cooker & hob connection

[propertydev83]

We currently have a freestanding cooker which is wired with 6mm cable to a 45A mcb, but will soon be installing a separate hob and built under cooker (it is likely that they will either be 30A or 45A rated), and I needed some clarification on the correct mcb and wiring.

We also have a separate 45A cooker switch (with socket) installed with 6mm cable which is not currently connected to the consumer unit.

1) If the new cooker or hob requires 30A protection, can this still be wired to the 45A switch and then connected to the existing 45A mcb, or would the mcb need changing to a smaller one?

2) As the cooker and hob will be separate, can they still both be wired to the same terminal block, and then with a single cable to the cooker switch and mcb?

3) Also as the cooker and hob are separate, does this increase or affect the required protection from the mcb?

4) It states in the wiki here that cooker switches with a socket will require an upgrade of the level of protection. Does this mean that the mcb may need to be higher than 45A and the cable larger than 6mm?

Thanks in advance.

 

[AndyPRK]

I'm confused by your switches etc, But to try and answer your questions.

The MCB rating is there to protect the cable, so leave that alone.

1) Leave it as 45A so it can supply the maximum to both appliances

2) Yes. A dual outlet plate can help. (they do stick out a bit though, but ok if the outlet is to the side of the cooker)
http://www.ebay.co.uk/itm/Cooker-co...itchen_Ovens_Hobs_Cookers&hash=item35d8fc2301

3) No

4) I expect they mean it should have RCD protection, but as your not adding a socket, don't worry.

 

[ban-all-sheds]

4) I expect they mean it should have RCD protection, but as your not adding a socket, don't worry.

Unless any new cables buried in the walls are added.

 

[propertydev83]

Sorry for any confusion. The current cooker is powered by a single 6mm electrical cable running straight from the back of the cooker into the 45A mcb. When we get the new oven and hob the 6mm cable currently in use will be removed from the mcb.

The cooker switch mentioned is a 45A DP switch that has a socket on the plate with it and is fitted in the wall. This has (dead) 6mm cable running to electric cupboard and (dead) 6mm cable running to the space for the new cooker and hob. So when fitting the new appliances the current single cable will be removed and the new cables and switch are already in place.

1) Thanks. My confusion was with whether, say, a 30A appliance can be safely connected to a 45A circuit without it first being "fused down".

2) Great. Thanks.

3) Thanks.

4) Okay. It was the statement that "cooker switches with a socket are best avoided" when that is exactly what I have fitted which was the cause for concern.

 

[JohnW2]

1) Thanks. My confusion was with whether, say, a 30A appliance can be safely connected to a 45A circuit without it first being "fused down".

As has been said, from the point-of-view of an electrician, and of the regulations, the fuse/MCB is there to protect the cable, so provided the cable is OK for 45A (which 6mm² cable probably will be), that's fine from that point of view. However, if the manufacturer of the appliance stated that, say, the appliance should be protected by a fuse/MCB with a maximum rating of 30A/32A, then, strictly speaking, you are currently required (by regulations) to comply with that instruction.

Kind Regards, John

 

[AndyPRK]

Although within a couple of months? that will no longer be necessary.


It sounds like you have an odd setup, where by the old cable has a fault, and has been replaced with a new cable. Would you agree ?

That ebay link I gave you is designed to be screwed to an existing back box. It sounds like you don't have one for the current setup.
Should you wish to use it you would also need one of these :

http://www.ebay.co.uk/itm/moulded-b...al_Electrical_Fittings_MJ&hash=item5668d3afc6

 

[JohnW2]

Although within a couple of months? that will no longer be necessary.

Probably nearer 8 months than 2 - I think that Amd3 is going to be published on 1st January but not 'effective' until 1st July.

However, I'm not sure that it will, in practice, make all that much difference. Although the amended regs are expected (as per drafts) to give people more discretion as regards complying with MIs, the manufacturers will undoubtedly continue to state/threaten that failure to comply with their instructions will "invalidate the warranty" - which will probably put many/most people off exercising their discretion! If one wanted to contest the 'invalidation of warranty', I would imagine/hope that it would be possible to successfully argue (and 'convince a court') that many/most appliance failures could not possibly have resulted from an over-sized OPD, but many people will probably not want the potential hassle/cost of having to do that arguing!

Kind Regards, John

 

[Chris61]

1) Thanks. My confusion was with whether, say, a 30A appliance can be safely connected to a 45A circuit without it first being "fused down"

Just for reference, any fault on an appliance should not cause a device in the fixed wiring to operate. If there was a danger of such a thing occurring, the appliance should be adequately fused internally.

As already mentioned, over-current devices in fixed wiring are there only to protect the wiring.

