Wiring oven and hob - pics & questions

Maple77

Hello,

I'm replacing an oven and found that the old oven and the hob were both plugged in to the same connector terminal which is wired to the large red oven isolator switch







The wire plugged in goes to the hob and the one on the left was the old oven and was wired in here along with the hob.Both sets of wires in together.
Is it ok to do the same in wiring the new oven ??

The hob is rated 6600watts and the new oven is 2.5-3kw

Cheers

TheBody

You would be better off putting a cooker outlet on the wall. MUCH neater and safer than connectors like you have there. It's hard to tell from the picture but it looks like 2.5mm^2 feeding your cooker. Usually a 6mm^2 is used. You should probably upgrade this. Maybe there is a 6mm^2 to that isolator you talked about and you would only have to replace from there.

evosteo

thats 6 sq t+e, you can tell because its multi core copper and not single solid core,

+1 on the cooker outlet, be much neater looking

Maple77

Hello, cheers for replies.

The Fuse board / CU is rated 63A. The fuse for the oven switch says MBN 132A

Switch below is about 5m from CU


Cable from this switch to terminal block below is 6mm ( flat wire measuring 6.8 x 13.1 accross outer sheath) and travels 1m from switch above.

Two other wires are also 6mm and as said were both doubled up in this terminal block, The hob is rated 6600watts and the new oven is 2.5-3kw


So can I go ahead and wire it up as was ? Or is there a need for dual connector unit as ericmark has shown in pic above??

Thanks

meercat

Maple77 wrote: »

Hello, cheers for replies.

The Fuse board / CU is rated 63A. The fuse for the oven switch says MBN 132A

Switch below is about 5m from CU


Cable from this switch to terminal block below is 6mm ( flat wire measuring 6.8 x 13.1 accross outer sheath) and travels 1m from switch above.

Two other wires are also 6mm and as said were both doubled up in this terminal block, The hob is rated 6600watts and the new oven is 2.5-3kw


So can I go ahead and wire it up as was ? Or is there a need for dual connector unit as ericmark has shown in pic above??

Thanks

If possible replace the cable to the cooker switch
Put 2 x6mm twin and earth cables in
One to oven
One to hob

Connect both cables to load side of cooker switch

If not possible then
Use connector unit as in pic above

Maple77

Cheers meerkat,

Just to clarify , why two wires - one for hob one for oven - from load side of cooker switch , instead of two wires into the plastic terminal in pic above?

Is it because they'd probably be more secure - more room to fit two into each terminal ? Or is there any other reason.

Info really appreciate , cheers

TheBody

Hi, I'm still not convinced the cable you have there is 6mm squared. 6mm squared is not the dimensions of the outer sheath. It should looked like the image attached. Notice the way the cores of the cables are heavy and twisted. I think the cable you have in the image feeding your cooker is 2.5mm squared. It would have ONE SINGLE core for live, ONE SINGLE for neutral and ONE SINGLE for earth. If this is the case it will have to be upgraded to 6mm squared.

If it is not the case and you do indeed have a 6mm squared cable, I'd mount a cooker outlet on the wall behind the cooker (like the one I posted above). They are cheap. Then I'd connect the cooker and hob into that.

If you could post a picture of the fuse board and point out the mcb for the cooker that would be helpful.

meercat

only for handiness sake
that way there are only 2 cables into each terminal(cooker switch)
rather than 3 cables into cooker terminal box(feed in ,cable oven,cable hob)
you will also get a better connection especially if there are 2 tightening screws on each terminal

Maple77

Cheers merecat and theBody,

I've had a look at terminals on cooker switch and theres not really any more room to fit a second wire in on load side than on plastic connector so I think I'll check the plastic connector box in picture and go with that if it'll fit in securely.

Heres close up of cable theBody , not great pic but is same as pic you posted




TheBody - unit you posted would certainly be neater , but if the two 6mm fit into plastic connector box , securely , whats the difference?

Cheers

TheBody

That's a 6mm square cable so your fine. The connectors that are there will work but they would not be good enough to pass electrical regulations. If you do decide to use the connectors, maybe get a jobo box (see attachment) to protect the connectors. They are cheap and readily available in any electrical wholesalers.

Maple77

Cheers lads , great help, I've just connected one of the 6mm to terminals on back of oven - Belling single oven - really tight fit - not sure they're meant for 6mm. Have you come accross this , is this normal?

Thanks

meercat

Maple77 wrote: »

Cheers lads , great help, I've just connected one of the 6mm to terminals on back of oven - Belling single oven - really tight fit - not sure they're meant for 6mm. Have you come accross this , is this normal?

