Fitting downlighters in rockwool-insulated ceiling

Hi
I'm thinking of installing some in the upstairs bathroom; which is plasterboard with a thick layer of Rockwool on top.
I know from experience how much heat is chucked out from the downlighters fitted in my kitched ceiling. So what's the correct procedure for an upstairs ceiling? I'm sure there would be a fire risk if I just left the layer of insulation untouched; yet to cut a large circular hole in it around the light fitting would I'm sure be very wasteful of heat when the lights are off.
I'm envisaging maybe I need to nail a plasterboard 'bridge' spanning the joists adjacent to each light, and then running the Rockwool over that, thereby leaving an airgap above the fitting. Is that appropriate /OTT /inadequate?
Thanks David
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Its suggested by the manufactures to cut a circle of rockwool around the downlighters. As for the heat loss I think it will be negligible unless you are planning on installing hundreds of them, Also the back of the lights is I think meant to be clear for about 10-20 cm
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You need to construct a small box with air holes to fit over the back of the fitment because in the future someone might otherwise disturb the rockwool and thus cause a fire hazard.
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Why the airholes? and what's wrong with an upturned clay flower pot?
--
David

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snipped-for-privacy@chaplehouse.demon.co.uk wrote:

You have to get rid of the heat somehow to avoid the cavity getting hot enough to melt wiring insulation.
Heat will be lost via the plasterboard into the room, and upwards through the flowerpot base - holes in it help if teh pot top pokes through the insulation.
Experience shows a simple void of a sqaure foot or so is enough to leak heat down through the plasterboard, but rockwool wrapped transformers will fail :-)
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writes

The type that I have use a heat resistant cable closest to the lamp and the transformer is outside of the flowerpot with the cable going through the hole in the bottom of the pot (which is now the top IYSWIM) I have felt the pots a number of times and whilst it is warm I wouldn't call it hot. The only one that I have where I have thought about heat dissipation is the shower one which has a sealed lens but this is no hotter than the others.
--
David

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you
is
Best install a plantpot over and seal with silicon sealing. A decent sized one will do, with a bit of air in there.
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The heat loss is highly significant.
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hi guys...
just new to diy and to this site so go easy please....
ive read about this 'transformer' for the last posts... im planning o putting four downlighters into the hallway of our house and als wondered if i could run them from the orignal light fitting.. i tak note of the plant pot idea and will do that... so not to set the hous on fire....
what exactly is this transformer? and where would i purchase one from and what is the best way to wire these things up so it can be ran fro the exisiting single wire.. many thanks
any help would be great
Crai
-- cjbeattie
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cjbeattie wrote:

Hi!
Will try.. ;-)

OK downlights come in two basic flavours, mains ones and 12V ones. The mains ones, as the name suggests, run directly from the mains and don't need a transformer. The 12V ones need something to step down the mains voltage to 12V. This is traditionally a transformer. Also readily available are so called "electronic transformers" which are smaller and lighter but do the same job.
If you go the mains route then you simply need to replace the existing ceiling rose with a junction box and wire out from there to each light position. You can use a combination of "star" wiring, or daisy chain, whichever is simplest.
With a transformer you can do it the same way and have a small transformer for each light fitting, or you can use a bigger one that can run several lights at once. Note however you are better off keeping the 12V cables short, and they will often need to be quite heavy wire to cope with the extra current (if you keep the power the same, but reduce the voltage the current must go up to compensate).
So on the face of it you may think mains downlights are simpler since they are easy to fit, however they are the inferior solution in many ways:
12V will give you more light for the same power, a whiter more natural light, longer lasting, cheaper, and more robust bulbs, and the option of using dichroic bulbs[1].
[1] dichroic bulbs have a semi silvered reflector built in, that allows some of the infrared energy to pass through the reflector and out of the back of the bulb. This means they give a better colour of light and throw far less heat forward to whatever they are illuminating (although the fitting itself will run hotter).
--
Cheers,

John.

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cjbeattie wrote:
Oh, forgot to say

http://www.tlc-direct.co.uk/Main_Index/Lighting_Menu_Index/Lighting_Downlights_Index/Lighting_Transformers/index.html
http://www.screwfix.com/app/sfd/cat/cat.jsp?ts 061&id1667
--
Cheers,

John.

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ok john
thanks for the tips....
i understand a wee bit better now...
i bascially inherited the house from my mam & dad who passed away las year and suffice to say nothing has been done for around 10 years....
im very very new to diy hence the statement (go easy)
I bought the downlighters from wickes... and i think from you have sai that they are indeed the ones you can wire into the mains... so this will do...
I was thinking of using the original ceailing output... which i wil plaster over when finished and then splitting the wires into 4 way (via a junction terminal) and then changing the bulbs from 50w down t 20w (ive read quite a bit on heat etc from 50w bulbs) anyways this wil keep within the 100w i presume that the hall light had in the firs place....the cavity between the floors... where the lights will be i quite small its a prewar (ex council house) and hence the old design. the gap is only around half a foot... still enough i hope for th downlighters because ive bought the bloody things now lol...
anyways the lights i have like i said are from wickes and on the box i says...
WICKES 4 Mains Halogen Round fixed downlights
i presume (and hope) these ones will be ok to wire direct.... i wil also use the plant pot idea for the heat dispersion of the untils whe under the floor boards.... i assume they mean REAL CLAY plant pots yes as plastic would melt...
you said "If you go the mains route then you simply need to replace th existing ceiling rose with a junction box and wire out from there to each light position. You can use a combination of "star" wiring, or daisy chain, whichever is simplest."
forgive me for being ignorant but what is a junction box exactly? (i it a terminal block connector? will that suffice? and what is a sta wiring or daisy chain wiring? thanks... i think i will go down th mains wiring option
anyways thanks for the help john:) (probaly saved me from burning m house down lol)
Craig
ps....if you have msn messenger then please feel free to add me.. min is ***Katncraig86 (AT) hotmail.com********
then i will have a online guro if i need one:)
once again thanks:
-- cjbeattie
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cjbeattie wrote:

Yup that ought to be OK. A couple of things to check though.
Firstly most mains downlighters are metal bodied and hence must be connected to an earthed lighting circuit. There is a small possibility if the house wiring is very old that it is not earthed. Looking at the cables will tell you. Modern cable will have two insulated wires in it (typically red and black in your case) plus a third bare wire.
If you are missing the earth wire then *do not* inttall the downlighters unless they are marked as "double isolated" (the double isolated logo is two small concentric square boxes).

