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Topic Title: Lighting cable
Topic Summary: 1.5 & 1.0mm
Created On: 10 January 2019 08:18 PM
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 10 January 2019 08:18 PM
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mikejumper

Posts: 2810
Joined: 14 December 2006

I'm surprised by the number of installations I come across where 1.5mm T&E has been used for lighting circuits protected by a 6 Amp MCB.

Why, in relatively small domestic installations, would you use a cable nominally rated at 18 Amps for a circuit that most of the time is probably only drawing an amp or two. It wastes copper, makes termination more awkward and costs more.
 10 January 2019 08:28 PM
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broadgage

Posts: 3170
Joined: 07 August 2007

I agree.
1.5mm would be a better choice for unusually long circuits to reduce voltage drop.
1.5mm would be better for 10 amp circuits to allow for de-rating if grouped or in thermal insulation.

But for modest length 6 amp circuits it seems extravagant to use 1.5mm.

1.5mm is now the minimum permitted for "power circuits" and some take the cautious view that connection of a fart fan or bell transformer turns a lighting circuit into a power circuit and thus requires 1.5mm.
 10 January 2019 08:35 PM
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RB1981

Posts: 513
Joined: 16 September 2007

I completely agree.

However it is always done that way here - in fact wholesalers don't even stock 1mm^2 cable and it would have to be specially ordered (and likely cost more than 1.5mm^2).

I never understand why, if taking that approach, they don't at least use 10A circuit breakers.

Across the border 1.5mm^2 is the minimum permitted cross-sectional area for non-flexible cables for lighting & power, however at least they use 10A MCBs (ET101 still defines them as MCBs) rather than the nonsense in the north of putting it on 6A circuit breakers.

-------------------------
Walsh Electrical Services
http://www.walshelectrical.ie/
RECI REC & NICEIC Approved Contractor
 10 January 2019 10:37 PM
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aligarjon

Posts: 4053
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1.0mm is readily available around here thankfully. I have rarely used 1.5mm, just on long circuits, which is rare for domestics.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 10 January 2019 10:46 PM
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chrispearson

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Originally posted by: mikejumper

I'm surprised by the number of installations I come across where 1.5mm T&E has been used for lighting circuits protected by a 6 Amp MCB.

Why, in relatively small domestic installations, would you use a cable nominally rated at 18 Amps for a circuit that most of the time is probably only drawing an amp or two. It wastes copper, makes termination more awkward and costs more.


You wouldn't, although terminating 1.5 sqmm is hardly difficult. However, I agree that 33% of the copper is wasted, which is not 'green' especially with modern LED luminaires.
Originally posted by: RB1981

However it is always done that way here - in fact wholesalers don't even stock 1mm^2 cable and it would have to be specially ordered (and likely cost more than 1.5mm^2).


I don't know about T & E, but that is the minimum size for singles.
 10 January 2019 11:08 PM
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RB1981

Posts: 513
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Originally posted by: chrispearson
I don't know about T & E, but that is the minimum size for singles.


Not so much the minimum size as the minimum size available. 1mm^2 singles on a lighting circuit would be compliant, but good luck sourcing them.

-------------------------
Walsh Electrical Services
http://www.walshelectrical.ie/
RECI REC & NICEIC Approved Contractor
 10 January 2019 11:58 PM
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mapj1

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i presume your 1.5mm2 T and E has a full size insulated CPC as well , so can supply a few sockets.

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regards Mike
 11 January 2019 12:11 AM
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RB1981

Posts: 513
Joined: 16 September 2007

Originally posted by: mapj1

i presume your 1.5mm2 T and E has a full size insulated CPC as well , so can supply a few sockets.


In the north it is just the ordinary 6242Y cable, so no.

In the south the cable to I.S. 201 does indeed have a full-sized, insulated cpc though. Needless to say the Irish Standard cable costs me substantially more than the British Standard equivalent.

It certainly wouldn't be normal practice to use the 1.5mm^2 to supply socket outlets though!

