Hi, We've just moved into a property and are replacing the single oven that was dead upon first use. The replacement oven is a 2.9KW unit requiring 16A hard-wiring. The oven we're replacing is connected to a 32A MCB via a double pole switch, with a 6mm T&E coming from that hard wired to the oven. There's also a plug socket which runs off the cooker switch that the gas hob plugs into (unsure of fuse size of gas hob plug). I know next to nothing about electrics, but just wondered if this sounds safe as a set-up? (and therefore if it's okay to simply replace the existing single oven with the new one without making any changes?) I guess I was wondering if there is any danger caused by having a 16A oven wired to a 32A MCB? Wouldn't that theoretically mean that if the oven malfunctioned it could draw up to double its power requirements before the circuit tripped? And could that therefore be dangerous? (or is it that the 6mm T&E can handle 11KW which is plenty as the circuit would trip way before this meaning no danger of the cable burning out?) Apologies if this is very basic, as I say though I know nothing about electrics, hence I wanted to run it past you good chaps. Thanks for any advice you can give.
Hi. The circuit breaker is to protect the cable not the appliance on the end of it. For someone who knows nothing you seem to know what cable size, overload protection and double pole switching is
I've been doing a bit of reading. Okay, so it should all be okay as the cable can handle way beyond 32A?
I see! That is the bottom line yes. Assuming it is 6mm (out of curiosity how did you determine that), doesnt need de rating due to installation method or a million miles from the consumer unit
I'm pretty sure it's 6mm.... says '6.0' on the cable and has an earth with two thick, multi-stranded cables for the live and neutral. I'm going to measure it, and buy a short piece and a piece of 2.5mm from the local DIY shop just to be sure. From what I have read though, multi-strand 2.5mm is fairly rare?
Hi GSte. The cable being multi-stranded means it's chust a bit older than modern cable (which, as you clearly know, is single strand). Your current setup is fine to use as it is, although if you were pedantic you could swap the 32A MCB for a 20A one. In the extremely unlikely event that your oven or circuit develops a fault that causes no more than a 20A draw, the smaller MCB will trip whereas the current one wouldn't. But I can't think of a realistic fault that would cause that . I don't understand why you would buy a piece of 2.5T&E? Is it chust to confirm the size of the '6mm' cable? If so, don't bother. If the existing setup coped with the old single oven, it'll cope with the new one. And, yes, your cable is almost certainly 6mm, which is good news.
Thanks a lot for the advice and info both of you. I had thought of replacing the MCB with a smaller one Devil's Advocate, but when I looked at the consumer unit yesterday I wasn't quite sure what I was doing so thought it best to leave it! It looked like each circuit was wired into their respective MCB, presumably you just unscrew and disconnect the wire then the MCB snaps out somehow? If I were to do this, would turning off the main switch on the consumer unit isolate all of the power to it, or would I need to do that elsewhere first?
Think about if it's OK running a 10 Watt LED lamp (which draws about 0.06 Amps) from the 6 Amp MCB on your lighting circuit... Or hanging a weight of 100kg from a piece of rope with a breaking strain of 200kg.
I get the analogy, if I could get a 6mm into a batton lampholder then I would be quite happy running it straight to a 32A MCB. However I have reservations about all the wires and stuff inside the oven itself, rating of the selector switch contacts etc. Maybe something goes wrong with the switch and both the grill element and oven element start operating at once, this would probably trip the 16A breaker but not a 32A so instead all the wires melt inside the oven. Having said that, if you take the back off a double oven most of the wires inside that are just as thin, likewise with a shower.
Each of those wires only takes part of the load. Not the full load. Each element is wired back to the central bus. Each control group is wired back to the central bus. Bit like all the circuits in a house going back to a CU. Those wires won't melt.
