Powering two cookers off single radial electrical circuit

Page 1 of 2  
Hi all
Is it possible to power a single oven and a combination microwave/oven off an existing single radial (I presume) circuit (currently powering a double oven)? Both appliances have a max power rating of 3.6 kW (or 3.6kW and 3.7kW). I make it that each would draw 15A max, so both together would draw 30A max; would this work using the existing radial circuit? Bearing in mind also that the single oven will be moved to the other side of the kitchen (approx 2.5m) from the existing double oven, so a feed will need to be taken across there, with the combi oven on the side of the existing double oven. There will also be a fridge on the combi oven side, and we would need a double socket outlet for general purpose. How would this be wired up? Would the ovens be individually fused?
An electrician I had around yesterday said he could get away without using the existing double oven electricl circuit for the new single oven on the other side of the kitchen, using the ring circuit on that side in some way... would this be possible / safe? From my research, this is not possible.
Many many thanks!! Michael Brewer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

This might be of help:
http://www.diynot.com/pages/el/el027.php
--
http://www.basecuritysystems.no-ip.com

Outgoing mail is certified Virus Free.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I did find that useful, but first it says "As a general rule an electric cooker will require its own radial circuit. This means it requires a direct connection to the consumer unit with its own fuse way there". Then it says "A 30amp fuseway can support an appliance of up to 7.2kw providing that the control unit does not also have a socket outlet". What I need to know is whether I can treat my two cookers as a single appliance and feed them both off the existing radial circuit; the total load is 7.2kW, which places it within this stated limit. I'm a complete novice, but I can't see the difference between powering a double oven (which is just two ovens in a single unit) and powering two separate ovens from a single radial circuit, providing the max loads are equivalent. If it is possible, how would the two ovens be wired to the radial circuit? Just like any other multi-point radial? Does it make a difference that the two ovens are separated by approx 2.5m?
Many thanks for your help!! Michael Brewer

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

--
http://www.basecuritysystems.no-ip.com

Outgoing mail is certified Virus Free.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
My guess is that your microwave "combi oven" comes with a standard 3-pin plug. If this is the case then the best choice is probably to just plug it it to a socket - that's they way they are normally designed to be used.
--
http://www.mxf.info - information for developers of mxf systems

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
That would certainly simplify things; although the spec suggests it is just as hefty as, if not more hefty than, the single oven (3.7kW max for the combi oven; 3.6kW max for the single oven). By my reckoning that is 15A.
Thanks.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Can you not have a separate switch for each; one on one side of the kitchen near the mwave/oven, the other on the other side near the oven, both from the same radial circuit? Forgive my complete ignorance if this is the most idiotic suggestion ever made on this newsgroup !
Coming back to a related aspect of my original post, is it at all possible to power the single oven (3.6kW; 15A) off the ring circuit? I'm guessing the "diversity" calculation I've read about only applies to estimating the likely max load for a number of separate ring loads, but for the oven "max 15A" really does mean that it's going to draw 15A when you have it on the most power-intensive mode?
Thanks.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