Thanks

"The hob is rated 6600watts and the new oven is 2.5-3kw"
just read your first post again

3x2.5 heat resistant flex would probably do a better job alright
some ovens come prewired with flex attached
maybe replace the 6square with that as you will get a better connection in oven terminal block

TheBody

Often happens that cables are a tight fit on appliances, light fittings etc. Guess it keeps costs down for manufacturers.

Do I get a free dinner from the new cooker for the advice?;)

knighted_1

meercat wrote: »

3x2.5 heat resistant flex would probably do a better job alright
some ovens come prewired with flex attached
maybe replace the 6square with that as you will get a better connection in oven terminal block

2.5 will not do - even though appliances are getting lower power wise and most consume less than 14 amps on full blast , it still must have 6sq for the earth - cooker circuit is not on the rcd side so to prevent possible electrocution earths have to be 6 sq -

evosteo

call me mad but the earth conductor in 6mm2 T+E is actually 2.5mm2 and as far as i know thats the reason its refered to as TWIN (same sized conductors L+N) + EARTH (usually a size smaller than the conductors)

The earth is to provide protection for the cable and device and to some extent you as well. If an earth fault occurs (live connects to the earth) then the current will flow from the live wire through the earth and back to the source and this should be an easier return path than from the live wire, through you, your shoes, the concrete you stand on, the ground, and then back to the source. So the earth wire should provide an easier return path. The earth should be connected to any metal parts where you are likely to touch them.

With this easier return path the current is quite large - it should be large enough to trip the circuit breaker or blow the fuse (2 or 3 times the rated capacity of the circuit and it will break the circuit within a short period of time). This large current breaking the circuit protection will heat up the conductors, however because it is only there for less than a second the circuit and devices are protected from heat damage (and subsequent fires).

The smaller diameter is OK because the earth wire current flows through it for a short period of time and although it will heat up more than the other wires, the protection will stop the current before this heat becomes a hazard.

knighted_1

cookers have a natural or acceptable earth leakage through the moisture levels in the elements - this can be up to 45 ma hence why it's not on the rcd ( 30 ma )
as 10 ma is the maximum let go this could kill
the human body's resistance is between 1500 and 3000 ohms - to ensure a defiantly better path to earth 6sq must be used -
if your waiting on a fuse or circuit breaker to protect you on 32amp cooker circuit chances are you will be seriously injured or dead before the breaker trips

M cebee

:pac::pac::pac:

evosteo

knighted_1 wrote: »

cookers have a natural or acceptable earth leakage through the moisture levels in the elements - this can be up to 45 ma hence why it's not on the rcd ( 30 ma )
as 10 ma is the maximum let go this could kill
the human body's resistance is between 1500 and 3000 ohms - to ensure a defiantly better path to earth 6sq must be used -
if your waiting on a fuse or circuit breaker to protect you on 32amp cooker circuit chances are you will be seriously injured or dead before the breaker trips

what im saying to you is the earth conductor in a 6sq t+e is 2.5sq and not 6sq like the live and neutral.

so if that is the case then there is alot of dangerous cooker set ups around the country

dazed+confused

I know this isn't a huge job and we're all trying to help each other out while saving a few pound at the same time, but this reminds me of what happened yesterday.

I was called into my nextdoor neighbours' house to help him out. The guy that Powercity had sent out (not an electrician!) to install his cooker was totally clueless as to why the new cooker wasn't working (the contacts in the cooker switch were knackered and I read 48V at the cooker terminals.) It just made me think that some jobs really are best left to qualified professionals. There were just so many other little things that could have gone wrong and this guy would never have noticed.

I have a go at a few plumbing jobs myself. But if plumbing DIY goes wrong its an expensive mistake. If electrical DIY goes wrong then somebody dies.

knighted_1

your right - I am in dispute with an electrical retailer that I supplied professional service to - they now have untrained and unskilled people doing cooker installs - not a clue to the dangers but there is nobody there to stop them -
so many cooker set ups are wrong and dangerous it's unreal -

Maple77

Knighted 1 ,

I have used 6sq, but the terminals on the new Belling oven were definitely not suited to this size cable, there is no mention in appliance manual as to recommended gauge for cable, whats the story here, are most people connecting them to a standard plug ?

evosteo

knighted_1 wrote: »

your right - I am in dispute with an electrical retailer that I supplied professional service to - they now have untrained and unskilled people doing cooker installs - not a clue to the dangers but there is nobody there to stop them -
so many cooker set ups are wrong and dangerous it's unreal -

what about the 6mm sq T+E run back to the board??????????

knighted_1

Maple77 wrote: »

Knighted 1 ,

I have used 6sq, but the terminals on the new Belling oven were definitely not suited to this size cable, there is no mention in appliance manual as to recommended gauge for cable, whats the story here, are most people connecting them to a standard plug ?

terminate them with lugs - belling oven is very tight

knighted_1

evosteo wrote: »

what about the 6mm sq T+E run back to the board??????????

what about it ??? 6 sq is the standard , (sometimes10sq)

evosteo

knighted_1 wrote: »

what about it ??? 6 sq is the standard , (sometimes10sq)

its a 2.5mmsq earth back to the board inside it

Solair

Actually, most modern ovens and hobs will not trip an RCD. It's a bit of an anachronistic regulation that seems to allow non-RCD protected ovens and hobs.