The analogy was lost on me initially, but the following debate is interesting and I think I follow it. Well there I was thinking that it was going to be a simple job of wiring the 6mm cable directly into the oven..... So the oven arrived today and it seems that I can't wire the cable straight in. It has come with its own cable, with a kettle lead type end that plugs into the oven, and then three bare wires on the other end. The cable itself is only 1.5mm! Which I think I'm right in saying can handle up to 15A? Please can someone advise on what to do now? I'm not sure about: a) how to connect this to the power supply/existing cable (can I crimp them together somehow? Or would I have to wire it directly into the double pole switch? Which is pretty much impossible without destroying the kitchen....) b) do I now need to attach this cable to a lower rated MCB / fused switch to prevent the supplied 1.5mm cable melting?
So you have a 6mm cable from the CU with 32A MCB going to a a Cooker Unit with a 13A socket included in the unit. And a 6mm cable from the Cooker Unit running to a cooker connection unit under the worktop. You can go a couple of ways with this (1 run a 2.5 T&E cable from the cooker connection unit under the worktop to a Double Socket Outlet under the work top and plug in both the hob and oven. (2 Instead of a double socket use 2 FCU's and connect the hob to 1 FCU and the oven to the other (3 replace the Cooker Connection Unit with a double Cooker connection unit that allows 2 appliances to be connected to the unit. Option 1 or 2 will allow you to keep the 32A MCB in the Consumer Unit because each appliance will be fused. Option 3 Will require the 32A MCB to be replaced with a 20A MCB
GSte, can you clarify fully, please: the existing 6mm 'loose' cable that used to go in to the old oven, where does the other end go to? Does it disappear into the wall, buried in plaster, behind the where the oven used to be? Or does it go to a proper cooker outlet like this: http://www.screwfix.com/p/lap-1-gang-45a-cooker-outlet-plate-white/61074 (AND - important - this 6mm 'looses' cable, is it normal flat T&E cable or a round black flex? ) If it simply disappears into the wall and makes its buried way up to the cooker control switch, then you should fit one of these 'outlets' I linked to above. Ideally locate it close to where the existing cable comes out of the wall, but make sure that it won't be in the way of the oven's back. To fit it, you'll also need a metal back-box of at least 35mm depth (the 47mm box is best*, although you may get away with the shallower box but fit it slightly deeper in the wall - say around 40mm+...) and then you run the existing cable to that box. Channel a slot in the wall for the cable to run to this box if necessary, make sure you leave a good amount of spare wire ends inside the box to enable easy connection to the front plate, and then plaster the cable in. Your new oven's cable now wires correctly into this outlet plate. What's your wall made of? If it's plaster over block, then you may need an SDS drill (working as a chisel) to make this hole. Don't worry if it's rough - just fill in with a patching plaster around the back box when it's fitted. The hob electrics - can you explain how this is currently wired in? * http://www.screwfix.com/p/appleby-galvanised-steel-knockout-box-1g-47mm/90698 Don't forget a rubber grommet...
You can obtain surface mounting boxes for cooker connection points. Stick out quite a bit, but often cookers have voids which would allow a surface box to protrude without hitting the cooker.
Many thanks for these replies chaps, they're extremely helpful. Just to explain the setup further, I have: 32A MCB in consumer unit, going to a 45A Cooker Unit with a 13A socket included in the unit. Then a 6mm cable from the Cooker Unit running to a cooker connection unit under the worktop. Then from this there is a 6mm twin and earth which was wired directly into the old oven, and a 2.5mm twin and earth going to a single surface-mounted power outlet that the gas hob is plugged into. Here are some pictures to clarify: An additional problem is that the new oven cannot fit flush under the worktop with that surface mounted plug socket, as it protrudes too far from the wall. From what you're all saying it sounds like the simplest option would be not to use the 6mm cable that is still there, but rather to remove the single plug outlet, channel a twin one into the wall and connect the 2.5mm twin and earth to it, then plug both hob and oven in, as their own fuses will then protect them and I won't have to fiddle about with the consumer unit?
Forums
Facebook
Twitter
You Tube
Instagram
Shop