Ceramic Hob Trips Circuit Breaker

CBYR1983

Hi All,

This question probably asked a hundred times.

I have a built-in hotpoint ceramic hob and oven. The two are hard wired via junction box under the hob and then up to switch on the wall, connecting to circuit board on 32 amp breaker.

Note my lack of knowledge. Anyhow, the hob seems to have blown something, i.e. something popped. This has happened in the past but it seemed that it was only a light, I subsequentlyflicked the circuit breaker back and all the hobs worked.

However last night the hob blew again and it won't come back on without tripping.

I took it out - every time I flick the switch it blows and there is practically a puff of smoke coming from the connection plate on the hob (normally underneath of course).

So I've had to disconnect it so at least we can use the oven, have taped off the connections to the hob that I disconnected.

Has anyone any idea whether this could be a wiring fault or is the hob knackered? Does anyone know what parts would blow in these? My mate is a sparks (wired the house (though not the hob, that was kitchen fitter, it's in about 3 years), said omething about the "elements" going, reckons that the installation is sound (he probably would say that).

It's worked for 3 years, so would seem unusual that it would be a wiring issue.

Thanks in advance.

Buford T Justice

Think you've answered your own question OP. sounds to me like the unit is faulty

Not sure if they are serviceable though

2011

My mate is a sparks (wired the house (though not the hob, that was kitchen fitter, it's in about 3 years), said omething about the "elements" going, reckons that the installation is sound (he probably would say that).

First off don't get allow a kitchen fitter to wire anything beyond a plugtop. They are not qualified and it makes your completion certificate invalid which could have insurance implications.

Secondly using a junction box for a large load like that is bad practice.

My advice is to get your qualified electrician friend to have a look. I would guess that the terminations are melted at the hob or in the junction box.

Only use a qualified electrician for mains voltage electrical work or itcould cost you more than your home.

Good luck with it.

CBYR1983

@ 2011

Agreed, was not ideal allowing kitchen fitter to wire the hob/cooker.

What is best practice where there is a single feed to separate oven and hob? Why is junction box not suitable and what's alternative? Surely you wouldn't put the oven on the kitchen socket circuit...???


There's doesn't appear to be an issue at the junction box, but at the hob connection there are scorch marks on the wires.


My mate seemed to reckon that the wiring is fine, that the hob is the issue. On balance I would imagine this is right, on the basis that it worked fine for a long time, but I don't have the foggiest what way these hobs work, or what goes in them.

I can buy a new one, but I'm no millionaire.

2011

What is best practice where there is a single feed to separate oven and hob? Why is junction box not suitable and what's alternative? Surely you wouldn't put the oven on the kitchen socket circuit...???

Ceramic hobs are generally over 6kW and ovens are generally over 2kW. Therefore the current passing through the connection point can be large. Heat generated = (the square of the current) times the resistance. Therefore if the junction box has even a small resistance a large amount of heat can be generated. That is why it is better not to use a junction box.

The solution:
There are a few. Sometimes I would lug both cables and terminate them in the oven or the hob. That way you get a very solid connection using minimal space. Also I would use MK cooker switches that have terminals large enough for 2 x 6 sq. cables to fit in the load side. Other times I would wire both on seperate circuits. There is now a special junction box available for this purpose that is good but most people are unaware of it.

M cebee

2011 wrote: »

Ceramic hobs are generally over 6kW and ovens are generally over 2kW. Therefore the current passing through the connection point can be large. Heat generated = (the square of the current) times the resistance. Therefore if the junction box has even a small resistance a large amount of heat can be generated. That is why it is better not to use a junction box.

The solution:
There are a few. Sometimes I would lug both cables and terminate them in the oven or the hob. That way you get a very solid connection using minimal space. Also I would use MK cooker switches that have terminals large enough for 2 x 6 sq. cables to fit in the load side. Other times I would wire both on seperate circuits. There is now a special junction box available for this purpose that is good but most people are unaware of it.

sounds messy -nothing wrong with a decent JB

joints are not inherently dangerous

2011

I guess that depends on the quality of the joint. I agree that the proper cooker joint box is a good job but in my experience most people use a lighting type JB with 20A connectors. I somehow don't think that the kitchen fitter used the right type. Best of all is not to use one.

The simple truth is that every JB is a potential point of failure. The less JBs the better. I always try to avoid them as much as possible. I have seen too many melted ones. The solutions I have offered are very simple and effective IMHO.

