Normally a ring circuit would start at the CU, and then at the CU.
Is it allowed to have a length of 6mm cable from the CU, then from the end of this, run a ring, terminating again, at this end of the 6mm cable?
If not, why not!
Sparks...
What I meant to say was...
Normally a ring circuit would start at the CU, and then END at the CU.
Is it allowed to have a length of 6mm cable from the CU, then from the end of this, run a ring, terminating again, at this end of the 6mm cable?
If not, why not!
It's not that I need, or want to do it, I am just curious!
Sparks...
It's not forbidden: both sections would be appropriately rated for a 32A MCB, subject to maximum length being calculated.
BUT (a) it would definitely need Calculation, as it's not one of the Conventional Final Circuits pretabulated in the OSG; (b) being outside the Conventional Final Circuits designs, it's going to confuse any 'normal' person (jobbing electrician or d-i-y'er) who sees a single
6mmsq cable going out of a CU way labelled ' ring', and (c) you'd have to provide access at the transition point between the 6mmsq feeder and the two legs of the ring, to allow the testing for ring continuity which is (in theory ;-) done during a periodic inspection - which requires access to the two ends of t'ring and which yer sparky expects to find at the CU.Unless someone else can point to chapter-n-verse in Regs or OSG which specifically rules out this derangement?
Stefek
Unusual in domestic, but quite commom in industry, BUT in industry the 6mm would terminate in a RCD/MCU which would then feed the ring, ie the 6mm becomes a sub main. In fact just done this very thing in our factory to feed several assembly benchs.
Dave
I would suggest that it's more common than you think in domestic use, what about houses with un-attached garages / workshops, they often are supplied via a sub main to a RCD/MCU etc. ?
Like my shed does I guess!
I need to start a new thread about this...
I'd agree - but that's no guarantee of it being a good idea - there are allsorts of well-dodgy practices that are actually "quite common"
That's a sub-main - different thing, well accepted. It's different because the ring splits immediately after the protection device.
I've certainly seen rings fed from a single cable, mainly for rings on upstairs floors of 3 & 4 storey houses. I've also seen this single feed done with 2.5mm and showing signs of overheating (HOMO with electric fan heaters in the upstairs flats). Shiny new test certificate from a NICEIC sparky too.
Read the OP again, no suggestion of a RCD/MCB at the end of the 6mm.
Dave
I was replying to your comments, "....BUT in industry the 6mm would terminate in a RCD/MCU which would then feed the ring...." !
I was replying to your comments, "....BUT in industry the 6mm would
terminate in a RCD/MCU which would then feed the ring...." !
It would need to terminate in some from of device as the capability of
2.5 ring circuit is 2x 26.5 A where as the 6mm is rated a t 42A method or less if run in any other way. Albeit that it might be supplied with 32 A breaker, but might just as easily have a 45 A breaker stuck on i instead, usual trick when people decide to replace 7.5 or 8.0 kW shower with the 9 - 10kw devices available now, often with integral pump a well!. Have seen more than one or two 6mm cables showing heat distress 10mm cable would be ok, but if doing this it would be simpler to wire i as a radial circuit with 4mm t&e to each socket. It would also be futur proof in the expectation by 2007 of the adoption of the 16A euro socket and plugs we are going to be gifted with-- Miketew
Yes, because in normal domestic situations excluding shed supplies etc sub mains are rarely used, the ring begins and ends at the cu as you know. Any way we can argue dotting the i until the cows come home.
Cheers
Dave
It's not quite April 1st, surely you jest sir ?
The capability of a standard 2.5mm ring final circuit is 32A with an expected max design loading of 20A at any point. Where do you get '2 x
26.5A' from?
Anyone who replaces a 32A with a 45A MCB -- especially on a circuit labelled as 32A ring -- should take responsibility for their incompetence. It is very unlikely that a properly designed 32A ring would become inadequate and require uprating to 45A on load grounds -- the main problem is their use in kitchens causing an imbalanced or point load.
It would not be future proof, because a 4mm 32A radial would be subject to the same possibility of upping the MCB to 45A you took umbrage at two paragraphs above. Also a 32A radial would not be suitable for unfused euro sockets/which must be supplied on 16A circuits as that is the rating of the appliance flexes.
Owain
It would be more like Christmas ! But alas the demise of the digusting 13A fused plug is currently being twarted at every turn by the morons at the IEE. 2017 would be more realistic.
Would this mean all cables from the 16A euro plugs would have to be rated at
16A to achieve the same safety as the current system (Where if the plug has a 5A fuse, the cable can be also rated accordingly)?Or do the euro ones have a fuse I don't know about! Or would they just be less safe than the current ones?
Sparks...
No, only short-circuit protection of the flexible cord has to be considered, not overload. For normal lengths of flex the 16A fuse or MCB will protect a 0.75mm^2 flexible cord.
It's a similar argument to the one that says it's not really necessary to fit a fuse smaller than 13A in 13A plug - a 13A fuse will protect a
0.5mm^2 flex perfectly well.But 0.5mm^2 flexibles are hardly used nowadays, so a change to a harmonised plug-and-socket system (which will probably never happen) will not lead to any increase in flex sizes.
So they are not as safe as the ones we have now that will portect against overload? You say the 16A fuse or MCB - Does this mean every single sockect it protected by a seperate 16A fuse/MCB not a 32A or 20A fuse/MCB as is now?
Against a short, but would it protect against an overload condition?
Next they will be trying to get us to drive on the other side of the road! Love to see them phase that one in!!
Sparks...
There is to be a Euro standard which will preclude a ring circuit in the future. Rings are only common in the UK and Ireland.
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Well..... one doesn't hear of significant numbers of accidents/fires in countries using Schuko connectors as long as they have good wiring workmanship as well - e.g. Germany, Nordic countries etc.
The obvious solution would be to do it in stages. Trucks and buses one week and cars the next.
Fiar enough, just dont mention Spanish wiring!
I guess, Leaving the bikes till last I guess!
Sparks...
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