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"

 

[steveberry11]

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.

230 volts should always be used what happens when the the DNO changes the transformer trappings of carry out switching in the area.

Stick with 230v

 

[1shortcircuit]

"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"

Simple test and compare to max Zs for the protective device

 

[ExArmy]

230 volts should always be used what happens when the the DNO changes the transformer trappings of carry out switching in the area.

Stick with 230v

well they have been talking about it for a while, i suppose it might happen one day...

 

[edward cooper]

i know he has not done job yet. As i have treated it as fixed equipment then I would put it on its own circuit and then because i have done this it will require rcd protection. i do how ever think my post is pretty clear.

 

[spark 68]

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"

Point 1) is in App. 15 in the BGB and is a recommendation.

Point 2) would your 100mA RCD upfront not satisfy the disconnection time for the Zs (you don't say if it is TD or not), although that in itself contravenes Reg 314.

 

[Guest55]

230 volts should always be used what happens when the the DNO changes the transformer trappings of carry out switching in the area.

Stick with 230v

Thats not the guidance given in the IEE electricians design guide when making a detailed assessment.
But im too busy getting drunk to argue it out lol.
;-)

 

[edward cooper]

i was not stating i would not fit rcd i was just quoting what some one else stated. i believe that it needs rcd protecting. If you fit a 3.2kw cooker on the ring without 30ma rcd protection i think your a fool. Dont forget this is a TT system.

a kettle is not fixed equipment and there is no comparison to be made between a kettle that is on for 3 minutes and a cooker that maybe on for three or four hours possibly a lot longer

 

[ExArmy]

Simple test and compare to max Zs for the protective device

it's about 6ohms at the socket next to the cooker which i would spur off, so on a 3036 it would almost certainly not disconnect within 0.4 seconds. if that is the limit for TT? i must admit i've not done an awful lot with TT. yet

 

[sedgy34]

Either put cable in trunking and install a rcd spur if your that concerned

 

[edward cooper]

TT ExArmy disconnection is 0.2sec

 

[spark 68]

Ex Army,

Welcome to my world,

Where the client says it is only a little job....

When you get there, there is no main bonding, no RCD, no spare ways in the CU (usually a 3036 4 way board) and/or no CPC on the lighting circuit, and they want class I (from B&Q)lights fitting, and on it goes...

The upshot of this is a bloke down the pub does it anyway, lol

 

[edward cooper]

Very true Spark 68.

Its amazing how many different answers you get to the simplist questions too.

 

[Guest55]

If you fit a 3.2kw cooker on the ring without 30ma rcd protection i think your a fool. Why ? whats so dangerous about a cooker ?


Dont forget this is a TT system. Yes , and it has a upfront 100mA rcd , so what ?

a kettle is not fixed equipment and there is no comparison to be made between a kettle that is on for 3 minutes and a cooker that maybe on for three or four hours possibly a lot longer That true , no arguement there , but youre talking about the de-rating of a ring mains capacity , has no connection the issue of rcds.

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

 

[edward cooper]

Nothings dangerous with the cooker especially apart from the fact that its made from metal and if fault occurs its only a 30ma rcd or lower that protects life.

socket outlet circuits on a TT system must be protected by a residual current device with an operating current of 30 mA and as he wants to spur off the existing it needs rcd protection.

I dont want to argue im just saying that i would not fit this cooker without a 30ma RCD regardless of what obsure regulation you can find.i would also fit it on its own radial. i might be going over the top in your eyes but at least when i leave i know its safe

 

[ExArmy]

Ex Army,

Welcome to my world,

Where the client says it is only a little job....

When you get there, there is no main bonding, no RCD, no spare ways in the CU (usually a 3036 4 way board) and/or no CPC on the lighting circuit, and they want class I (from B&Q)lights fitting, and on it goes...

The upshot of this is a bloke down the pub does it anyway, lol

yep, i really can't be bothered with this one either. i'm back there at 9 in the morning, still havent decided what to do. i said this evening i'll have to RCD protect anything i fit which would mean changing the board, so i said i'd have to carry out an EICR first before i could price for the work, which is going to be ALOT as the board is the opposite side of the house to the stop cock and the gas meter and theres no bonding. and the house is a tip, and dirty.

 

[Strima]

the board is the opposite side of the house to the stop cock and the gas meter and theres no bonding. and the house is a tip, and dirty.

Didn't know you'd been round here, should have stayed for a brew...

 

[Guest55]

No bonding ??
lol , then youre not going to be doing any work till that sorted.
if i was you i'd just price mself out of the job , sounds a whole load of hassle unless the customer is gonna pay for all the extras.

 

[ExArmy]

so if i was to fit a new board, i'd have to fit a 100mA time delayed RDC main switch? also i would fit bonding, and what about the main earth to the erath spike? it's 10mm at the minute, dissapears into the wall and i can't see where it goes. how do i go about fettling this upto the 17th edition, and how do I test it?

 

[1shortcircuit]

No bonding ??
lol , then youre not going to be doing any work till that sorted.
if i was you i'd just price mself out of the job , sounds a whole load of hassle unless the customer is gonna pay for all the extras.

Have you weighed the client up yet? Judging a book by it's cover is never good (and sometimes it goes wrong) but is there money in it for you? Are they likely to go for it OR are could this be a factor as to how they ended up with a shoddy job done in the first place?

If in doubt price yourself out of it and walk away:thumbsup

 

[ExArmy]

No bonding ??
lol , then youre not going to be doing any work till that sorted.
if i was you i'd just price mself out of the job , sounds a whole load of hassle unless the customer is gonna pay for all the extras.

yeah thats looking like the option i'm leaning towards, i'll do the EICR and then whack in a sky high price...