M cebee

on the fixed wiring -best avoided

sparkies actually use lighting JB's for coookers

knighted_1

2011 wrote: »

First off don't get allow a kitchen fitter to wire anything beyond a plugtop. They are not qualified and it makes your completion certificate invalid which could have insurance implications.
.

hi sorry to go off topic but i have been telling a large company this for ages ,(something similar )

is there anything in legislation to back this up ,as in completion cert invalid and insurance being void ?

nearest i can find is part p in england and having to notify your local council if you wire something yourself but nothing over here

thanks

2011

knighted_1 wrote: »

hi sorry to go off topic but i have been telling a large company this for ages ,(something similar )

is there anything in legislation to back this up ,as in completion cert invalid and insurance being void ?

nearest i can find is part p in england and having to notify your local council if you wire something yourself but nothing over here

thanks

Phone RECI or the ECSSA

knighted_1

2011 wrote: »

Phone RECI or the ECSSA

they cant direct me to anything specific either

Buford T Justice

2011 wrote: »

I guess that depends on the quality of the joint. I agree that the proper cooker joint box is a good job but in my experience most people use a lighting type JB with 20A connectors. I somehow don't think that the kitchen fitter used the right type. Best of all is not to use one.

The simple truth is that every JB is a potential point of failure. The less JBs the better. I always try to avoid them as much as possible. I have seen too many melted ones. The solutions I have offered are very simple and effective IMHO.

I agree. Don't like using them myself, but I was forced to use one 60A JB on my cooker. Overkill maybe, but can never be too safe with electrical.

2011

Nothing wrong with overkill! It is so much better than a fire.

2011

Knighted: Be more specific. Ask them about sub system certificates. Ask about unregistered and unqualified people working on a certified electrical installation.

knighted_1

2011 wrote: »

Knighted: Be more specific. Ask them about sub system certificates. Ask about unregistered and unqualified people working on a certified electrical installation.

but is an elec cooker classed as a sub system ? and does it need to be certified ?

i have installed over the years and tested every cooker .ie voltage earth and insulation etc ,but am now being told not nessacary as any one can do it -now my understanding is different but cant find anything to back it up and as i said reci cant supply me with anything either ,

2011

but is an elec cooker classed as a sub system ? and does it need to be certified ?

Connecting a cooker to existing wiring would not require a cert.

Wiring a cooker circuit or installing a junction box to tap off an existing circuit would IMHO.

http://www.appliancesonline.co.uk/product_listings.aspx?fh_location=//catalog01/en_AOL/categories%3C%7Bcatalog01_36_37%7D/brandname=neff&action=clean&mNode=36&pNode=37

This little puppy draws nearly 29 amps at full whack.

Once a device draws a large current such as a ceramic hob I would advise people to use a qualified electrician.

knighted_1

yes this is what im getting at sorry -

if a cooker is rated 7.2kw or below it can go on a 32amp circuit no problem -

problem being that anything over that ,a 9 kw for example requires an upgrade in fuse to 45amp yes? or a 7kw hob and a 4.8kw double oven shouldnt be on a single 32amp circuit ?

joe soaps in companys at the moment are installing cookers with no knowledge of power ratings ,they just reconnect to the existing cabling without any safety checks or tests for 40 euros including vat

has to be something wrong yes?

this is why im looking for legislation or regulations but seems to be a grey area

knighted_1

s

M cebee

knighted_1 wrote: »

yes this is what im getting at sorry -

if a cooker is rated 7.2kw or below it can go on a 32amp circuit no problem -

problem being that anything over that ,a 9 kw for example requires an upgrade in fuse to 45amp yes? or a 7kw hob and a 4.8kw double oven shouldnt be on a single 32amp circuit ?

joe soaps in companys at the moment are installing cookers with no knowledge of power ratings ,they just reconnect to the existing cabling without any safety checks or tests for 40 euros including vat

has to be something wrong yes?

this is why im looking for legislation or regulations but seems to be a grey area

the first 10amp +30% of the remainder-i think that formula should be good
http://www.tlc-direct.co.uk/Book/6.5.2.htm

knighted_1

M cebee wrote: »

the first 10amp +30% of the remainder-i think that formula should be good
http://www.tlc-direct.co.uk/Book/6.5.2.htm

thanks for that makes sense now



32A MCB or 30A fuse
6mm flat Twin+Earth cable


Applying diversity:

