Earthing metal framed down lights.


Postby peterlos » Thu Jun 05, 2008 1:06 am

Have a system of down lights with 50 Watt dichroic lamps inserted; 4 lamp circuits with 2 to three lamps per circuit, so not many. I was recently advised to earth the lights, which I did in daisy chain fashion with 2.5 sq mm single flex. I made patent contact with the frames for each light. There is no proprietary earth lug installed, so it’s makeshift.
On close re-inspection, four weeks later, I noticed some slight melting of the PVC at the closest point of the flex to the light (maybe 5mm of exposed copper at installation). I immediately removed all the earthing wire and need to rethink the earthing installation.
I looked again at lamps available in the stores and really they are all essentially the same. None I saw had earth connection facility provided. I know installation of some lamps are an electricians challenge but wondering if any here have some practical advice even to the point of rethinking the whole installation. I simply don’t want a fire and even though there’s no requirement in this country for this safety assurance, I know that it’s a sensible thing.
peterlos
Posts: 4
Joined: Mon Apr 21, 2008 2:04 pm

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Postby ericmark » Thu Jun 05, 2008 12:52 pm

You have raised a number of points:-
• SELV or Double insulated lamps do not require earths and in fact it is expressly forbidden on SELV (Separated Extra Low Voltage i.e. 12 volt). Double insulated items have a double square one inside the other.
• Min size for earth wire not mechanical protected i.e. not a core of a multi-core cable is 4mm²
• Table 55.2 lists a lot of signs found on luminaires giving mounting details concerning temperature sorry no pictures allowed this may mean special cable is required. This in essence means follow manufactures instructions.
Since we do not know exactly what lamps you have it is a little hard to give hard and fast advice but dichroic lamps would normally have a triangle with apex to bottom with an F crossed out to say suitable for “direct mounting on non-combustible surfaces onlyâ€
ericmark


Postby peterlos » Thu Jun 05, 2008 4:00 pm

[quote="ericmark"]You have raised a number of points:-
• SELV or Double insulated lamps do not require earths and in fact it is expressly forbidden on SELV (Separated Extra Low Voltage i.e. 12 volt). Double insulated items have a double square one inside the other.
• Min size for earth wire not mechanical protected i.e. not a core of a multi-core cable is 4mm²
• Table 55.2 lists a lot of signs found on luminaires giving mounting details concerning temperature sorry no pictures allowed this may mean special cable is required. This in essence means follow manufactures instructions.
Since we do not know exactly what lamps you have it is a little hard to give hard and fast advice but dichroic lamps would normally have a triangle with apex to bottom with an F crossed out to say suitable for “direct mounting on non-combustible surfaces onlyâ€
peterlos
Posts: 4
Joined: Mon Apr 21, 2008 2:04 pm


Postby ericmark » Thu Jun 05, 2008 6:49 pm

Twin & Earth 624B 300/500V BS7211 XLPE/LSZH Low Smoke
318B LSZH insulated/LSZH sheathed 300/500V to HO5Z1Z1-F
309Y Heat Resistant PVC insulated & sheathed 300/500V to BS6500
To name but three i.e. cable able to stand some heat. 1.5mm² is good enough and I have not seen any 5mm² so wonder if your looking at diameter rather than cross sectional area. Most rubber like cables rather than PVC can stand more heat than PVC in screwfix 3183TQ 1.5mm 3 Core Heat Flex Quote No: 27005 would fit the bill. I am so surprised that any fitting requiring an earth does not have provision for one. Look at screwfix Quote No: 19324 and it states “Max. lamp rating 50W. Double insulated ceramic lamp holder. Cut-out dimension 65mm. CE approved (BS EN 60598). Suitable for GU10 or GZ10 aluminium or dichroic reflector lamps, sold separately (Quote 25367 or 99333).â€
ericmark


Postby peterlos » Thu Jun 05, 2008 8:26 pm

Thanks again Ericmarc,

A problem here is electrical standards. There's a code but no-one has seen it. There are very dodgy appliances available even by well known leading brands: metal cased kettles, rice steamers and so on. You can buy these today without any provision for earthing. In fact I wrote to one international manufacturer to find out how to earth a hot water kettle. He gave me the specs but finished by saying that it wasn't made to be earthed and it was complaint with this countries standards. I've had hot water shower heaters installed with RCD's requested. I checked 12 months later. The earth had been wrapped around a re-inforcing rod on a concrete column of the house. Typically fridges are sold with two core cable in this case the earth has been removed. Product quality comes down to price. You can't see the benefits of earthing, many products don't have it so why is it needed... this really is a common belief

Most domestic dwellings don't have earthing facilities available. I've had 2 inch nails driven into the concrete pavement by installers as an earth for an air-conditioner. Cable conventions are ad-hoc in practice. The colour standard is Black for phase, white or grey for Neutral and Green (if you're lucky) for Earth. In this house the first attachment to the incoming power lines had reversed the colours..... and the earthing system is PME/MEN!

The Europeans, British, Australians and New Zealanders have great standards and some are trying to use these as a guide to safe electrical wiring and installation. We do have to compromise because some items are not available or are of poor quality. Testing isn't available by electricians or the power authorities. Some people are improvising well and are showing initiative simply to be safe. It's forums like this that really can add a new level of information and understanding.

I will go down to the electrical trade supplier and ask about the cables and show them a picture of the lamp your illustrating. A lot of cables come from China and a few from SE Asia.That can be a beginning.

You've really helped a lot.
peterlos
Posts: 4
Joined: Mon Apr 21, 2008 2:04 pm


Postby ericmark » Fri Jun 06, 2008 10:32 am

From your reply I think your in the US this is a British site and everything I have said is assuming a British system.
As to earths we call it Class 2 or Double insulated where we don't require any earth wire and it can still have metal parts.
In the US you I think have a split phase supply to houses where we use a single phase supply. Your lights are supplied direct from the switch where we take power to the light first then the switch. The screws colours on switches show what they are for where we have L1 L2 and Com marked and what we call 2 way switching you call 3 way switching and again wired completely different.
Also as to earthing dry areas will have different requirements to wet, and also where you have many electrical storms earthing arrangements also change.
I would advise you use a local forum as you may get completely the wrong advice if you are not in the UK.
ericmark


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