Double insulated light fitting [UK] - Page 1
Forum section: electronics / general

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: November 24, 2017, 10:34:34 am
content: Hi,My wife decided to re-decorate the living room. As per usual she perused the typical home furnishing shops of the UK and ended up with some lights fittings which she liked the look of. They are made of metal and have 2 'G9' bulb fitting on a base.I came to fit them, opened the box, looked at the fitting and said 'eh'. I have never seen a metal double insulated light fitting. Not only that we spent quite a lot on these fittings and I expected something of good quality....So DI metal light fittings have a terminal black that is enclosed in a small snap shut plastic box, with sleeving attached on end for the incoming mains supply. Lets just say it would be a major squeeze to get the typical UK mains lighting 'twin and earth' into the sleeving and onto the terminal block.There is a videos online from an online supplier of double insulated light fittings, which shows this kind of sleeving arrangement:What this video doesn't show is that the terminal block and sleeving would end up inside the base of the light, which on a small light fitting is a squeeze.What it also does not explain is in the UK it is typical to have the 'switch loop' which is the junction from Mains supply live to the light switch contacts and back within the light fitting. So how do you do that in that double insulated light?? From what I understand the correct way to do this and comply with wiring regulations in the UK it must be done with a separate junction box. What a pain in the arse just to put a lamp fitting up!There are ways to bodge it such as making your own earth connection on the fitting, remove the double insulated logo, and put a connection block inside the fitting. However this assumes the metal throughout the fitting has a low enough resistance to pass earth bonding tests, and therefore will be able to pass enough current in case of a fault. It’s not the right thing to do really.Has anyone else come across this?Is it common to have say 2-core lead for light fittings in Europe, with perhaps the mains supply feeding into the light switch instead of the light?

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 10:51:41 am
content: Many houses in the UK will not have an earth wire present at the ceiling fixture. So when installing light fittings they either have to be a traditional pendant bulb holder with shade (very old-fashioned!) or a double insulated fitting. If you have a metal fitting which requires an earth connection it becomes a major hassle when no earth wire is present. So IMHO a double insulated fitting that doesn't require an earth connection is far more convenient.Quote from: engineer_in_shorts on November 24, 2017, 10:34:34 amCan you clarify what you mean here? If there are two conductors at the ceiling fixture (no earth wire), then you just connect the two conductors to the light fitting, no? I must be missing something as I don't see the problem.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 24, 2017, 11:12:00 am
content: Here (Germany) we don't have that switch loop. In a modern installation, there's always three wires (L, N, Earth) coming out of the ceiling / wall. In older installations, there may be only two wires (no earth). Most people don't know about double insulation and other issues, so they don't care and just hook up the existing wires to the light fitting and enjoy the new lighting.

author: dmills
author_rank: Super Contributor
timestamp: November 24, 2017, 11:21:08 am
content: Usual domestic practise here is to run a line from the breaker box to the first room, then loop it to the next and so on, switches are wired up to the ceiling rose where they are connected in the obvious way.The obvious issue is that doing this gives you either 6 (No earth, you still see it sometimes) or 9 wires to connect in the ceiling rose, not a problem until you replace the pendant with something screwed to the ceiling and not designed for it.The final bit of fun is that our wiring regs insist that any junction box must be accessible (sensible really), so burying a junction inside the ceiling is unacceptable.

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: November 24, 2017, 11:31:34 am
content: Quote from: IanB on November 24, 2017, 10:51:41 amNot really.1. I would say it's not really common to not have an earth:Lighting circuits installed before 1966 often did not have an earth. Since 1998 it has been a regulation requirement that it MUST have an earth. Therefore if you had a house built in the 60's or earlier and has not been rewired, there may well be no earth. This is approx 65% of houses in UK. However if since 1998 the lighting circuit was touched by a professional electrician it really should have been upgraded, and now if an electrician touches the circuit i believe itmustbe upgraded for him to sign a part P certificate (for whatever that's worth). Also if you were say renting the house out I believe there is some statuary requirements to get a safety check to regulations. I think there is around 20% of the houses in the UK are rental.2. If you have a light fitting which is double insulated you should not be using that light fitting as a junction, so where do you put:- the junction for mains supply live to switch (switch loop)?- the junction of incoming mains supply (Live, neutral and earth conductor) to the outgoing mains supply to the next light on the circuit?Quote from: IanB on November 24, 2017, 10:51:41 amI quickly found this which should explain:www.diyhowto.co.uk/projects/one-way-lighting-loop-in.htm

