MCB Current Rating for Ring Main

Is there anything that says an MCB rating for a ring main has to be 32 amps, could it be 16 amps? I want to put my kitchen on its own circuit but the MCB's are no longer made by Crabtree but I have two unused 16 amp MCB's. If I use the 32 amp that is currently the downstairs ring main for the kitchen then put the front room/hall on one 16 amp ring and the living room on another 16 amp ring would I run into problems?
Kevin
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Kev wrote:

Probably not, obvoiusly the max current available for each circuit would be lower. You wouldn't have to use rings, 2.5mm on 16A would be accepyable for a radial circuit.
What you must not do is attach one end of the ring to one MCB and the other end of the same ring to the other MCB...
Owain
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You might get some nuisance tripping if you try doing the hoovering and ironing whilst watching a DVD with surround sound by the light of a collection of floor lamps :-)
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Are you are refering to the Crabtree MCBs that came before the plug in type? ie is it a screw the fastens the MCB to the bus bar? If so then I was able to buy a 40 amp one from Newey and Eyres last week. I did have to order it in but it did arrive the next day. I am also sure I will have an old type 32 amp MCB knocking about in the garage, it will be guaranteed second hand but I will post it to you if you want.
Adam
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ARWadsworth wrote:

It is a plugin type. The current starbreakers have exactly the same type if fitting and are interchangeable but the newer ones stick out more and are supposed to foul the front cover slightly. I may just try one and see. The cover has a lip that I could file down a bit if the fit interfears.
Kevin
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I also have those types of MCBs knocking about if you want one.
Adam
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Kev wrote:

it can be 16 if you want. 16A mcbs dont trip at 16.1A, and as long as you dont have kitchen, immersion or electric heating on them, all should be fine.
NT
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Hi;
Good idea to have a seperate final ring circuit in the kitchen. Most sparks I know who do this would use 4m T&E as well.
If you have the kettle on, switch the toaster on while the kettle boils then warn the beans up in a Micro wave, what happens ?
Didn't trip, Umm, now the fridge kicks in and it does trip!!
Is it worth the cost of a 32 Amp MCB ?
Who is going to Insect and Test this for your Part P certificate? I would probably fail it on the grounds of the MCB being too small to take a kitchen load by exposing the MCB to too much in overcurrent operations. What if the MCB failed in the ON position, Presto - No protection and you would not know - hence the need for Part P.
Then, perhaps the Kettle is on the cooker switch and all is fine.
Regards Ian
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snipped-for-privacy@pipemedia.co.uk wrote:

Serves you right for putting the fridge on the socket circuit, then. Fridges better on their own non-RCD circuit (except TT installs, obvoiusly). But that's usually too much work for a "pro" sparks.
Anyway, kettle = 2kW, toaster = 2kW, m/wave = 1kw
total = 7kW, within loading of 32A ring.
If kettle 3kW then a short term overload, which should be well within the parameters of the ring if the cable and MCB are correctly sized together.

What?
Exactly how does Part P make any difference to the IEE wiring regs and the BS for circuit breakers?

If you think having kettles on cooker switches is fine I'm not letting you near my house.
Owain
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Owain wrote:

In my case the fridge and the freezer are on their own unprotected circuit anyway so that wouldn't be a problem.
Kevin
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snipped-for-privacy@pipemedia.co.uk wrote:

I will put the existing 32 amp on the kitchen. That would leave two unused 16 amp MCB's, one for the front room/hall and one for the living room. If I could get an old type plugin 32 amp I would but tracking one down is the problem.
Kevin
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snipped-for-privacy@pipemedia.co.uk wrote:

You say 'I would probably fail it' - are you a tester of some variety?
NT
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Kev wrote:

16th ed IEE wiring regs is very lean on requirements for ring circuits. Most of the stuff in earlier editions has been taken out and appears (if it does) in the IEE On-Site Guide - mostly in Appendix 8. There's some relevant additional info in Appendix 1 (diversity).
Appendix 8 implies that ring final circuits should be protected at 30A or 32A & be run using cable rated >= 20A - ie >=2.5mmsq if in FTE.
Possibly there is a further implication in Appendix 8, that if you use BS1363 socket outlets (the std uk flat pin type) then any ring they are inserted in must comply table 8A - ie for a ring circuit you need 30/32A MCB.

Frankly a false economy. Use some of the money you are saving by DIY to do a proper job with fittings that will last. Invest in a new CU if you possibly can.
HTH
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jim_in_sussex wrote:

Although there's nothing wrong with the OP's idea of using the one available 32 A MCB for the kitchen ring and splitting the other ring into two radial circuits, assuming each circuit covers <50 m^2 floor area. However, these should be 20 A circuits, not 16 A. With 16 A MCBs they would be non-standard circuits and could be seen as under-rated for general household loading - likely to be overloaded if the CH breaks down and all those old electric heaters come out, for example.
--
Andy

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Andy Wade wrote:

...but unless I have very much misunderstood the original post, the suggestion was to break the circuit into 2 separate 16A rings.
As you suggest breaking it into 2 radials is perfectly OK (or even just making it into 1 20A radial) & might make the OP's MCB hunt easier as finding a 20A MCB would also put him back in business.
How does the risk of reusing old MCBs untested rate versus installing a brand new reputable make CU with only basic continuity testing ? My money would go on a the new CU as the safer bet.
If the OP is reusing old second hand MCBs then perhaps he should consider testing them properly.
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How do you test an MCB?
Adam
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ARWadsworth wrote:

With a big bank of lightbulbs, a stopwatch, and the time/current curves?
Owain
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ARWadsworth wrote:

Pass current through it and see if it trips. Use a variac and a low-voltage high current transformer, and wind the current up slowly. Not really necessary though, since (IME) they never fail, unlike RCDs.
--
Andy

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That is not a test used on any NICEIC inspection. Maybe it should be.
Adam
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On 8 Jun,

I remember testing in that manner, (after it had twice failed to trip, resulting in the 100A incoming fuse (and its replacement) blowing.) a 6A MCB. Everything was in spec, It just wasn't up to the (particularly high) PFC present on that circuit. I've been a little wary of MCBs since.
--
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