Author Topic: Double insulated light fitting [UK]  (Read 5740 times)

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Offline engineer_in_shortsTopic starter

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Double insulated light fitting [UK]
« on: November 24, 2017, 10:34:34 am »
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?
« Last Edit: November 24, 2017, 10:36:47 am by engineer_in_shorts »
 

Offline IanB

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Re: Double insulated light fitting [UK]
« Reply #1 on: November 24, 2017, 10:51:41 am »
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.

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!

Can 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.
« Last Edit: November 24, 2017, 10:55:21 am by IanB »
 

Offline capt bullshot

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Re: Double insulated light fitting [UK]
« Reply #2 on: November 24, 2017, 11:12:00 am »
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.
Safety devices hinder evolution
 

Offline dmills

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Re: Double insulated light fitting [UK]
« Reply #3 on: November 24, 2017, 11:21:08 am »
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.   
 

Offline engineer_in_shortsTopic starter

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Re: Double insulated light fitting [UK]
« Reply #4 on: November 24, 2017, 11:31:34 am »
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.

Not 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 it must be 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?

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!

Can 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.

I quickly found this which should explain:
www.diyhowto.co.uk/projects/one-way-lighting-loop-in.htm
 

Offline IanB

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Re: Double insulated light fitting [UK]
« Reply #5 on: November 24, 2017, 11:45:08 am »
I quickly found this which should explain:
www.diyhowto.co.uk/projects/one-way-lighting-loop-in.htm

I 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.)

Quote
I would say it's not really common to not have an earth

Quote
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.

That (up to 65%) seems rather common to me?

Quote
However if since 1998 the lighting circuit was touched by a professional electrician it really should have been upgraded

Since 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...



 

Offline engineer_in_shortsTopic starter

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Re: Double insulated light fitting [UK]
« Reply #6 on: November 24, 2017, 11:47:40 am »
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.

We 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!!
« Last Edit: November 24, 2017, 12:01:44 pm by engineer_in_shorts »
 

Offline engineer_in_shortsTopic starter

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Re: Double insulated light fitting [UK]
« Reply #7 on: November 24, 2017, 11:51:01 am »
Since 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...
I think that's why it has now changed to a must, people have had 20years to get it right. 
 

Offline coppice

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Re: Double insulated light fitting [UK]
« Reply #8 on: November 24, 2017, 11:57:37 am »
Since 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...
Most 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.
 

Offline IanB

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Re: Double insulated light fitting [UK]
« Reply #9 on: November 24, 2017, 12:02:51 pm »
Who ever built from breeze blocks? They have so little strength they are only suitable for infill without a structural frame.

Probably 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...
 

Offline coppice

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Re: Double insulated light fitting [UK]
« Reply #10 on: November 24, 2017, 12:06:33 pm »
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 it must be 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.
Where 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.
 

Offline IanB

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Re: Double insulated light fitting [UK]
« Reply #11 on: November 24, 2017, 12:10:28 pm »
Where 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.

The house I grew up in (built ca. 1960) had no earth in the lighting circuits.
 

Offline coppice

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Re: Double insulated light fitting [UK]
« Reply #12 on: November 24, 2017, 12:20:09 pm »
Who ever built from breeze blocks? They have so little strength they are only suitable for infill without a structural frame.

Probably 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...
I 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.
 

Offline engineer_in_shortsTopic starter

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Re: Double insulated light fitting [UK]
« Reply #13 on: November 24, 2017, 12:30:48 pm »
Where does the date 1966 come from?

I found this on IET message boards:
http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=22102

Quote
The 14th edition (1966) was the first to specify earths throughout every lighting circuit:

D.6 At every lighting point an earthing terminal shall be provided and connected to the earth-continuity conductor of the final sub-circuit.

D.7 An earthing terminal, connected to the earth-continuity conductor of the final sub-circuit, shall be provided at every lighting switch position unless this takes the form of an earthed metal box having a means of fixing the switch-plate in reliable electrical contact with the box.

NOTE.- Regulations D.6 and D.7 are applicable even where a point or switch position is intended, at the time of installation, for the attachment of an all-insulated accessory or fitting or a double-insulated fitting. They are intended to allow for any later substitution of an accessory or fitting which needs to be earthed.

However, metal switch plates on unearthed lighting circuits did not comply even before the 14th edition.

But i cannot find an online copy of 14th edition wiring (1966).
 

Offline DenzilPenberthy

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Re: Double insulated light fitting [UK]
« Reply #14 on: November 24, 2017, 03:35:27 pm »
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
 

Offline engineer_in_shortsTopic starter

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Re: Double insulated light fitting [UK]
« Reply #15 on: November 24, 2017, 03:54:41 pm »
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

No:
- 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
 


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