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?
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.
G
GLENNSPARK
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...
Take your point but its being feed by 2cable's ie lets say half the load between 2 cables.
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.
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.
G
GLENNSPARK
David...
you need to rethink statements like this ...as they are misleading to the pups in here...
I take the same view as 7029 Dave when approaching similar situations as a good practice measure.
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.
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!!!
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!!!
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.
B
Badged01
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?
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A
AndyL
Going round in circles here, see my earlier post. Fault protection will be supplied via the CB.
B
Badged01
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?
A
AndyL
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
B
Badged01
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!.
Z
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.
B
Badged01
You're being far too serious and stopping us having all this fun and banter to liven up the day
G
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?
an unneccessary nonsense if you ask me
christ, what do some in here think we fuse down for?
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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
prominent, glenn. get a grip, man. :angelsad2:
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