more or less this exact subject about three weeks ago. Roughly summarising and applying to your enquiry: first, it would not be best practice to run your single oven off the kitchen ring. Even if you have a ring dedicated to the kitchen, it's prolly got two or three heavy loads on it (dishwash, washmosh, tumblebumble) and a few more intermittent 1-2kW loads (toaster, kettle). "Preloading" that ring with an oven (when it's on and its thermostat is calling for heat, it's pulling the 15A specified) is not the best of ideas. (I put it no more strongly than that: depending on how your particular household runs, it could be anything from definitely stupid (say there's 6 of you, serious amounts of cooking and washing going on espepercially at particular times of day) to entirely fine (one or two members, appliances used lightly and rarely at the same time, etc.) But on balance, and allowing for future occupants, it's distinctly better to use a dedicated higher-current circuit (or two) for your electric cooking needs. Diversity, as the Regs, On-Site Guide, decent books and so on all stress, is a "what's sensible in practice" notion which needs to be applied with relevant knowledge of how the circuit's going to be used in practice, and in the absence of detailed usage knowledge one should err on the side of caution.
Your existing radial would be a good and proper circuit to feed both appliances. I'm rather assuming the single oven is a built-in job which really truly will be used as a conventional oven quite often, pulling its rated 3.6kW: this makes powering it off a 13A plug and socket less than a brilliant idea (13A plugs aren't that great for continual loads at their full rating). Depending on the physical layout of your kitchen, it's OK to have either a single place where separate isolators (switches) for each appliance are located, or to have the isolators closer to each appliance. There's a requirement that these isolators be within 2m of the appliance they control.
In your case, you can provide the isolation for each appliance using any of: 20A double-pole switches (with neon indicators if you like), cooker-control switches (usually rated at 45A, and possibly physically bigger than you want), or fused-connection-units with a 13A fuse: but these last are kinda marginal, with the 13A fuse rating telling you they're specced for a nominal 3.12kW. If you use a decent brand (MK, Crabtree) they should be just fine, especially as your appliances won't be pulling their full rated power most of the time (as their thermostats cut in and out, etc.), but I wouldn't use that no-brand cheapie you found at the bottom of the bargain bin ;-)
The argument we had a few weeks back were about the guage of cable you could use for the final leg of the feed once you've split the radial into two for the two appliances. After some marginally ill-tempered discussion, we more or less agreed that 2.5mmsq is OK in most cases, 4mmsq would avoid doubt for any split-level use, and 6mmsq preserves maximum flexibility for either of the exit positions being usable in future for a single all-in hefty-cooker. (Balanced against the thicker sizes is the awkwardness of working with them: you want nice deep back boxes (47mm) if possible, though 4mmsq isn't too much of a pain). It also depends *critically* on how your radial's laid out: if the two isolators are daisy-chained, i.e. a single cable runs first to one of them, with the first appliance connected to the load terminals, while a second cable runs from the incoming-mains side of the first to the incoming-mains terminals of the second isolator, *only* that second cable can be reduced in size from the radial feed, since the first one is supplying both appliances.
Hope that helps - Stefek though your The argument we had was all about the thickness of
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 25 Jan 2004 21:21:07 +0000, stefek.zab wrote:

Also ISTR that for fixed cooking appliances then diversity calcs can be applied when considering the load for the circuit. A 'standard' 6 knob cooker can certainly pull more than the 32A circuit they are usually supplied from but in fact a 32A radial circuit is deemed to be able to supply a 6-knob cooker and ONE 13A socket. IIRC the first cooking appliance is rated at 100% and the second at 30% [A] so there should be enough capacity for a 32A radial to run both appiances and a socket and the fridge on the one circut.
[A] I the domestic environment (in a hotel it would be different IIRC.)
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 25 Jan 2004 21:21:07 GMT, snipped-for-privacy@hp.com wrote:

dedicated radial circuit.

not on a 30A circuit though.

If by marginal you mean underrated.

Maybe you did, still not quite right. At least, not if you're a pro.

20A radials, with 4mm cable, into 20A switches. Saves any confusion at all then.
SJW A.C.S. Ltd.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Why not?
If the 3.6kW is a maximum load, then the switch won't be asked to break more than 15A. I suppose you could argue that "nature of the load" arguments don't apply to microwaves.
OTOH, I'd probably just install a 45A DP switch anyway.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

