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?

 

[7029 dave]

yes nothing wrong with spurring down lighting circuit of ring main. ( bad circuit design). But that 1.5mm cable needs to be replaced to 2.5mm to feed side of spur

 

[GLENNSPARK]

yes nothing wrong with spurring down lighting circuit of ring main. ( bad circuit design). But that 1.5mm cable needs to be replaced to 2.5mm to feed side of spur

does it?

are you sure

 

[Ross1]

I agree with what you are saying Dave, its for sure bad practice but from a technical point of view that 1,5mm supply to fused spur is inaccessible so no chance of to many amps being pulled through it.

 

[Newbyspark]

Wouldn't the fuse blow if more than 5 amps was being drawn, then the 1.5 cable before the fuse wouldn't be drawing any amps either.

 

[7029 dave]

understand but that cable is underrated for that circuit.

 

[Ross1]

understand but that cable is underrated for that circuit.

what about when you spur of the ring to an additional point as allowed. that 2.5mm is also under rated for the 32A MCB.

 

[GLENNSPARK]

understand but that cable is underrated for that circuit.

David...
whats the minimum CSA for FCU feeds?
and given that the largest fuse to BS1362 (13A) is under the max CCC of a 1.5/1.0 flat twin....
the fuse will dictate Max demand here so...

 

[7029 dave]

what about when you spur of the ring to an additional point as allowed. that 2.5mm is also under rated for the 32A MCB.

Take your point but its being feed by 2cable's ie lets say half the load between 2 cables.

 

[GLENNSPARK]

Take your point but its being feed by 2cable's ie lets say half the load between 2 cables.

eh?
dont get your drift here David...

 

[7029 dave]

David...
whats the minimum CSA for FCU feeds?
and given that the largest fuse to BS1362 (13A) is under the max CCC of a 1.5/1.0 flat twin....
the fuse will dictate Max demand here so...

Yes Glen I take your point that FCU aint gonnar pull more than 13amp tops (max) or min 1amp depending what size fuse you put in so yes it will dictate max demand.But its just bad practice to have that size cable.

 

[D Skelton]

But its just bad practice to have that size cable.

By that rule then every tail I take from a 200A busbar chamber would have to be 95mm??? Have you tried fitting 95mm cable into a 100A switch fuse?

It's not bad practice at all.

 

[GLENNSPARK]

By that rule then every tail I take from a 200A busbar chamber would have to be 95mm??? Have you tried fitting 95mm cable into a 100A switch fuse?

It's not bad practice at all.

about time.
Evening Damian...

 

[GLENNSPARK]

Yes Glen I take your point that FCU aint gonnar pull more than 13amp tops (max) or min 1amp depending what size fuse you put in so yes it will dictate max demand.But its just bad practice to have that size cable.

David...
you need to rethink statements like this ...as they are misleading to the pups in here...

 

[D Skelton]

Evening Damian...

It is Glenn, it is

Goooooood Evening!

 

[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?

 

[AndyL]

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?

I understood from OP that there is FCU fitted, this give overload protection.

From reg 434.5.2 the 1.5mm cable will reach its limiting temp in about 1.6 seconds (assuming 160A fault current) As the CB will operate in about 0.1 seconds, at this current, fault protection is afforded

 

[Badged01]

I understood from OP that there is FCU fitted, this give overload protection.

Sorry if my reply has confused but the thread is directed along there being no FCU fitted for protection, hence my question for how to protect for fault current in the unlikely event that the 32A C/B cant!.

 

[AndyL]

If there is no FCU then overload protection would indeed be required, fault protection is still given by 32A CB

 

[Zeus]

you are right that you can take lighting off a ring final circuit and I know its bad practice to use 1.5mm cable to do the first leg of that circuit extension with but as 1.5mm can carry up to 16A, that first leg will only be carrying the load of the lighting to which you will have a 5A fuse in series. so I would make sure firstly that the 1.5mm does not form part of the ring final circuit and if this proves so then I would have said it is ok to remain. just note as a code 3 on your report.

 

[Guest55]

youre all missing the point !
the OP declared this to be an eicr , therefore the only discussion should about the coding if any.
and IMO its probably a C2 - but a 2 minute fix with a switched fused spur.

 

[Badged01]

youre all missing the point !