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 11:45:08 am
content: Quote from: engineer_in_shorts on November 24, 2017, 11:31:34 amI see. So the main lighting circuit is at the ceiling rose with a spur out to the light switch. I had a mental picture of the lighting circuit running through the switch at the wall with a spur up to the light fitting. Now it makes sense. (Especially now I think about it. Much easier to run the lighting circuit between the joists in the ceiling than through the solid walls.)QuoteQuoteThat (up to 65%) seems rather common to me?QuoteSince houses of that period (60's or earlier) are invariably of brick construction with breeze block inner walls and buried wires, the cost and disruption of rewiring should not be underestimated. I know old wiring "should" be upgraded, but there is a reason why in many cases it has not been done...

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: November 24, 2017, 11:47:40 am
content: Quote from: dmills on November 24, 2017, 11:21:08 amWe have quite a few roses with 4 cables (12 wires)1. Mains supply feed to this light.2. Mains out to feed next light.3. Switch loop.4. Loop to other light.At least it's not dual switched!!

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: November 24, 2017, 11:51:01 am
content: Quote from: IanB on November 24, 2017, 11:45:08 amI think that's why it has now changed to a must, people have had 20years to get it right.

author: coppice
author_rank: Super Contributor
timestamp: November 24, 2017, 11:57:37 am
content: Quote from: IanB on November 24, 2017, 11:45:08 amMost 1960s houses in the UK are built from 2 layers of bricks, with a cavity and tie bars between the layers. A lot of those cavities have now been filled with injected foam. By the 80s this had largely migrated to a layer of bricks, a filled cavity and a layer of aerated concrete blocks. Many houses built with a waterproof rendering on the outside were built with a single layer of 200mm thick aerated concrete blocks in the 80s.Who ever built from breeze blocks? They have so little strength they are only suitable for infill without a structural frame.

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 12:02:51 pm
content: Quote from: coppice on November 24, 2017, 11:57:37 amProbably incorrect use of the term. I mean concrete blocks or cinder blocks presumably. The outer wall of the house is constructed from clay bricks, the inner walls and dividing walls from a low cost grey block of some kind. I always heard it called breeze block but apparently that is not what they are. Today I learned...

author: coppice
author_rank: Super Contributor
timestamp: November 24, 2017, 12:06:33 pm
content: Quote from: engineer_in_shorts on November 24, 2017, 11:31:34 amWhere does the date 1966 come from? My experience of late 50s houses in London is they mostly had earth throughout the wiring. The problems come with metal conduited wiring, which seemed to be in vogue in the 60s, where the earth might be the steel conduit, and the connections between section might be rather iffy.

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 12:10:28 pm
content: Quote from: coppice on November 24, 2017, 12:06:33 pmThe house I grew up in (built ca. 1960) had no earth in the lighting circuits.

author: coppice
author_rank: Super Contributor
timestamp: November 24, 2017, 12:20:09 pm
content: Quote from: IanB on November 24, 2017, 12:02:51 pmI must apologise. I googled "breeze block" to find a picture of a 1960s breeze block to show what they were. It seems people are now applying that term to aerated concrete blocks, so you were actually correct. Even the online dictionaries now define a breeze block as an aerated concrete block.A real 1960s breeze block is a very low density block, made of a very open weave of wood strands, sprayed over with cement. They made a low density filler with good thermal insulation, but little strength. I believe aerated concrete blocks were common in a lot of mainland Europe since the 1930s, but I never saw one in the UK until about 1970.Aerated concrete blocks do have cost benefits over brick, but the main reason for their use these days is their reasonably good thermal insulation properties.

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: November 24, 2017, 12:30:48 pm
content: Quote from: coppice on November 24, 2017, 12:06:33 pmI found this on IET message boards:http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=22102QuoteBut i cannot find an online copy of 14th edition wiring (1966).

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: November 24, 2017, 03:35:27 pm
content: stuff one of these up in to the ceiling above your light fitting to house all your loop wiring, then you just have a L,N&E flex going to your actual light fitting.Hopefully your fitting is big enough to hide the hole. These are usually used for downlighters.https://www.screwfix.com/p/wagobox-light-junction-box/8423F

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: November 24, 2017, 03:54:41 pm
content: Quote from: DenzilPenberthy on November 24, 2017, 03:35:27 pmNo:- If you did that, you wouldn't have anything to screw the holding bracket against, unlike a downlight.- And this is a wall lamp, not a ceiling one.attached picture