isolation switch? Is there a higher rated fuse plug required?

If the oven is rated at 2.8kW then technically you can plug this into your double socket with a 13A fuse and plug, behind the cooker that is isolated from your cooker control switch. I would change the MCB to 16A in the consumer unit though as it is probably a 32A one and the cooker control switch if it has a socket on to one without, that's if you have an MCB board and not fuses.

The manufacturer is covering themselves by saying DO NOT USE 13A plug imo.

 

[Brigman]

Thanks djdunky,

The current isolation switch has a socket which we use for the kettle and we've had no problems with this and the old oven. Is this something we really need to do? I'm obviously just trying to avoid electrician costs here...

 

[DJDUNKY]

An oversight -

Check the MCB to see what size is currently protecting this circuit because if as you say you have a double socket behind the cooker then unless that is being supplied from it's own FCU then this needs to be changed as the double socket is only rated at 13A so the circuit protection isn't good enough if the circuit as a whole has a 32A - that being the only protection!

You could, as you say, leave the cooker control unit as it is at the moment and plug your kettle in assuming:

1.) The cable on that circuit is big enough
2.) The double socket behind the cooker is protected by it's own FCU if the MCB is 32A
3.)

 

[davy_owen_88]

if as you say you have a double socket behind the cooker then unless that is being supplied from it's own FCU then this needs to be changed as the double socket is only rated at 13A so the circuit protection isn't good enough if the circuit as a whole has a 32A - that being the only protection!

What? Are you saying every socket in the UK has been installed incorrectly and every socket should have an FCU before it?

The CPD is there to protect the cable, that's it. And although a socket is rated at 13A that is only the bit between the rear terminals and the front I.e 13A being drawn through it continuously by a load plugged into that socket. It doesn't relate to the current that could be flowing in the cables connected to the rear. If it did then ring circuits and radial circuits protected by 32A/20A MCB's feeding 13A sockets wouldn't be allowed.

If the cable is protected then there is no problem. The only reason for changing the CPD is if the cable feeding it is undersized.


Anyway, back to the original question. Yes you can wire the oven into a standard plug with 13A fuse. There will be isolation on the socket you plug it into and failing that it can always be pulled out of the socket if you needed to.

 

[IJWS15]

Appliances that are permanently connected should not use plugs.

Plugs rely on removal and insertion (wiping) to clean corrosion off the contacting surfaces, leaving an appliance plugged in for years can (Note: "can" not "will") cause corrosion build up at the contact surface. This can cause a poor connection and heat build up with highly rated appliances.

This is why some manufacturers say you should use a hard wired outlet rather than a plug.

 

[plugwash]

on the other hand i've heared manufacturers of washing machines and dishwashers often have repair staff who will refuse to work on units that are wired in.

 

[Brigman]

Thanks all. Very helpful.

 

[ColJack]

Can I use an existing cooker switch to feed 2 single unswitched sockets ( in 4mm² cable each from the cooker switch ) behind the cabinet next to the electric oven / gas hob for their connection?

I believe that the cable feeding the cooker switch is 10mm², but it is not marked and I am not certain.. ( I don't use 10mm² T+E at work, just tri-rated singles... )

I will downrate the breaker accordingly to a 32A or 20A ( switch will possibly have a socket, not decided yet )

 

[plugwash]

that sounds fine to me.

 

[securespark]

I will back Davy up: It is perfectly within regulation to have a 32A radial with a minimum of 4mm², providing it does not serve an area greater than 50m².

In effect, that is what a cooker circuit with a socket on the end of it is, 'cept it's usually 6 mil, not 4.

 

[breezer]

on the other hand i've heared manufacturers of washing machines and dishwashers often have repair staff who will refuse to work on units that are wired in.

That is true, since i was one such person

The reason is we have to do an insulation resistance test before and after working on the appliance.

you can't do that if it is fed from an fcu, which we were not insured to touch