You're being far too serious and stopping us having all this fun and banter to liven up the day

 

[Guest55]

im never serious !
seriously.
;-)

 

[GLENNSPARK]

but even after prominant members in here made it quite clear that it was acceptable to use a 1.5 as a feeder to an FCU there were still several others continuing blubbing on about how they would rip out the 1.5 and replace with 2.5....
an unneccessary nonsense if you ask me
christ, what do some in here think we fuse down for?

 

[shanky887614]

but even after prominant members in here made it quite clear that it was acceptable to use a 1.5 as a feeder to an FCU there were still several others continuing blubbing on about how they would rip out the 1.5 and replace with 2.5....
an unneccessary nonsense if you ask me
christ, what do some n here think we fuse down for?

The fun of it?

Lecky takes easiest route so splicing cable then adding fcu would be more than adequate.

If i was installing myself though id probably use 2.5 to fcu but woudlnt replace if it was done in 1.5

 

[telectrix]

but even after prominant members in here made it quite clear that it was acceptable to use a 1.5 as a feeder to an FCU there were still several others continuing blubbing on about how they would rip out the 1.5 and replace with 2.5....
an unneccessary nonsense if you ask me
christ, what do some n here think we fuse down for?

prominent, glenn. get a grip, man. :angelsad2:

 

[GMES]

What really scares me with threads like this is how many so called electricians seem to think it is dangerous to utilise the 1.5mm to a fused spur, as stated by Glenn spark and others it is perfectly ok to do this, I sometimes wonder where the train of thought comes from to rip someone's house apart just because they don't seem to understand the basics of electrical work.

 

[GLENNSPARK]

What really scares me with threads like this is how many so called electricians seem to think it is dangerous to utilise the 1.5mm to a fused spur, as stated by Glenn spark and others it is perfectly ok to do this, I sometimes wonder where the train of thought comes from to rip someone's house apart just because they don't seem to understand the basics of electrical work.

its a waste of time as well when after stating such facts there are still those that refuse to listen..
and so will go forth and ruin decor/cost unneccessary cash/invent non-existant remedial works....all a con..as Damian quite rightly pointed out earlier in this nonsense...

 

[GMES]

its a waste of time as well when after stating such facts there are still those that refuse to listen..
and so will go forth and ruin decor/cost unneccessary cash/invent non-existant remedial works....all a con..as Damian quite rightly pointed out earlier in this nonsense...

It really is crazy mate and the scariest part is like you said they can't understand it which in my view means they shouldn't be in the game.

 

[7029 dave]

It really is crazy mate and the scariest part is like you said they can't understand it which in my view means they shouldn't be in the game.

So electricians that taught me this trade,don't know what their talking about!! (1979) some are proberly not with us any more, and proberly before you was born!!. Close this ****in thread!!

 

[Zeus]

It really is crazy mate and the scariest part is like you said they can't understand it which in my view means they shouldn't be in the game.

I disagree it fills me with a sense of joy to hear people say such stupid stuff cause it means that they will always be creatin work for others that will be far less cheaper cause they haven't quoted to tear the house apart for no reason! Good electricians won't ever have to worry about any recessions!

 

[spark 68]

So electricians that taught me this trade,don't know what their talking about!! (1979) some are proberly not with us any more, and proberly before you was born!!. Close this ****in thread!!

Why ?,

don't you understand it ?

We could have had crap electricians in 1979 who didn't understand it then either lol.

 

[Zeus]

It would appear so and this chap was taught by them!

 

[Ross1]

youre all missing the point !
the OP declared this to be an eicr , therefore the only discussion should about the coding if any.
and IMO its probably a C2 - but a 2 minute fix with a switched fused spur.

Exactly what I have done Biff

 

[richy3333]

Why ?,

don't you understand it ?

We could have had crap electricians in 1979 who didn't understand it then either lol.

Although, wouldn't have had forums then, or computers, or people banging on about Part P, or people banging on about Electrical Trainee, or Aids, or the Olympics in London, or robots. But wine was cheaper

 

[GMES]

So electricians that taught me this trade,don't know what their talking about!! (1979) some are proberly not with us any more, and proberly before you was born!!. Close this ****in thread!!

It doesn't matter who was born when or who taught who, the point is that if you think that you need to rip out a 1.5mm cable to protect it from some magical fault between fcu and the ring then we've all got bigger problems than I thought oh and don't forget to pick your dummy up :53: