Smoke alarms

[Master of None]

I have purchased one of each of these for my bungalow.
http://www.screwfix.com/p/dicon-ionisation-alarm-with-9v-battery-backup/81969
http://www.screwfix.com/p/dicon-photoelectric-alarm-with-9v-battery-backup/84956
Upon reading the instructions it says "Do not install within 1500mm of a fluorescent light fitting and keep wiring at least 1000mm from these fittings. Do not install alarms on circuits containing fluorescent light fittings or dimmer switches."
Do energy saving lamps fall into this catogory?
Also in the box for the photoelectric one there is small ferrite tube about 25mm long with 2 cable ties. There is no reference to this in the instructions. Does this need to be slipped over the wire at the alarm?
Thank you.

 

[Master of None]

Anyone.
Its just there is only a postage address for technical support and I thought one of you guys would have came across this before.
Thankyou.

 

[Alarm]

You should be okay with the lights.
The ferrite tube is to throw off RFI . Feed the cable through it and then along the length and back through, use the cable ties to hold it in place.

 

[TheGayOwl]

Lots of energy saving lamps are indeed fluorescent, commonly called compact fluorescent lamps (CFLs). LED's are becoming more common. You should check what you already have installed regarding floros and dimmers.

The small iron tube is a mystery to me. I would say if it does not mention it in instructions then do not worry about it.

I have never had to put any tubes on mains powered smokes ever.

Regards.

 

[Alarm]

They are fine with the CFL litttle energy savers.
The ferrite tube is to stop any throw backs of RFI. Radio Interference.
Just keep them off dimmers.

 

[TheGayOwl]

Alarm, would a 'proper' floro with a 'proper' ballast/choke cause probs do you known at all?

Ta

 

[Alarm]

From what I understand the back EMF would cause an issue. Hence the ferrite tube again. They give it out as they know people will fit them to circuits with tubes/dimmers.

It costs you money, silly to not use it.

 

[Space cat]

The circuit for a 'proper' fluorescent lamp is:

Live -> choke -> first tube filament -> starter -> second tube filament -> neutral and, before the arrival of electronic starters, it worked like this.

1) The tube is non-conducting so full mains voltage appears at the starter.

2) This ignites a gas discharge inside the starter and current flows, limited by the choke.

3) The tube filaments heat up. You can see this happening but, out of sight inside the starter, a bi-metal switch is also getting hot.

4) The bi-metal switch pops open, breaking the circuit.

5) The choke, being an inductor, generates whatever voltage it takes to keep the current flowing.

6) With hot filaments and a high voltage spike across it, the tube strikes.

7) The bi-metal switch cools and closes again but, with the tube now conducting, the voltage across the starter is too low to initiate a gas discharge. It's job is done

But tubes don't always strike first time. They can flicker many times and each flicker is a high voltage spike putting out a lot of electrical noise. There's a capacitor across the incoming supply to limit this noise but some will escape.

I've never opened up a compact fluorescent lamp (must get round to it some day) but it's clear from their weight that the modern ones don't have a regular choke in there. My understanding is that they convert the mains voltage to a high frequency that can ignite the tube directly and so their noise output is much lower.

Dimmer switches are also potentially noisy but for a different reason. They work by cutting out the first part of each half cycle of the mains voltage. When you turn one right down, the waveform going to the load is a string of very narrow spikes, full of high frequency components. The ones I've used all had a small inductor in there to smooth out the current a bit. (If you ever here a dimmer buzzing, that's magnetostriction in the inductor's core.)

For what it's worth, we have a set of three interlinked, mains-powered smoke alarms in our stairwell. They take their power from a lighting circuit with three CFLs on it and two filament bulbs on a dimmer switch. None of these has ever caused a false alarm.

 

[Master of None]

I have CFL's on both circuits but no dimmers so should be ok.
Thanks for all the help guys.