OK they probably take bulbs of type GU10 then. These are ok for direct connection to the mains. You will get to know that bulb number well! ;-)

Yup, your traditional clay/terracotta jobbie.

It looks like this: (also available in brown)
http://www.screwfix.com/app/sfd/cat/pro.jsp?id 802&tsc625
Note this is a four terminal box[2]

Star wiring is where you run a separate wire from the junction box to each light. So if you have four lights there are four wires coming from the junction box - one to each light.
Daisy chain is where you run from the JB to the first light, and thence the second and third and fourth. You could also use some combination of the two if required[1].

Hopefully it is fused or has a micro circuit breaker somewhere which ought to stop that happening!

If you post here there you will usually get a quick answer since there are plenty of folks in this newsgroup well able to answer these sorts of questions.
[1] Running wires in ceilings is easy if they run in the same direction as the joists - you can do it all from the ceiling side. If however you need to run across the joists then you need to lift floorboards in the room above so that you can drill holes through the middle of the joists for the wires (don't put holes near the top or bottom of the joist since that not only weakens the joist but also makes the cable vulnerable to damage from nails and screws etc). Hence it is often easier to use a combination of star and daisy chain wiring to minimise the difficult cable runs across the joists. e.g.
Original Room/light position
====================================| | | | |-----------------------------------| <--- joists | | | | |-----------------------------------| | L | | | |-----------------------------------| | | | | ==================================== New lighting using a mixture of star and daisy chain wiring:
====================================| | | L1----------------------L2 | |-----------------------------|-----| <--- joists | | | | | | |-----------------------------|-----| | ------------JB----------+ | <- two cables leave JB | | | |-----|-----------------------------| | L3----------------------L4 | <- cable daisy chained | | ==================================== [4] Most lighting wiring is wired using the "loop in" method. That will mean that when you look at a ceiling rose you may be surprised how many wires there are! There will be a cable bringing power (comes from the previous light in the circuit), and another taking it out again (to the next light), plus one more to the switch. This gives you nine individual wires to play with and another two connecting to the light pendant. You will need to transfer these to a junction box and wire the new lights such that they are connected where the pendant is currently connected.
--
Cheers,

John.

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hi john
thanks for the prompt reply:)
ok i will do exactly that what you suggested... and yes the lights hav double sign thingy you mentioned:) so dont worry about earth...
i was wondering though..
after thought i realised my hallway is quite big really and since i downgrading the lights all down to 20w..
would it be ok to run 6 in total off the original lighting source instead of 4.. like i said the post before...
i said i was downsizing all the bulbs to 20... MUST i do this? or wil the system still take 6 - 50w downlighters? As you can probaly tell i a complete noob to electrics... hence what are to you probaly stupi questions... we all goto learn somewhere i guess...
anyways...if you could answer the above posts that would be great;)
thanks for all your help....
Crai
-- cjbeattie
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cjbeattie wrote:

Well if it is there, wire it up correctly as you go. When you get to a light fitting that does not require it, just slip some green yellow sleaving over it and fold it back rather than cutting it off - you never know when someone will change a fitting in the future adn find they need it.

As long as you don't exceed the rating of the circuit you are fine. Most lighting circuits are protected by a 6A MCB these days which gives you at least 1380W to play with. Go round and count up how much is already on the circuit. For every light position that is less than 100W, count it as 100W, for any that are more count them as their actual value.

6 x 50 = 300W probably fine unless the circuit is allready highly loaded.

The only stupid question is the one you don't ask, as they say!
--
Cheers,

John.

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Other posters to this group have previously suggested putting terracotta plantpots over the light fittings, & cut the rockwool to fit round the plantpot.
--
Tim Mitchell

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On Fri, 23 Jan 2004 11:27:09 +0000, Tim Mitchell

TLC Direct sell commercial downlighter covers which appear to have these sorts of characteristics:
http://tinyurl.com/34r6g
PoP
Sending email to my published email address isn't guaranteed to reach me.
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Bit more expensive than a flowerpot! But then they are designed to restore ceiling fire resistance for commercial use; I'd think they were OTT for domestic
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to this group have previously suggested putting terracotta

That's what I did a little under two years ago and all seems to be running fine. If I remember correctly the flowerpots were about 12" diameter and 6" deep. Rather confused the assistant in the local garden center though:
Assistant: Do you need any help? Me: No, not really. Just trying to decide what size I need. Assistant: What are you going to be putting in them? Me: Bulbs. Assistant: What type of bulbs? Me: 35W Halogen.
I replaced the fibre glass around the upturned pot. From what I remember the electronic transformer is under the fibre glass and I haven't had any problems.
Andrew
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On 26 Jan 2004 09:38:50 -0800, andrew_d snipped-for-privacy@hotmail.com (Andrew May) wrote:

Although they might not fail immediately they will fail prematurely. Also depends whether the transformers have self diagnostic circuits in or just bog standard cheapy ones.
SJW A.C.S. Ltd.
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