in most cases", on reflection.
Which part of the reasoning did you have a concrete counterargument to? You seem to insist on applying the safe rule-of-thumb that every circuit element ought to be rated at or above the nominal rating of the circuit protection device. It's a *safe* rule of thumb, agreed: but one which can lead sometimes to excessive cost, inconvenience, or ugliness. In this case 20A-rated switches *are* adequately rated: the downstream loads each draw (well) under 20A, and can't cause an overload; while their short-circuit rating is considerably higher than 20A or 30A or 45A. As when this came up last, despite detailed working separating out the overload protection function from the short-circuit one, and the factual instances where that rule-of-thumb is not applied (rating of an appliance's internal wiring and switches, the design of a ring circuit itself where the 2.5mmsq in an unfused spur can't carry the 32A of the MCB rating, the Continental practice of using (suitably short) lengths of 0.75mmsq flex on appliances whose nature means they can't cause an overload plugged unfused into 16A Schucko-socket radials, and similar), you continue to insist that As A Pro, you have superior insight into what constitutes acceptable design.
Bluster like that just won't cut it. It's more useful to us in uk.d-i-y to have the *reasoning* and *principles* of safe working in the various trades examined and argued over, than ex cathedra pronouncements asserting an opinion, however well-founded that opinion might or might not be. The previous discussion showed in gory detail that 2.5mmsq could in many cases safely supply the final feed to separate 20A-25A appliances, while agreeing that it was marginal, under spec in the case of higher ambient temps, penny-pinching, and left you with little flexibility or safety margin. (All in all, just what you'd expect in a mass-market new build ;-)
Stefek
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Stefek and others: many thanks for taking the time to provide very helpful information.
I have a couple of final (dumb) questions related to my installation:
1) You and others have mentioned that the regs say that the control switch for an appliance must be within 2m of that appliance. Do the regs say whether the control switch must be above the counter (i.e. instantly accessible) or is it OK to have them out of sight under the counter, but still accessible through a cupboard?
2) A couple of remaining questions with domestic wiring that are troubling me are as follows. A ring circuit is usually wired with 2.5mmsq cable (rating < 30A), but is apparently able to provide up to 30A... is this because it's a ring not a radial and so current to any point can go both directions and is therefore split in half, so that a ring supplying 30A to a particular point would actually only be carrying 15A in the supply cables? This brings me to the question: why are cooker circuits provided as 6mmsq radials and not (e.g.) 2.5mmsq rings, if the latter will take just as much loading as the former?
Many thanks. Michael Brewer
snipped-for-privacy@hp.com wrote in message wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Because it is easier and neater to run one 6mm cable than two 2.5mm cables. Also, you can't guarantee just how the current with split down two cables.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

are supposed to be accessible. The full-on answer would depend on the function the switches are considered to be performing: if emergency shutoff, then visible-and-accessible; if isolation, less accessible would be permitted. Let's use common sense here: definitely one of the reasons you want the switches is to cut power to your cooking appliance if something catches fire on it or in it. Then you want to be able to cut the power PDQ alongside doing Other Sensible Things (covering with well-dampened towel, for example) - and the "you" might just be Auntie Mabel cooking lunch for all of you. Hence the requirement for the switch to be in plain view and close by - i.e. I'd think long and hard about pretending a cooking appliance isolator does *not* have any emergency switching function.

That's the general idea - the load is shared among the two paths to any place on the ring. But it's not shared half-and-half other than at the midpoint of the ring - it's in proportion to the resistance of each path, which is mainly determined by the length of each cable path back to the CU, along with how well each joint along the way has been made. That's why you can't just double the current-carrying capacity of the 2.5mmsq cable in designing the ring: and also why it's poor practice to design a ring layout in which heavy loads are concentrated at one end of the ring - e.g. a ring to serve all downstairs which starts off in the kitchen, where the heavy loads are, and then snakes lazilly all round the house before coming back to the CU.