-------------------------
Walsh Electrical Services
http://www.walshelectrical.ie/
RECI REC & NICEIC Approved Contractor
 11 January 2019 05:40 AM
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dustydazzler

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1.5 for sochets

You cheeky badgers
 11 January 2019 07:11 AM
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broadgage

Posts: 3170
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Of course in work places with a long hour lighting load, larger cables might pay for themselves via reduced losses.

Consider as an example a 1kW lighting circuit in which the losses are reduced from 3% to 2% by use of larger cable.

Saving 1% is 10 watts, or perhaps 50Kwh a year for long hours of use. 50Kwh is worth about £7.50.
In twenty years and presuming no increases in energy cost, £150 has been saved, more than enough to pay for larger cables.
 11 January 2019 08:41 AM
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Zoomup

Posts: 6117
Joined: 20 February 2014

1.0mm2 T&E is more than adequate for domestic lighting circuits these days, especially considering that we are changing our lighting to more energy efficient types. )But even with old filamment lamps it was still o.k.). 1.5mm2 is a waste of money for most domestic lighting jobs. I have never found difficulty in obtaining 1.0mm2 T&E cable.

Z.
 11 January 2019 08:53 AM
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dustydazzler

Posts: 3068
Joined: 19 January 2016

I personally used to exclusively use 1mm on my own jobs , I just found it much nicer to terminate in those fancy wall lights and flush fittings etc

But when I subbied would often be given rolls of 1.5 to wire the lights in new builds etc

Not my money so never really questioned it
 11 January 2019 08:55 AM
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Blencathra

Posts: 219
Joined: 07 November 2017

When I was rewiring council estates, the spec was 1.5 for lighting & 16mm tails
 11 January 2019 09:01 AM
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dustydazzler

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Yes 16mm were extremely common in my area
 11 January 2019 09:15 AM
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mapj1

Posts: 12039
Joined: 22 July 2004

well from a currant carrying perspective ('ampacity' to our friends with a funny accent, the welsh...) modern double insulated LED lights could probably be wired in speaker flex.
But there is another problem, that of being robust against mice in the loft or Dangerous Dave's DIY, so a minimum has to be agreed, it just happens that different local styles have emerged as to what that is.
I don't really have a problem with a 13A socket or a 16A radial on 1.5mm clipped direct, and it does side step this question about things like bathroom fans and mirror heaters and so forth not being 'lighting circuits'.

-------------------------
regards Mike
 11 January 2019 09:31 AM
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sparkingchip

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Joined: 18 January 2003

Cost difference around a fiver per small house?

Andy B
 11 January 2019 09:51 AM
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Zoomup

Posts: 6117
Joined: 20 February 2014

Originally posted by: Blencathra

When I was rewiring council estates, the spec was 1.5 for lighting & 16mm tails


Yep, there was a perceived potential abuse of lighting circuits so 1.5mm2 was specified. Possibly to be more robust when aluminium kitchen foil was wrapped around a blown cartidge fuse in the fuse box.

Z.
 11 January 2019 09:53 AM
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Zoomup

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Joined: 20 February 2014

Cost in extra time fiddling about with the bigger conductors, substantial.

Z.
 11 January 2019 09:59 AM
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pww235

Posts: 252
Joined: 03 April 2014

Is it really that much of a difference Z? ~0.2mm difference in core diameter.

P
 11 January 2019 10:06 AM
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Zoomup

Posts: 6117
Joined: 20 February 2014

Originally posted by: pww235

Is it really that much of a difference Z? ~0.2mm difference in core diameter.



P


I notice a difference. The 1.5mm2 fights back and is more difficult to dress into back boxes. Also 1.0mm2 is easier when connecting two conductors into switch terminals such as with two-way switching. It is just a personal choice for me. And 1.5mm2 three core and earth cable is less manageable than 1.0mm2 three core and earth. Why use a cable bigger than needed?

Z.
IET » Wiring and the regulations » Lighting cable

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