 

[EFLImpudence]

Just for reference, any fault on an appliance should not cause a device in the fixed wiring to operate. If there was a danger of such a thing occurring, the appliance should be adequately fused internally.

For the benefit of the OP, that doesn't really make sense.
Perhaps:
any fault on an appliance should cause a device in the fixed wiring to operate. If there was a danger of such a thing damaging the appliance, the appliance should be adequately fused

As already mentioned, over-current devices in fixed wiring are there only to protect the wiring.

Yes.

 

[JohnW2]

Just for reference, any fault on an appliance should not cause a device in the fixed wiring to operate. If there was a danger of such a thing occurring, the appliance should be adequately fused internally.

For the benefit of the OP, that doesn't really make sense. ... Perhaps:
any fault on an appliance should cause a device in the fixed wiring to operate. If there was a danger of such a thing damaging the appliance, the appliance should be adequately fused

Indeed. I suspect that Chris did mean what he wrote, but I agree that, as written, it doesn't make a lot of sense. Indeed, even if the appliance were adequacy internally fused to protect itself, there would rarely, if ever, be any guarantee of discrimination between the internal fusing and the device protecting (the cable of) the circuit. I suspect that Chris was probably intending to just make the point that appliances should be internally fused to protect themselves, and should not rely on the device protecting (the cable of) the circuit to achieve that.

Kind Regards, John

 

[EFLImpudence]

I suspect that Chris was probably intending to just make the point that appliances should be internally fused to protect themselves, and should not rely on the device protecting (the cable of) the circuit to achieve that.

I agree and would think that, apart from extractor fans if that is the reason for 3A fuse requirement, they are.

Boilers, TVs, Some lamps (your definition ) etc.

 

[JohnW2]

I suspect that Chris was probably intending to just make the point that appliances should be internally fused to protect themselves, and should not rely on the device protecting (the cable of) the circuit to achieve that.

I agree and would think that, apart from extractor fans if that is the reason for 3A fuse requirement, they are. ... Boilers, TVs, Some lamps (your definition ) etc.

I'm not so sure it's all that common (to have internal fusing), particularly with higher-load appliances, is it? Many of those appliances may have thermal cut-outs, but that's a bit different.

Kind Regards, John

 

[EFLImpudence]

Well, yes but presumably they are not required.

I should have included 'when required'.

 

[JohnW2]

Well, yes but presumably they are not required. I should have included 'when required'.

Quite. It must be pretty rare (and would usually require one to hypothesise a very improbable fault) for the innards of a high-powered appliance not to be adequately protected by the OPD of the circuit supplying it.

Kind Regards, John

 

[propertydev83]

Sorry I have to ask and would like to know... why is it that some appliances are not externally or internally fused whereas a lot of others are? As far as I'm aware, every electrical appliance or fixture in this house does have an external fuse, except the lights (I'm pretty sure the boiler too has an FCU). I'm not really asking in the context of present regulations, but protection and the physics.

As has been said, from the point-of-view of an electrician, and of the regulations, the fuse/MCB is there to protect the cable, so provided the cable is OK for 45A (which 6mm² cable probably will be), that's fine from that point of view. However, if the manufacturer of the appliance stated that, say, the appliance should be protected by a fuse/MCB with a maximum rating of 30A/32A, then, strictly speaking, you are currently required (by regulations) to comply with that instruction.

Kind Regards, John

Thanks, John. Based on this information it's probably best if I try to find an oven and hob that have a matching "maximum" rating for protection from the MCB, otherwise I presume one would need to be fused down if they are on the same circuit.

It sounds like you have an odd setup, where by the old cable has a fault, and has been replaced with a new cable. Would you agree ?

That ebay link I gave you is designed to be screwed to an existing back box. It sounds like you don't have one for the current setup.
Should you wish to use it you would also need one of these :

http://www.ebay.co.uk/itm/moulded-b...rical_Fittings_MJ&hash=item5668d3afc6[/QUOTE]

The old cable is being replaced, yes. But there is no fault. It's simply that the old cooker is currently in a different location and the kitchen has also since been remodeled. As we had loads of spare cable it was easier to have the new cable fitted in place ready under the boards and through the walls without removing the current cable. The current cooker has also been moved around a lot and been used in different positions while works was being carried out so the cable was kept loose (not fitted in any walls or under floorboards).

(Of course, we could have fitted the cable under the floor and through the wall, and then extend it temporarily across from where it terminates in the space for the new cooker and over to wherever the old cooker needs to be with a lot of slack. But as we had loads of spare cable I didn't see any need...)

As for the terminal, yeah at the moment there is no backbox for that. If there will be enough space behind the new oven then I'll use one of the moulded boxes rather than hacking out a new hole for a backbox.