for split-level hob-n-oven setups and similar separate-cooking-appliances setups: by and large the conventional circuit design assumes there'll be one hulking great standalone cooker. Such cookers have a *peak* current draw of say 40A (turn on 4 rings - there's 7kW - and both top and bottom ovens - another 3kW - look, ma, 10kW peak loading giving a current of 10,000/240 = 41.3A; or if you prefer to work with the nominal-voltage fiction, 10,000/230 = 43.5A, though if the supply voltage did drop to 230 the power drawn through the cooker elements would also fall). Now, that peak load won't be sustained for long, even if Auntie Mabel is cooking Christmas dinner with all the trimmings and using all 4 rings and both ovens, because the simmerstats/thermostats will be switching each bit of the cooker on and off. That - and the fact we don't in practice turn on all our cooker's component loads at once - is the thinking behind the diversity rule which allows us to treat the worst-case-40A-plus load of the cooker as less than that (10A + 30% of the rest in a domestic setting) for purposes of counting up the total demand of the installation. *But* we still size the wiring and switchgear for this appliance which on occasion *will* draw its full 40A to suit that peak demand. (And voltage drop along the length of the cable matters too). Hence, the Right Answer is almost always 6mmsq for the dedicated cooker circuit feeding either a single cooker, or split later to feed oven + rings as separate appliances.
So, 2.5mmsq rings do not 'take just as much loading as a 6mmsq radial' - the dedicated circuit is much more appropriate to supply a single load, and can safely meet a higher sustained load than a 2.5mmsq ring.
HTH - Stefek
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Just a quick follow-up on the form of the control switch used for each feed off the radial. Are there any regs about this concerning what the switch implies about the underlying electrics? In other words, is it against the regs to use (if you were stupid) a cooker-type switch when the supply to that is actually off a standard ring circuit? If the switch also had a three-pin plug outlet then someone might assume they are safe to power their hefty cooker or hairdryer off that. My reason for asking is to determine whether the control switches for both feeds off my cooker radial can/should be cooker-type switches, to indicate that both are fed from a cooker radial, or would this imply that both have dedicated radials behind them? Or does it not matter? I guess any electrician would be able to tell with a little detective work, but I'm thinking more of Aunt Mable here. Forgive my use of inappropriate terminology.
Thanks.
Michael Brewer
snipped-for-privacy@hp.com wrote in message wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Michael Brewer" wrote | Just a quick follow-up on the form of the control switch used for | each feed off the radial. Are there any regs about this concerning | what the switch implies about the underlying electrics? In other | words, is it against the regs to use (if you were stupid) a cooker- | type switch when the supply to that is actually off a standard | ring circuit?
That would be a switched unfused spur and could only be used for supplying one FCU or one single or twin 13A socket, which would be within the regulations. (And a twin 13A socket is not assumed to take 26A. The ring final circuit is designed for general domestic use for a variety of equipment where diversity will apply. It is the designer of the installation's responsibility to not use a ring final circuit where it is inappropriate, eg fixed heavy loads.)
If you're talking about using a cooker control unit to supply a cooker, but off the ring final circuit, then of course it's against regs.
| If the switch also had a three-pin plug outlet then someone might | assume they are safe to power their hefty cooker or hairdryer off that.
But that would be limited to 13A by the plug fuse.
| My reason for asking is to determine whether the control switches for | both feeds off my cooker radial can/should be cooker-type switches, to | indicate that both are fed from a cooker radial, or would this imply | that both have dedicated radials behind them? Or does it not matter?
Provided that the circuits are clearly labelled at the CU it should be obvious that the two outlets share a circuit. The switches should be clearly labelled so it's obvious (especially to Aunt Mabel) which controls what. Some switches come with a set of stickers (cooker, hob, oven, water heater, etc) rather than just being engraved cooker.
Owain
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I have a feeling I'm breaking all sorts of rules by following up my own original posting, but it seemed to apply to the whole thread.
I have noticed a footnote in the oven specs (it's a Bosch oven) that says "we recommend that all models should be connected using a fused spur outlet". This footnote applies to all the ovens, including the double ovens.
According to my very limited understanding, a "spur outlet" would imply to me that it's a spur off a ring circuit. Or could you have a spur off a radial circuit, e.g. a multi-point radial circuit where you provide a number of fused outlets tapped off the radial circuit?
How would you interpret this footnote?
Many thanks.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It seems to imply that it wants a 13A FCU. However, it could be translated European stuff. They traditionally run each appliance off a dedicated 16A circuit, a bit like old UK 15A round pin circuits.
Do the instructions state a value for the fuse?
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.