Lighting circuit taken off ring main somewhere

[Ross1]

evening guys, ive come across lighting in one room of domestic premises that has been supplied from the ring main at some point. the cable coming from the ring is 1,5mm which goes through the switch then on to the 2 x 12V down lights. This is on an EICR I`m doing. There is no chance at all of accessing under the floor boards as there is very expensive oak flooring down every where. I believe that from memory you can use a switched fused spur for functional switching. I could then put in a 5A fuse and the load side of the cable will be protected. My concern though is the piece of 1,5mm from ring to switch? your thoughts on this would be welcome. I see this as no different to taking a spur off the ring for an extra socket etc, or am I forgetting some thing?

 

[LittleHelper]

I take the same view as 7029 Dave when approaching similar situations as a good practice measure.

 

[GLENNSPARK]

to the O/P:

the cable feeding the FCU is adequate & compliant (CSA)..
do the usual (IR, loop)..to verify....

 

[AndyL]

Because its not the way we usually do it does not make it bad practice.
As stated above the FCU protects the 1.5 against overload. The MCB will still give adequate fault protection (Zs being correct of course!)

 

[michaelk]

Could you not fit a fcu with 5a fuse in it next to the socket the 1.5mm is coming from and put the 1.5mm on the load side and a bit of 2.5mm between the socket and fcu next to it.

 

[telectrix]

Could you not fit a fcu with 5a fuse in it next to the socket the 1.5mm is coming from and put the 1.5mm on the load side and a bit of 2.5mm between the socket and fcu next to it.

because it's probably joined into an inaccessible Jb under the oak floor. i'd just bung in an unswitched FCU with a 3A (or 5A) fuse before the light switch.

 

[Badged01]

Try Reg 433.2 to cover you for ommission of overload protection on a conductor ....

 

[Pete999]

Replace the 1.5 feeding the switch (replace switch with FCU) with 2.5 simples it aint rocket science it's in the OSG plain as the nose on your face, no arguments just do it right the first time as Mike Holmes says.

 

[D Skelton]

Put it this way, if I carried out a job whereby I fed a FCU with 1.5mm from a ring final and some muppet came arond telling the customer it's bad practice and against regulation blah blah blah... That is SLANDER! Plain and simple! If you then proceeded to charge the customer to replace it that is obtaining money by deception, a criminal offence!

Any of you idiots out there that continue to propagate this myth that somehow the 1.5mm cable isn't protected are talking out of your rear end. I would suggest that you start by picking up a bloody regs book!!!

 

[spark 68]

Replace the 1.5 feeding the switch (replace switch with FCU) with 2.5 simples it aint rocket science it's in the OSG plain as the nose on your face, no arguments just do it right the first time as Mike Holmes says.

Why?

Yes look at the guide for a guide (sarcasm), while at the same time ignoring the forward fusing rules (section 434) in the BGB.

Even the picture in App 15 tells us it does not cover other aspects of the design.

 

[ged noden]

If you can find which socket the 1.5 cable is fed from, then you can mount a spur unit next to it.
Quite simple.

 

[kingeri]

If I was installing this from scratch I would fuse down at the point of CCC reduction. If it was already present and as described by the OP, I would leave it as it is, there is absolutely nothing wrong with it.

 

[Badged01]

I would suggest that you start by picking up a bloody regs book!!!

OK, to continue the discussion I'll try ....... as I understand the regs the C/B is installed to protect the cable, which in this case I read it as a 32A C/B protecting the 1.5mm cable fed off 2.5mm cable. So the 1.5mm cable isn’t being overload protected by the 32A C/B.

But regs do allow that if due to the cable load characteristics it isn’t likely to be overloaded then overload protection isn’t needed --- provided there is fault protection. For the 12V lights connected via a transformer I’ll take this as holding true for overload and the 1.5mm cable is good to use without circuit overload protection.

However, Ive still got to provide fault protection for this 1.5mm cable even though I don’t need overload protection. I’ll assume an RCD so a L/E fault is taken care of but what about a L/N fault? Will the cable hold out before the 32A C/B or DNO cut-out “pops”?. Using the let thro current calc will probably show the 1.5mm cable can handle this energy and is OK to use.

But if it cant handle the fault, how do I now provide fault protection for the 1.5mm cable?

 

[spark 68]

The FCU need not be before or at the csa reduction point, it can be within 3m of it downstream.

 

[AndyL]

OK, to continue the discussion I'll try ....... as I understand the regs the C/B is installed to protect the cable, which in this case I read it as a 32A C/B protecting the 1.5mm cable fed off 2.5mm cable. So the 1.5mm cable isn’t being overload protected by the 32A C/B.

But regs do allow that if due to the cable load characteristics it isn’t likely to be overloaded then overload protection isn’t needed --- provided there is fault protection. For the 12V lights connected via a transformer I’ll take this as holding true for overload and the 1.5mm cable is good to use without circuit overload protection.

However, Ive still got to provide fault protection for this 1.5mm cable even though I don’t need overload protection. I’ll assume an RCD so a L/E fault is taken care of but what about a L/N fault? Will the cable hold out before the 32A C/B or DNO cut-out “pops”?. Using the let thro current calc will probably show the 1.5mm cable can handle this energy and is OK to use.

But if it cant handle the fault, how do I now provide fault protection for the 1.5mm cable?

Going round in circles here, see my earlier post. Fault protection will be supplied via the CB.

 

[Badged01]

Fault protection will be supplied via the CB.

True, if the 32A C/B can do the trick for 1.5mm cable?!?!. But the question was aimed that if the 32A C/B cant (and there isnt an FCU fitted for overload protection) how is fault protection now covered?