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Discuss Newbie question... garage circuit connected to ring final circuit. in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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Hi,

I am studying for me 91 and am currently practicing on my home. I have found that my garage circuit consisting of a small 2 way CU with 1 of each; ring and lighting circuit (no RCD). I expected to see this circuit connected to the main CU through its own CB but in fact it is connected to one of the ring final circuits (via a double socket as a spur) and the spare 32A MCB in the main CU not used. I believe, but doubt myself, that this is a C2 because of circuit interconnection and that only an FCU (max 13A) could supply more than one spur (but not the lighting circuit).

Is my logic correct, and if not why not? If I am correct would this constitute a C1 rather than a C2? The rest of the circuits are fine. I scratch my head as to why somebody would do this when there is a spare way in the CU and both the dist board in the garage and the CU appear to be just a few years old.

Any guidance would be greatly appreciated. If I am wrong please can you give me an explanation?

Thank you.

FYI I only have Amendment 2011 knowledge.
 
  • Thread Starter Thread Starter
  • #3
Hi,

I have the same guide, but what is the definition of a cross-connected circuit? As it is not connected to the same CU but is connected like a spur is it really cross connected?
 

Jimmy Boy

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Arms
I would be grateful if you would tell us before engaging in any further dialogue, what qualifications you currently hold, what books you own to refer to to obtain this '91 you refer to ? If my response seems arsey I don't apologise, but the tone of your question makes my alarm ring a bit.
J
 
Well it certainly doesn't meet the definition of 'standard circuits'. However, if you were to put a fused spur before the garage CU, then it just about comply. although using a final circuit to supply distribution equipment is bad practise.
 

rich.250

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Arms
So a spur off the RFC exceeding 3metres?? Needs fusing down then.
IMO I don't like this arrangement at all!! And if it was my house I'd just put a sub in and have done with it :)
 
Also all connected equipment of a RFC should comply with bs1363...
are you sure this is the case? I don't think FCU's are to BS1363?
 
O

Octopus

So a spur off the RFC exceeding 3metres?? Needs fusing down then.
IMO I don't like this arrangement at all!! And if it was my house I'd just put a sub in and have done with it :)
Seen it lots of time, done it a few times, but always using a 13A FCU as the connection point. Sometimes its the only way!
 

rich.250

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Arms
Yeh I don't have a problem really from a swfs. Only other thing is segregation of Rcd's and fuse/breakers....
But that's only if it feeds a db out there.
 

rich.250

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Arms
are you sure this is the case? I don't think FCU's are to BS1363?
Bs 1363 part 4 1995 I believe :)
 
Bs 1363 part 4 1995 I believe :)
Ahh. ok I stand corrected, I thought BS1363 was only the plugs and sockets!

In that case All equipment connected to an RFC should be to BS1363 :smile5:
 
Though not a great lover of the OSG there are some good guides in it and one is the 1/8 one (Page 68 Section 7.2.3) , that an unfused spur length off of a ring should not exceed 1/8 of the furthest point of the ring.

The 3 metre ruling would not apply to a RFC simply because

1) Your concerning yourself with the overload side of things, or you should be. The earth fault protection should still be provided by your 32amp protection device provided that the spur would not exceed that Zs value for that device. Which is why the 1/8 rule is pretty good, if you ensure this there is very little chance your spur will fail on Zs

So it is more the over load side your concerned with, that is a single 2.5mm cable being protected by a 32amp PD. Well that is where I agree with you concerning a spur should only connect into a BS 1363 accessory, because these accessories all are limited to 13amps and you therefore conform to reg 433.2.2

This is why I always say to guys who ask can I spur of a ring final into an enclosure and just put 6amp for lighting and a 10amp for socket no. IMO it is a bad design and opening the design up to abuse

Yes in theory you can, that 16amp load will not stress a 2.5mm cable. But even in a domestic situation there could be a chance that you may have a problem with a socket(s), you may have a fridge/freezer on it and a washing machine and it may just trip occasionally when the heating element is on and the fridge starts up, so what happens ,the MCB is increased to perhaps a 16amp or even more.

By designing a spur into a non BS 1363 accessory is opening up that circuit to abuse in the future and IMO bad practice.
 

rich.250

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Arms
I do agree Malcolm, totally.
far to many circuits are badly designed now, and do not comply on many levels.
Im sure I was told 3metres max length for a spur on my 2391 course. Maybe a over the top limit.....
Tbh I never really checked.
Personally I would never really have a spur exceeding 3m as i dont see the need.
knowing what people are like... from the one spur they will have two 13amp appliances LOL

I too am not a fan of the OSG maybe why I missed the 1/8 th rule. Will have a look.

Thanks for the reply :)
 
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