9400w

9400/230 = 41Amps maximum

Formula: 10A + 30% of rest + 5A for any socket outlet

10 + 0.3 * 31 + 5 = 19.3A without socket outlet


so if i have a hob at 7.2kw add 4.2kw for double oven apply the formula

and i only need 22 amps

1140w/230 =49.5 amps

10 +0.3 *39 = 21.85 amps


thanks

CBYR1983

knighted_1 wrote: »

thanks for that makes sense now



32A MCB or 30A fuse
6mm flat Twin+Earth cable


Applying diversity:

9400w

9400/230 = 41Amps maximum

Formula: 10A + 30% of rest + 5A for any socket outlet

10 + 0.3 * 31 + 5 = 19.3A without socket outlet


so if i have a hob at 7.2kw add 4.2kw for double oven apply the formula

and i only need 22 amps

1140w/230 =49.5 amps

10 +0.3 *39 = 21.85 amps


thanks

So the 32A is ample - at least that re-assures - I bit the bullet and bought a new one - seems to be working fine.

Bruthal

M cebee wrote: »

sounds messy -nothing wrong with a decent JB

joints are not inherently dangerous

Yea id have to agree. A JB done properly is perfect. Using the current squared x resistance formula does`t mean much really because the JB resistance will be negligible if done right, and no higher than both hob and oven direct to cooker switch. Both hob and oven connected in JB or into cooker switch still more or less the same. The MCB board itself is a big JB so where does the current squared x resistance come in there?

Bruthal

knighted_1 wrote: »

thanks for that makes sense now



32A MCB or 30A fuse
6mm flat Twin+Earth cable


Applying diversity:

9400w

9400/230 = 41Amps maximum

Formula: 10A + 30% of rest + 5A for any socket outlet

10 + 0.3 * 31 + 5 = 19.3A without socket outlet


so if i have a hob at 7.2kw add 4.2kw for double oven apply the formula

and i only need 22 amps

1140w/230 =49.5 amps

10 +0.3 *39 = 21.85 amps


thanks

Applying diversity is well and good for averages over large installations or a housng estate because everything in every house will never be on, but a cooker could well have everything on at the same time although probably not often.

knighted_1

stick a clamp meter on and see total draw of power on full

knighted_1

robbie7730 wrote: »

Yea id have to agree. A JB done properly is perfect. Using the current squared x resistance formula does`t mean much really because the JB resistance will be negligible if done right, and no higher than both hob and oven direct to cooker switch. Both hob and oven connected in JB or into cooker switch still more or less the same. The MCB board itself is a big JB so where does the current squared x resistance come in there?

yes all new houses now have a 'juction box ' on the wall now

consumer unit to cooker switch ,cooker switch to wall plate (junction box)

if its an oven and hob combo most manufacturers want you to run separate cables from the jb to the oven and hob and not use the hob as a juction box for the oven or vice versa

has numerous benifits

lightnin

2011 wrote: »

.....using a junction box for a large load like that is bad practice.

Only use a qualified electrician for mains voltage electrical work or itcould cost you more than your home.

+1

M cebee wrote: »

sounds messy -nothing wrong with a decent JB
joints are not inherently dangerous

Have to agree again here with 2011, using junction boxes on largely loaded circuits is definitely bad practice. It maybe ok for JB's on lightly loaded circuits but even then i also try to avoid using them. Some of the older sparks that i worked with saw JB's as a definite no no and were thought of as too easy an option.

2011 wrote: »

......the simple truth is that every JB is a potential point of failure. The less JBs the better. I always try to avoid them as much as possible. I have seen too many melted ones.

+1


Anyway here's a great idea from Click(Polar Range), large terminals will easily take 10mm T&E in and two cable outlet, ideal for cooker and hob etc.

M cebee

accessible joints on appliances are fine if done properly-some people are using the wrong materials

i dont approve of JB's on 'fixed wiring' generally however

knighted_1

M cebee wrote: »

-some people are using the wrong materials

i

i said this earlier - two big appliance retailers are getting thier 'drivers' to install electric ovens hobs and cookers -they believe its just a matter of sticking three wires into the back of the new appliance and thats it -no safety checks no calculations on power rating no knowledge on anything -has to be wrong but apparently any one can do it

i have an email from one that says there drivers "arent qualified but they know what wires to use "

shouldnt be allowed

M cebee

surprising as it's not a job for an untrained person-

are they charging for it?

knighted_1

yes 40 euros , accident waiting to happen imo

M cebee

ya they're dumb but not dumb enough to do it for free