Electricians - Advice!

[Gaygle]

Just looking for some advice from our fellow OcUK sparkies and/or DIY pr0s.

We currently have a single 2.3KW oven plugged in with a standard plug and 13A fuse and no local isolation rolleyes. We also have a 6KW hob on top which is hardwired in to a junction box of some kind behind the oven with a 6.0mm cable which does have a local isolation switch.

Now, we're wanting to get a new oven which is 3.4KW (so I obviously can't use a standard plug) and a new hob. The new hob should not be an issue, as there is already a nice 6.0mm connection/junction box for it. However, it will be a bit of an issue with the oven.

Now my amateur electrician mind is saying, if I get a sparky in, would they be able to somehow make the junction box feeding the hob, have two cables coming out of it so one will be able to feed the oven also? The local isolation switch would then obviously control both the oven and hob instead of just the hob. For info, the hob is on a dedicated "Cooker" circuit at the main fuse box, whereas the oven is part of the "Kitchen Sockets" circuit.

 

[Traffic_Warden]

What's the actual question?

You will need a 10mm2 cable if you intend on using both the oven and hob from the same connection unit.

The 6mm2 will need replacing with that, and possibly a new fuse/breaker to suit.

 

[ZG002]

It is possible to wire two 6mm cables into the cooker outlet yeah.

 

[Beer_MonsterUK]

http://www.alertelectrical.com/prod/1022/click-45a-dual-cooker-outlet-plate-prw217

Depending on how the cable is installed........clipped direct/buried in a wall/trunking then I'd make sure the protective device is around 32 or 40 amps.

Your total load is around 40amps ,but unless you are intending on turning every single element on for hours at the same time, you should be good. In the electrical game diversity is your friend.

In worst case sanario ,you trip your protective device on xmas day and then you have to call the sparky in to run a dedicated supply for the oven, but I'd be going for the dual outlet connection plate 1st.

It is possible to wire two 6mm cables into the cooker outlet yeah.

Take my word for it, it's nigh on impossible to connect 2 6mm's into a standard cooker connection unit and make a decent job.

What's the actual question?

You will need a 10mm2 cable if you intend on using both the oven and hob from the same connection unit.

The 6mm2 will need replacing with that, and possibly a new fuse/breaker to suit.

It doesn't matter what cable is used, so long as the protective device is suitable for the cable......hence my advice for a 32/40amp protective device depending on the installed cable reference method. The total load works out at 41amps (worst case senario, if everything is on at the same time, for an extended period of time, at which point thermostats are kicking in and out), then it's possible that the protective device will drop out, then it is time to call a sparky, but my advice is, the 1st port of call is to use the existing circuit and a dual cooker outlet and monitor the situation.

 

[ZG002]

A dual outlet is a good idea, but it's no where near impossible to wire into a normal outlet. Each to their own.

 

[Traffic_Warden]

http://www.alertelectrical.com/prod/1022/click-45a-dual-cooker-outlet-plate-prw217

Depending on how the cable is installed........clipped direct/buried in a wall/trunking then I'd make sure the protective device is around 32 or 40 amps.

Your total load is around 40amps ,but unless you are intending on turning every single element on for hours at the same time, you should be good. In the electrical game diversity is your friend.

In worst case sanario ,you trip your protective device on xmas day and then you have to call the sparky in to run a dedicated supply for the oven, but I'd be going for the dual outlet connection plate 1st.




Take my word for it, it's nigh on impossible to connect 2 6mm's into a standard cooker connection unit and make a decent job.



It doesn't matter what cable is used, so long as the protective device is suitable for the cable......hence my advice for a 32/40amp protective device depending on the installed cable reference method. The total load works out at 41amps (worst case senario, if everything is on at the same time, for an extended period of time, at which point thermostats are kicking in and out), then it's possible that the protective device will drop out, then it is time to call a sparky, but my advice is, the 1st port of call is to use the existing circuit and a dual cooker outlet and monitor the situation.

Yeeeehaaaaaaa Listen to the cowboy!

What's the power rating of the "new hob" or is it just a like for like replacement?

 

[Gaygle]

Thanks for all of the replies.

Would the dual outlet connection be suitable for both the oven and hob? Afterall, there is a possibility that the oven may well just be running on it's own and drawing a max of 14A yet it's connected to a 32A fuse at the MCB box. Is that ok? As far as i am aware, an oven is a fixed load device and therefore does not need a fused connection to deal with overload protection, but it does need one for fault protection - would the 32A fuse in the MCB be suitable for this fault protection?

