Junction Box and Heat Resistant Cable

[deko]

Hi,

I'm fitting one of these lamps to the upstairs landing...
http://www.thelightingsuperstore.co.uk/product.asp?productid=26541

I currently have a ceiling rose which I am going to replace with a junction box, positioned in the attic. The current circuit is using 1.0mm cable.

My set up will resemble this:

I was going to use the same 1.0mm cable to connect the light fitting to the juntion box, but the diagram above suggests I should be using Heat Resistant Cable.

The light fitting comes supplied with three sleeves that look like this:

http://cableorganizer.com/images/techflex/nomex-lg.jpg

My question is, do I need to use heat resistant cable to connect the light fitting to the circuit or can I use the same 1.0mm cable and just wrap the seperate wires (SL, N, E) in the sleeving inside the light fitting.

The only part of the cable that will be exposed to heat is the bit inside the fitting, and if these 3 wires are sleeved then isn't that safe enough? When you strip the grey sleeving from heat resistant cable, is it still heat resistant?

In the event that I do need to use heat resistant cable, which size should I be using for this installation?

http://www.tlc-direct.co.uk/Main_Index/Cable_Index/Flex_Heat_Resistant/

Many Thanks
d.

 

[Steve]

I dont get it. That light fitting wont get hot in normal use (you can touch a fluorescent tube, it wont burn you). Do you have the fitting? I dont see a reason for heat resistant cable or braided sleeves.

 

[333rocky333]

The choke that works the lamp will reach a high temperature, the heat will build up in the fitting but not always excessive
.
If possible use heat resistant cable, at least the size of the other 1.0 cable
This is 80deg
both inner and outer
if not use butyl flex this is 80 deg also

You can use the same cable as you said and heat sleeve it however over a period of time the cable insulation may still heat up and get brittle.
Usually if the light is on for long hours each day

In all cases route the cable AWAY from the choke which is the long metal thing with the two wires in.
The thinner cable the manufacturer has run to that is rated at over 100deg

I agree a fleur lamp wont always burn you, and not nearly as hot as a bulb,but 2d lamps can get pretty hot IMO and would not reccomend touching one

Later i will post a pic of how hot a 2d lamp can get inside one of those fittings

 

[deko]

Here's some better pics...

The bare fitting
View media item 573
The fiting with 28w bulb
View media item 572
The sleeve covers
View media item 571
The cable from the junction box will come through the hole in the bottom right portion of the fitting, near the connector block and the sticker with the number 4 on it. So only about 40mm if wire will be exposed to any heat.

Once the cover is on, the light is not sealed, there is a gap all the way around, which I hope will alow heat to escape and not too many flies to gather

However, the cable sleeving supplied has a much larger diameter than the wires it will be wrapping, so it'll be loose. If I get the heat resistant cable then I guess it will be a neater job.

The thing is, I don't see 1.0mm heat resistant cable on the tlc website. I see 1.5mm, does this mean it's not used much? Or should I be using 0.75mm?

I see on screwfix two types:

http://www.screwfix.com/prods/14170...at-Resistent/3093Y-1-0mm-3-Core-Heat-Flex-50m

http://www.screwfix.com/prods/12378/Electrical/Cable/Flex/3-Core/3183Y-1-0mm-3-Core-Round-Flex-50m

The only difference I see is one says it's round - so I take it the other one is flat?

Thanks again,

d.

 

[333rocky333]

I do these lights a lot and often find the twin and earth although sleeved it is still baked, however this is in pubs where they are on 14 hours a day

Just the sleeving on twin and earth is usually ok for domestic.
If it is in your own house
You could try that and have a look inside after a few months, if it looks bad then replace it with heat res flex

50 metres will cost a lot
1.5 mm butyl or heat res pvc is used for immersion heaters, and is easier to get, it is bigger than you need, but that should not be a problem really.
It is usually 80 deg inner and outer.
A plumbing shop or the sheds will have cut lengths,you can oversleeve it as well if you want.
If the mcb is 6amp 0.75mm would proberly be ok, but I personally would use 1mm or go bigger at 1.5mm, as you are joining it in a j/box to 1mm

Most flex is round
The ones you looked at one is heat resistant , the other looks like normal flex which is not heat resistant.

ALSO
if you replace that 827 four pin, 28watt , warm white lamp with a 835 four pin,28 watt, white lamp it will be brighter

This is how hot one of them lamps got once before it died, it was a 16watt, smaller than the one you have.
It is rare to get this bad , but they do run hot

Untitled

• 333rocky333
• 11 Apr 2008
• 1

over heated 16w 2d

 

[RF Lighting]

I've never seen the glass go black all the way round

Quite common to find the plastic bit has melted in commercial environments.

 

[333rocky333]

It was in a superdrug , so on at least 12 hours a day.

 

[deko]

Thanks rocky, I'll play it super safe and see if my local supplier has any 1.0mm heat resistant flex AND use the sleeving supplied with the lamp.

Impressive eyesight, you can read the number on the bulb in that pic

 

[333rocky333]

Thanks rocky, I'll play it super safe and see if my local supplier has any 1.0mm heat resistant flex AND use the sleeving supplied with the lamp.

maybe excessive,but once done , then you should not need to worry then.

Once you have finished , leave it on for half hour,
Then carefully touch the outer dome shade , then you can let us know how hot it gets.
You may be suprised

 

[deko]

I'll report in once I've fitted the lights.
Just out of interest, if I were to replace the 28w for a 16w, would the heat output reduce?

 

[333rocky333]

Dont worry too much the fitting should be made to take the heat,
The only weak point would have been the normal pvc supply cable which you have sorted.

The white choke unit inside is designed for a 28w lamp, it will be printed on it, these limit the current to the lamp, a 16w is different to a 28w and different to a 38 w, which is the same physical size as your 28w.

So for a 16 watt lamp you would need to fit a 16 watt choke unit.
If you did want to change it.

You should stick with the right lamp with the right choke really.
A 16 watt would fit, but possibly not last long as the choke would let too much current through to the lamp.

The heat in the fitting will be slightly less, but still there.