[cough]pyro[/cough]
chase concrete ceiling for 1mm csa lighting?
- Thread starter mgx
- Start date
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painted white?
If you like, or you could use pyro with a white sheath
For what it's worth, I figured out how to solve this and avoid the problem of running electrical wiring in the ceiling altogether. Might be useful for anyone else who has my problem.
Turns out my ceiling has a small layer (~5mm max) of plaster.
Decided to use 12v fittings all over, so I can keep the transformers in the wall (in the kitchen, they are in a small void behind the fridge, and in the living room, they are within a void behind a 2gang accessory box w/ blank plate). I run 12v cable (15a rated) up the wall then across the ceiling buried in the plaster skim, then it comes out at the light roses (living room) or behind bulkhead (kitchen).
For the living room they are two fittings, each having 15x 10 G4, i.e. 150w each (one pair 15a cable each). In the kitchen there are six fittings, each with 2x max 50w AR111, switched in two banks, so four pair 15a cable each (though this is right at the cable rating, so may need to use 35w lamps).
Also doing the same with some alarm cable feeding fire detectors in the living room, and in the kitchen bulkhead. Stripped back the outer sheath, glue cables in small trench, pollyfilla over them.
I'm pretty happy now.
Turns out my ceiling has a small layer (~5mm max) of plaster.
Decided to use 12v fittings all over, so I can keep the transformers in the wall (in the kitchen, they are in a small void behind the fridge, and in the living room, they are within a void behind a 2gang accessory box w/ blank plate). I run 12v cable (15a rated) up the wall then across the ceiling buried in the plaster skim, then it comes out at the light roses (living room) or behind bulkhead (kitchen).
For the living room they are two fittings, each having 15x 10 G4, i.e. 150w each (one pair 15a cable each). In the kitchen there are six fittings, each with 2x max 50w AR111, switched in two banks, so four pair 15a cable each (though this is right at the cable rating, so may need to use 35w lamps).
Also doing the same with some alarm cable feeding fire detectors in the living room, and in the kitchen bulkhead. Stripped back the outer sheath, glue cables in small trench, pollyfilla over them.
I'm pretty happy now
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Okay, I'm willing to listen.
In terms of the alarm cable, what is wrong with stripping the outer sheath for about 30-50cm? The inner cores are still twisted, I needed to strip the sheath because the plaster is not thick enough for sheathed 8core cable. I have done the alarm cable.
For the 12v cable: I actually haven't done this yet. What is the issue with cable length between transformer and light? I have other cases (e.g. PoE and cctv) where 12v is run over a longer distance? I know I will get some voltage drop. I actually intend to test the configuration to ensure voltage drop is acceptable before installing.
In terms of the alarm cable, what is wrong with stripping the outer sheath for about 30-50cm? The inner cores are still twisted, I needed to strip the sheath because the plaster is not thick enough for sheathed 8core cable. I have done the alarm cable.
For the 12v cable: I actually haven't done this yet. What is the issue with cable length between transformer and light? I have other cases (e.g. PoE and cctv) where 12v is run over a longer distance? I know I will get some voltage drop. I actually intend to test the configuration to ensure voltage drop is acceptable before installing.
Depends if the lighting trans are wire wound or electronic ones.
Sure, in general - but this is low voltage alarm cable, surely not a problem for a short run, it's sheathed to the top of the wall, but stripped back for 30-50cm out to a fire detector. It's not ideal, but under the circumstances (the alternative being to have some visible cable across a ceiling) it doesn't seem like a bad tradeoff. What negative consequences should I expect?
Unlikely, haven't done the calcs
- I doubt 22 to 24AWG could handle that load. I think PoE is <2amp anyway."Some"?
Before you get that far, just work it out.
You refer to "15A cable" - what's that? 1.5mm²?
32mV/A/m....
Sure, 1.24mm csa. Max cable length, 5m (probably a bit less). Calcs tell me drop is about 0.826. Do you agree? I checked some specs for G4 and AR111 bulbs, and looks like they tolerate +/- 2 volts or more. So should be fine.
While I think it's very poor workmanship, I agree on this one, it isn't likely to affect the performance of the cable in anyway way, nor cause you any significant problems.
Unlikely, haven't done the calcs
It's 15.4w max @ 48v for standard 802.3af compliant POE, so just over 0.3A, and that's spread across two pairs/four conductors.
"Some"?
Before you get that far, just work it out.
You refer to "15A cable" - what's that? 1.5mm²?
32mV/A/m....
Sure, 1.24mm csa. Max cable length, 5m (probably a bit less). Calcs tell me drop is about 0.826. Do you agree? I checked some specs for G4 and AR111 bulbs, and looks like they tolerate +/- 2 volts or more. So should be fine.
If BAS is correct with 32mV/A/m (I haven't checked but assume he is), then for your 150w loads you have 150w/12v = 12.5A. Multiply that by 5 metres to give 62.5, then by 0.032v, and you have a total drop of 2v on the ELV side of the transformer. That will be very noticeable, and based on fag-packet calculations, will take output at the light fitting down to about 100w instead of 150w.
It will be 2.31 volts if you use 1.25mm² cable (37mV/A/m).
Those lamps are going to be pretty dim.
Those lamps are going to be pretty dim.
And being halogens, have a short and blackened life....
For a 5 metre length and 12.5A, you will need at least 6mm cable and possibly bigger to get anywhere near an acceptable 3% volt drop.
No way that is going to be concealed in a 5mm thick layer of plaster.
No way that is going to be concealed in a 5mm thick layer of plaster.
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