Sensor cable for bathroom lighting

[tackit]

I need to get the wires for the low voltage dimmer sensor pads in place while I'm tiling the bathroom.

I've read the documents available from the website I'm buying the sensors from and it refers to 'low voltage' cable.

Is 1mm T@E OK for the job?

http://www.sensor.co.uk

http://www.sensor.co.uk/resources/S...nstructions/Bathroom_Dimmer-_Instructions.pdf

Also is a 'double pole isolation switch' required and if so why?

 

[flameport]

The instructions are poor, with various mixed and incorrect terminology, and they don't actually specify what type of wire/cable is suitable.

However as the sensors use 5V it's likely that almost any wire would be suitable, T&E included. The only issue is the size of the terminals on the devices - T&E may be too large to fit, particularly with more than one sensor.

 

[tackit]

Just found this on the site:

"To connect the Sensor Pad to the Controller, use speaker cable or bell wire, if your cable run is likely to pass close to
another Sensor Pad’s cable or mains voltage cable, or you have a long run of cable, we recommend using “CAT 5” cable.
If you are using existing “twin & earth”, connect the earth wire to a convenient earth connection at the controller end,
leaving the sensor end un-connected."

What about the 'double pole isolation switch", is that required?

 

[bernardgreen]

However as the sensors use 5V it's likely that almost any wire would be suitable, T&E included.

The 5 volt is derived in some way from the 230 mains. Without knowing what level of isolation exists between the 5 volt and the 230 volt it would be sensible to treat the 5 volt wiring as a potential hazardous should a fault develop in the controller.

It would also be sensible to use 230 twin and earth to allow for easy ( easier )replacement of the touch switch with a normal switch should the touch switch fail or otherwise become unwanted.

 

[ericmark]

As said instructions are poor we use IET/BSi regulations here but instructions refer to IEC which is the international version and there are variations country to country.

In this country where we use TN supplies we don't need to switch the neutral to isolate but in some countries the neutral can float in respect to earth much more then here and I would assume the double pole switch is stipulated to allow for when used in countries where the neutral and earth float more than here.

However with any device be it a fan or a light dimmer it can fail and having a means to isolate is always good so if it goes faulty you don't lose lights else where in the house.

Personally I would swap the standard light switch for a keyed switch like this

so it will not be normally used but can in an emergency be used to isolate. Since my house is TN-C-S I would not worry about being single pole. However it's down to person fitting it and if they say they want twin pole then twin pole it is.

Again although I like the idea of touch pads I do not like the idea of dimmers when I walk into a room I want light not having to wait for lights to reach full brilliance. I would also hope there is provision to connect earth wires.

It would seem the instructions are written by a non electrician as there are some errors for example 5 VDC is extra low voltage not low voltage may be designed for USA market?

 

[AndyPRK]

I'm not sure a key switch is a good idea for a house.
If it was ever required to be used one would have to remember its a key switch and then have to find the key!!!

 

[ericmark]

bernardgreen makes a good point

Isolation sign

• ericmark
• 12 Mar 2009
• 10

should appear if the transformer is rated for isolation unless that is shown then all wires need to be 230 volt rated.

I see the point raised about lost key so may be fused connection unit better idea can remove fuse if goes faulty.

I have looked at a few remote lamp controllers but rejected them because they need tungsten lighting to work. I would not fit any unit today which will not work with LED lights. I do note there is a version which does not include dimming but comments that over 500W will cause the unit to fail permanently makes me think it's an electronic switch not a relay the electronic switch is well know for allowing a small current through even when switched off so likely it will not work with either CFL or LED as such it's an out dated unit and I would personally not fit I would want something which I can continue to use in the future.

 

[bernardgreen]

Isolation sign

• ericmark
• 12 Mar 2009
• 10

should appear if the transformer is rated for isolation

Not all have transformer isolation. There are "ELV" supplies where the 0 volt is connected to Neutral and Live 230 volts is dropped to 5 or 12 by a series resistor + capacitor and Zener diode. Absolutely NO isolation in these items.

This is OK in items like PIR sensors built into lamps where the ELV circuit is completely contained within the item's casing.

It is totally un-acceptable when the ELV does come out side the casing for any reason and is extremely hazardous if the Live and Neutral supply are reversed.

 

[tackit]

Well thanks for the replies, although some of it's over my head.

I have just cut 4 holes in my bathroom ceiling, so 200w max.

I need to install wires soon, do I go with 1mm T&E or some bell/speaker wires? I'm currently thinking on the latter as it's cheaper and what they recommend.

Many thanks indeed.

Also the T&E would never be any good for a general light switch as it's in a bathroom.