in after a cowboy, cooker nearly burnt the house down!

[ExArmy]

I have just been to look at a job where i was asked to install a cooker as the previous one had nearly burned the house down apparently. when i took the cooker out there was a large burnt patch (300m accross), loads of charcoal, almost got through 1/2" ply below . when i pulled out the heat resistant flex i couldn't see where it had been plugged into, but it's likely it was plugged into the ring. it is a 3200W cooker from argos, the customer had got an argos technician out and apparently the cookers fine and it was down to the installation. customer reckons it was sat ontop of the connections and it was bodged up, I did try asking the customer to clarify how the cooker was connected up, but couldn't get much out of her! theres a 2.5 T&E running below the worktop behind the cupboards, not connected to anything but still live? but couldn't find where it came from as all the cupboards are full to the brim!

it's only a small house, 2 up 2 down, it's TT, got a 100mA RCD upfront and a 8 way 3036 board with 3 circuits (ring, lights and shower). ZE is 5-6ish ohms. would it be ok to spur it off the ring to a fused spur above the worktop, and then down to the cooker? an just put it on a minor works?
I'm not entirely sure what the line is about working on a circuit without 30ma RCD protection, do i need to add an RCD first or not?

also, the voltage is 250V at this house, 3200W at 250V is 12.8, so it i put a 13A fuse in the FCU then it will be alright? i seem to remember something from college saying all calculations to be worked out at 230V, in which case the current will be 13.9A and it will be more than the fuse rating. probably never blow, but what should i do here?

 

[Guest55]

230 volts is just the baseline for design calcs where supply details arent known.
If you know the actual voltage , in this case 250v , then use that value.

 

[Guest55]

Either way , a 13amp fuse should do it.

 

[spark 68]

You have Diversity too, 1st 10A + 30% of the remainder.
Works out about 11.2A @ 230V.

 

[sjm]

Any NEW sockets, or wiring that is concealed within the walls requires 30ma RCD. So if you use an FCU and your wiring is surface mount then I don't see a problem. The cooker will probably never pull full load anyway and 13.9 amps won't blow the 1361 fuse for ages. If you're worried use 4mm cable for the spur.

 

[jdd]

Pretty sure you should have a 30mA rcd protecting mate.

 

[Amp David]

That's one big burnt patch too. How big's the kitchen?

 

[jaresquire]

Just for future reference the power of the cooker is not constant but depends on the voltage, so the quick calcs are not valid. The figure quoted is probably at 230V.

 

[ExArmy]

erm i meant 300mm. so i don't need an RCD?

 

[Guest55]

erm i meant 300mm. so i don't need an RCD?

Yes , you do.
Any cable you install thats buried in the wall needs to be rcd protected , so if youre spurring off a socket for the cooker , then the ring needs a rcd.
Either that or surface fix cable.

 

[1shortcircuit]

erm i meant 300mm. so i don't need an RCD?

Are you going to be running a new circuit or altering/adding to an additional circuit?

 

[Guest55]

Edit : buried cable protection needs to be at 30mA , so the 100mA up front device isnt going to do it

 

[ClarkeTheSpark]

Anything new you do will want an RCD as a rule of thumb. Especially in a kitchen or bathroom as these are classed as 'special locations'

 

[RogertheBodger]

All final circuits on a TT system need to be be protected by 30mA RCD.

 

[1shortcircuit]

Do you see a pattern developing here?

 

[Guest55]

All final circuits on a TT system need to be be protected by 30mA RCD.

?? not according to page 28 of the current onsite guide.

 

[ExArmy]

?? not according to page 28 of the current onsite guide.

just looked that up, it seems to me that it's correct. unless they are installed in earthed steel conduit or earthed matallic sheath, all circuits must be protected by 30mA RCD.

 

[ExArmy]

Just for future reference the power of the cooker is not constant but depends on the voltage, so the quick calcs are not valid. The figure quoted is probably at 230V.

handy to know, so it's best to stick to 230V when working out calculations. makes sense when you think about it

 

[Guest55]

the very last sentance on that page says " the remainder of the installation would require protection by a 100mA rcd"

which implies not every circuit must need 30mA rcd for it to say that ??

not much gratitude there for walking you through your job exarmy ? :-/

 

[jaresquire]

The Onsite guide is an example of 'KISS' and is just a guide

 

[1shortcircuit]

the onsite guide is an example of 'kiss' and is just a guide

keep it simple stupid

 

[Guest55]

keep it simple stupid

not simple enough apparantly.
;-)

 

[1shortcircuit]

not simple enough apparantly.
;-)

Made me chuckle

 

[ExArmy]

the very last sentance on that page says " the remainder of the installation would require protection by a 100mA rcd"

which implies not every circuit must need 30mA rcd for it to say that ??

not much gratitude there for walking you through your job exarmy ? :-/

sorry if that came accross as me not showing gratitude, i am greatful for all input on this thread and wasn't arguing with you, but i just can't see how page 28/9 clearly lays out the requirements, to me it's consfusing! for a start it says "TT conduit installations". i've had a good poke about the house, not seen any conduit yet. so does that apply?

 

[Guest55]

It doesnt matter what sort of wiring the house has , even if it is in steel conduit or not.
Its only your work that has to be considered , so if you install a cable to your new cooker spur , that has to be 30mA rcd protected , which will mean fitting a rcd at the mains even though theres a 100mA rcd already there.
OR
Fit the new cable in surface trunking then you dont have to fit extra 30mA rcd.

 

[1shortcircuit]

It doesnt matter what sort of wiring the house has , even if it is in steel conduit or not.
Its only your work that has to be considered , so if you install a cable to your new cooker spur , that has to be 30mA rcd protected , which will mean fitting a rcd at the mains even though theres a 100mA rcd already there.
OR
Fit the new cable in surface trunking then you dont have to fit extra 30mA rcd.

I agree with surface mount otherwise you may find yourself having to work around discrimination issues.

 

[edward cooper]

Hi sorry to butt in,

As the cooker is classed as fixed equipment and is over 2kw shouldnt it be on a dedicated radial. Thats just my take on it so please dont shoot me.

Also as its now on its own dedicated radial it will need 30mA RCD protection because if you surface mount it it will look awful and you will get the name John Wayne.

 

[1shortcircuit]

As awful as surface mount is it does serve it's purpose and it's the easiest option for the homeowner to consider.

I think we have all probably installed surface mount at some stage or another? :thumbsup

 

[Guest55]

..................Thats just my take on it so please dont shoot me. Can someone get my gun.

Also as its now on its own dedicated radial Its not on any circuit - he hasnt done the job yet.

it will look awful and you will get the name John Wayne. The mans a legend.

.....................

 

[ExArmy]

is there something that says fixed equipment over 2KW has to be on a dedicated radial? it's just that i wouldn't know how to justify that to the customer, it's only 3.2KW, almost the same as a kettle!

and regarding surface mounting to avoid having to fit RCD, ihave just come accross Reg 411.5:

"cables installed on the surface do not specifically require RCD protection, however, RCD protection may be required for other reasons, for example, for the fault protection, where the earth fault loop impedance is such that the disconnection time for an overcurrent device cannot be met"