Not sure I'd go for that actually: Two 13A appliances on either one would pop the mcb. Not that I have many things that draw that much, but it would be good to know things weren't quite so close to the limit. For example, using a 3kW heater in the garage then turning on a power tool that draws a bit on startup might pop a 20A circuit but not a 32A. Not the end of the world, but a bit of a pain all the same. (and possibly a bit unlikely as I try not to use power saws, routers etc inside as it makes such a king mess without a decent vacuum setup)
To be fair, a 20A MCB will carry 26A of load pretty much indefinitely. While it would probably be more than adequate for a garage, it might be a bit restrictive for a utility room (depending on size and likely appliances).
Possibly - although remember it takes 100A of inrush to open a type B
20A MCB. The usual culprit for tripping a 20A I find are things like big
110V site transformers.
One could upgrade the MCB at the origin to 40 or 45A, then have 32A ring in the utility room, and a 16 or 20A radial in the garage (the latter if using tools there). Lighting for the garage could either run from a separate circuit or from a FCU on the power circuit. Again depends a bit on likely applications.
The likely applications does matter but a utility room would typically have only a washing machine and a tumble trier. So 26 A max (less with most machines as they are not 3kW) for short time periods even when they are turned on at the same time. Now if the garage was a workshop that would be a different matter.
In the real world the UK's 32A ring final circuit reigns supreme and is all the OP needs to supply the two rooms. Lesser countries can stick to their radial circuits.
Over 90% of the houses I work in have just one ring supplying the downstairs or just the kitchen and they do not have an overload problem even when supplying typical household loads such as washers/driers/microwaves/toasters/kettles.
Yup agreed. Add a dishwasher in there and you might be borderline...
Depends on what you work on! (a 32A circuit seems to cope with any load I can throw at mine - but then again that is setup mainly for woodworking not welding or home forging!)
Indeed - my kitchen / utility room ring probably has getting on for 15kW of potential load on it. Never a problem in practice.
Of course, that's the bottom line isn't it? My last place had a single
32A ring for the kitchen, utility room, garage sockets and a whole bunch of other stuff and never had a problem. (Mind you, old re-wireable fuse, not these new-fangled mcbs that pop everytime a light bulb goes....)
Having moved, we still have the same (usual) range of appliances and that goes into the new room will be a proportion of what currently runs on the 32A kitchen ring, so I can't see any major problem in terms of the overall load.
The garage component will, realistically, take very little (as much as I'd like a workshop!), just things like cordless drill chargers etc, so I can't see that putting too much strain on things. Obviously it needs a beer fridge there, as I don't have a shed.....
Mr Rumm's 2-circuit suggestion is interesting but I'm not sure I really need to provide that much juice overall at present. It would provide future-proofing however.
I guess that's where I started though: My first instinct was to go with convention and put in a ring, as a 32A ring seems to stand up well to normal 'real world' use.
It just 'feels' a bit odd to add a ring to the existing single 6mm cable (does that make it a lasso, or a noose, rather than a ring?), except through a mini CU, whcih itself seems superfluous if the circuit is already protected adequately.
Since the sockets will run physically in a row, a radial would be an easy design, especially if it's OK in 4mm, as it means there's no need to run the return leg of the ring. Of course, I hadn't realised it could be unpatriotic to use a radial, so I might have to reconsider...
At least both spaces already have lights .....Maybe I should just do what my Dad would have done and tap into the lights with a bit of bell wire, twisted on under a wrap of tape, to run the washing machine....
The reality is that you could quite legitimately stick a normal 2.5mm^2 ring on the end of your radial (with a nice big junction box), and take a feed off that via a FCU for the garage lights. Total cost in extra hardware, under a tenner.
The only thing the CU buys you is the ability to drop cable sizes after the main feed, and also later upgrade the MCB at the origin should you want to, without worrying about downstream effects. (also a bit better form isolation and discrimination etc)
Yup you could do that. Arguably there is normally a requirement to fuse at the reduction in cable size, however in this case, your upstream MCB is already sized to protect the 4mm^2 anyway (unless you de-rate it in some way by the choice of installation method)
If you go this route, just do a quick calculation on the earth loop impedance to make sure its still in spec, since you won't find that circuit in the OSG with a specified maximum cable length.
On Thursday, January 24, 2013 7:38:00 PM UTC, snipped-for-privacy@blueyonder.co.uk wr= ote:
I was not entirely happy (though I haven't yet accumulated enough tuits to = get anything done) to discover that my entire house (3 floors plus cellar, = with a fused spur to the garage) runs on just *one* ring, and the second 30= amp fuse in the CU just supplies the cooker (not used since I have gas) pl= us the single 13A socket in the combined cooker outlet. That said, I've nev= er had any overload problems with it - so far... I believe this had been done by the previous occupant, whose day job was as= - an electrician. There were other annoyances, too - the hall lights were = not two way switched, and the switch for them was about 4m from the front d= oor, so if you forgot to leave the light on in the morning you could end up= feeling your way along the hall in the dark...
It's also patriotic to use a 32A radial circuit:-)
That's what I fitted in my brothers garage (ie a working garage not one for car parking). I was far too lazy to use the ladders twice and install a ring:-)
And last year I fitted a 4mm 32A radial in a kitchen as it was just like your set up. A CU and a line of sockets. It's rare that I do that install but it was perfect for the job
It's the 20A radials I do not like as they often are too limited when supplying more than one socket.
Guess who was in school again this week when a 20A radial tripped because of the electric heater they plugged in?
I have an American military surplus 3KW 240/120 V. autotransformer which regularly tripped a 32A. ring MCB, until I put a 10 microfarad capacitor across it. On the face of it, that might *increase* the inital inrush current (although it's very roughly right as a power factor correction), but somehow it doesn't. Maybe it just reduces residual core magnetisation after switch-off, when you'd expect an exponentially-decaying oscillation, and that in turn reduces the later inrush current when the thing is turned on again.
I doubt if many site transformers contain a capacitor.
Phew - at least I won't get deported if I put one in then ;-)
Sounds a bit limited to me too. Making this into 2 x 20A radials might mean constantly worrying about what's drawing current to stop trips, whereas a single 32A (radial or ring) should behave like any other circuit. If I ever think about putting any hefty things in the garage to make it a workshop, I can think about the power at that stage.
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