The power rating of the new hob is 5.5KW-6.5KW. The oven is peak of 3400W (which I don't think it'll hit as every other oven in it's league is around 2600W-2900W max).

The electrician came round last night and he thought it'd be absolutely fine with diversity taken into consideration. He did some sums and called me back to confirm. With diversity and cookers/hobs i understand it's 100% of the first 10A, then 30% thereafter. The 6mm cable runs through the cavity in the wall (timber framed house).

With this applied to both appliances individually, it gives about 27A when diversity is TIC and that's only if all of 4 hobs and oven was on at the same time - which is very unlikely.

 

[JohnnyG]

If the cable from the outlet to the oven is 6mm or greater then a 32a breaker will be fine, but what hasn't been mentioned here or by your electrician it seems is the manufacturers instructions.
They are King nowadays and must be complied with by a professional installing anything or a DIYer if he doesn't want any problems down the line.
At a guess the MI's instructions will state that the oven must be protected by a 16/20a OCPB with at least 2.5mm cable, I'd check that before doing anything.

 

[C.R.A.Z.Y]

It is possible to wire two 6mm cables into the cooker outlet yeah.

Of course it's physically possible provided you use an outlet that has large enough terminals, however in my opinion it's a very poor choice as it will then have the inherent safety issue of a ring final!
Much better and safer to simply install another 6mm2 feed and have each appliance on it's own radial.

16/20a OCPB with at least 2.5mm cable,

What the heck is a OCPB It's been a few years since I studied this but I have never heard of the term OCPB? Is it just an acronym for maybe 'OverCurrentProtectiveBreaker' If so never seen that before :-/

Personally I won't install a kitchen appliance without RCD protection due to the higher fault risk due to the issue/hazards with liquids in a kitchen, splitload RCD or RCBO works for me

 

[Beer_MonsterUK]

Yeeeehaaaaaaa Listen to the cowboy

Nice sweeping statement.......

Depending on the reference method the cable can take "upto" 47amps, more than the design load of the oven & hob.

Granted, it would be better to install a new 4mm radial for the oven, but I'd be trying the dual outlet 1st.

would the 32A fuse in the MCB be suitable for this fault protection?

Fault protection depends on the type of protective device, BS3036 rewirable/cartridge fuse/MCB. Unless the earth fault loop impedance of your supply is high......or the cable run is exceedingly long I wouldn't have thought it would be a problem, but then again ,you're asking all the right questions, but not supplying enough information to give a definate answer. There wouldn't be a 32amp fuse in an MCB?. If you are unsure of any of the information, install a RCD for fault protection.

 

[JohnnyG]

What the heck is a OCPB It's been a few years since I studied this but I have never heard of the term OCPB? Is it just an acronym for maybe 'OverCurrentProtectiveBreaker' If so never seen that before :-/

It's a typo.
Replace B with D.

 

[Millwall.FC]

Joys of house bashers.

 

[Liampope]

it gives about 27A when diversity is TIC and that's only if all of 4 hobs and oven was on at the same time - which is very unlikely.

Either that's a little badly worded, or you're not understanding diversity fully. Taking diversity into account doesn't mean you'll actually only be drawing 27 A even if everything is on. Diversity is just a concept/philosophy that says you can design certain circuits for less than the potential maximum demand since it's unlikely the equipment will draw maximum demand for long enough. A bit like how a socket circuit isn't rated to allow a 13 A load plugged into every socket. If you really did have all your hobs and oven on max you'll be well over 27 A, but it's unlikely. Even if you were actually using all the hobs and oven at once, at least some are likely to be cycling on/off maintaining a chosen setting, so still unlikely to pull maximum load even using all the hobs/oven.

One thing about relying on diversity for your cooker circuit, is if the hob is induction, apparently some of them can be pretty good at cleverly distributing power, so they can draw max power even if you are not using all the hobs. Especially if they have a boost function. So whether it's a good idea to rely on diversity is a subject of debate.

I'd agree with Beer Monster that a simple dual outlet connection is likely your solution. At least worth trying and seeing if you get nuisance tripping. You probably wont. That is provided, as JohnnyG points out, the manufacturer's instructions for the appliances permit them to be protected by only a 32 A overcurrent device. Some appliances designed for Europe require overcurrent protection at 16 or 20 A, which practically means they need their own circuit. If your MIs don't say that, you are good to go with a dual outlet connection.

As also pointed out, depending on how this 6 mm^2 is installed, it may be permitted to change the 32 A device to a 40 A, and that you will never trip.