It was more of an issue with the old coil rings on hobs, which took a lot of abuse.

I really cannot see why the regulations do not require a RCBO on them at this stage.

It's quite common on the continent, in France anyway, to have a 30mA RCD on the oven and hob.

The other worrying problem that I have seen is that many ovens now ship with a flex pre-attached. These are quite regularly being directly connected to 32A (or higher) rated traditional Irish (or British) cooker circuits when they are designed for connection to 20amp continental radial circuits or even to be plugged into a 16 amp continental socket.

Should there be a short circuit, the flex is going to burst into flames as the MCB won't trip until there's a pretty high fault load (more than the pre-wired flex can withstand)

If the installation is carried out properly, both the oven an hob should have appropriately rated fuses / MCBs for their respective loads and a local isolating switch should be provided.

OP: You need to, at the very least, use a proper junction box (with the correct rating) to connect two heavy appliances to a single incoming cable. Using a 'chockblock' / strip connector to connect two appliances like that is not what those connectors are designed to do.

Cookers draw a LOT of current and if you have any kind of loose connections or connections that are not making good contact, you risk overheating and fire. It is absolutely vital that you make ALL cooker connections very securely and ensure that there is really good contact between the live parts.

One dodgy connection can = house fire.

M cebee

and the uk

knighted_1

Solair wrote: »

Actually, most modern ovens and hobs will not trip an RCD. It's a bit of an anachronistic regulation that seems to allow non-RCD protected ovens and hobs.

It was more of an issue with the old coil rings on hobs, which took a lot of abuse.

fire.

the fan elements and grill elements are still made the same as the old coil rings - it's the White power in them ( name escapes me ) that can cause earth leakage - higher end makers seal them much better nowadays and I've seen some cookers work fine on an rcd -

when you consider it's the second highest power source in your house, that there would be stronger regulation regarding fitting them - in the uk it's semi controlled by local building regs

M cebee

what's all that nonsense about the 6sq earth and people getting electrocuted

t&e has a smaller cpc

Bruthal

knighted_1 wrote: »

cookers have a natural or acceptable earth leakage through the moisture levels in the elements - this can be up to 45 ma hence why it's not on the rcd ( 30 ma )
as 10 ma is the maximum let go this could kill
the human body's resistance is between 1500 and 3000 ohms - to ensure a defiantly better path to earth 6sq must be used -
if your waiting on a fuse or circuit breaker to protect you on 32amp cooker circuit chances are you will be seriously injured or dead before the breaker trips

If you are in contact between the cooker live and its earth, an MCB of 0.1 amps wont trip, let alone a 32 amp one.

Bruthal

Solair wrote: »

Actually, most modern ovens and hobs will not trip an RCD. It's a bit of an anachronistic regulation that seems to allow non-RCD protected ovens and hobs.

It was more of an issue with the old coil rings on hobs, which took a lot of abuse.

I really cannot see why the regulations do not require a RCBO on them at this stage.

It's quite common on the continent, in France anyway, to have a 30mA RCD on the oven and hob.

Surprised at that myself at this stage.

The other worrying problem that I have seen is that many ovens now ship with a flex pre-attached. These are quite regularly being directly connected to 32A (or higher) rated traditional Irish (or British) cooker circuits when they are designed for connection to 20amp continental radial circuits or even to be plugged into a 16 amp continental socket.

Should there be a short circuit, the flex is going to burst into flames as the MCB won't trip until there's a pretty high fault load (more than the pre-wired flex can withstand)

There is a risk, but the flex is unlikely to burst into flames on short circuit. If there is a short on it in the flex itself with a 32amp MCB as the first upstream protection, the likely outcome is the MCB will trip, or the short will be blown clear if its a couple of them very light strands shorting.

Dont forget, the internal wiring of cookers is small 2.5 single core wiring as well. We know they are inside a steel frame which helps prevent fire risks, but shorts still trip the 32 amp breaker. A 2.5 conductor can take well above the 32 amps for brief periods such as in a short circuit, and we would hope for an MCB to operate quickly in this event. Cables are rated for their continous current capacity, and this is above 20 amps for a 2.5 conductor.

It is far from ideal with a 2.5 flex and 32 amp MCB as the protection though.