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Topic Title: Bathroom light switches
Topic Summary: Are relays on a SELV supply a solution?
Created On: 11 August 2017 04:14 PM
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 11 August 2017 04:14 PM
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Dreckly

Posts: 41
Joined: 03 December 2014

Hello

My customer would like to have his bathroom lighting in three groups and there is an extractor fan too. He doesn't want 4 pull switches! The logical place for a plate switch will be in Zone 2. He would much prefer a normal plate switch to product such as Taptile.

I'm thinking of putting 4 relays to switch the lights and fan in an enclosure in the loft space. Power for the relays would come from a 12v DC SELV supply, also in the loft space. The 4 gang plate switch would be a standard 230v switch to match the other accessories. Although not designed for DC, the current will be a fraction of an amp.

It seems a neat solution to an age old problem which makes me thing that if it was that easy someone else would have tried it before!
Am I missing something here?

Regards

Dave
 11 August 2017 04:42 PM
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scottseedell

Posts: 90
Joined: 05 June 2009

I'm not sure why you would want relays. So you want to use the grid switches to switch independent relays that control the lights/fan? Surely that's just adding unnecessary parts to the installation. Why not just put the Tx in the loft in a decent sized enclosure, put some terminals in there for neatness, use this as a marshalling box and then run 4x independent low voltage switch drops down to the switches?

-------------------------
Scott Seedell - MSc IEng MIET
 11 August 2017 04:43 PM
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scottseedell

Posts: 90
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Ah I see, the fan and lights are 230V I take it?

-------------------------
Scott Seedell - MSc IEng MIET
 11 August 2017 04:52 PM
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Dreckly

Posts: 41
Joined: 03 December 2014

Yes, that's it Scott. Making the whole installation within the bathroom SELV would require a much larger and expensive power supply.

Regards

Dave
 11 August 2017 05:01 PM
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scottseedell

Posts: 90
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On the face of it then, it seems like a reasonable way to remotely switch 230V. May be a nightmare for the next bloke that comes along deciphering all of that though...I worked with a domestic spark once that had never seen a relay once in his 30yr career.

Even easier though, surely if the bathroom is large enough to have 3 separate lighting circuit then there is sufficient room to mount any switches out of zone 2?

-------------------------
Scott Seedell - MSc IEng MIET
 11 August 2017 05:22 PM
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Dreckly

Posts: 41
Joined: 03 December 2014

The three groups of lights are more to do with mood lighting than total illumination. Just inside the door is the wall of the shower enclosure. That's only logical and convenient place for a switch.

Regards

Dave
 11 August 2017 07:02 PM
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mapj1

Posts: 9107
Joined: 22 July 2004

No problem, and a contactor version of the same sort of thing is quite common in commercial settings.
If you like it to fit together neatly then relays that plug into a DIN rail are available.
You could browse the TLC catalogue.
I'd look near here for inspiration.

any 12V DC supply designed for SELV use such as telephones will do
There is the largely academic concern that EN 60950 to which many DC supplies claim conformance is not directly called up in BS7671 as 'acceptable' however, it only says BS 61558-2-6 for traditional transformers, and DC power supplies to 'equivalent' safety standards, presumably of insulation, breakdown and EMC generation, are fine .

Or earth one side of the DC output and call it PELV instead...

If you are worried about the next man in, then print a copy of the circuit and leave it in the relay box, and a note behind the switch plates.


Be aware you may need RC suppression across the contacts of the relays or the load side if contact flash or EMI like clicking on the radio or false trigger of PIRs on same circuit etc is a problem.

-------------------------
regards Mike


Edited: 11 August 2017 at 07:21 PM by mapj1
 11 August 2017 07:54 PM
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geoffsd

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Originally posted by: Dreckly
Just inside the door is the wall of the shower enclosure.


Don't forget - the zones are determined by measuring around shower enclosures; not through them.
 11 August 2017 08:59 PM
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monk

Posts: 67
Joined: 08 December 2012

All that seems like a lot of faff
Why not try something wireless?
https://www.tlc-direct.co.uk/Main_Index/Wiring_Accessories_Menu_Index/Quinetic/index.html
 11 August 2017 10:58 PM
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AJJewsbury

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It seems a neat solution to an age old problem which makes me thing that if it was that easy someone else would have tried it before!

I've heard of it being done in historical buildings where they wanted to keep the original switches but they weren't safe enough for continued use at mains voltage. A some modern building management systems I think amount to the same thing too (if with a small computer between the switch and relay).

Do try and make sure that's there's sufficient isolation between the relay coils and contacts though - you wouldn't want the ELV side creeping up to mains voltage just because a bit of arcing and carbon deposits allowed tracking between the two sides.

There is the largely academic concern that EN 60950 to which many DC supplies claim conformance is not directly called up in BS7671 as 'acceptable' however, it only says BS 61558-2-6 for traditional transformers

Or just use a conventional door bell transformer (which is to BS EN 61558-2-8, which is listed now too )

- Andy.
 11 August 2017 11:51 PM
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MWalker86

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 12 August 2017 12:42 AM
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geoffsd

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The link doesn't work.

I have seen one of Mr.Ward's videos where he just states the regulations regarding bathroom switches.
 12 August 2017 12:53 AM
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mapj1

Posts: 9107
Joined: 22 July 2004

the link is missing a colon after the https.
So
try here

However, I think he needs to clean his pull cord - and I'd go the other way and put pull switches in some non bathrooms too.
(like above the bed.. ) I have also used them as a nice way of getting a switch actualtor into an other place, both outside through a wall for outside lights, and also out of a screened roome where no wiring was allowed, but we wanted an alarm.
edited as my link did not work either...

-------------------------
regards Mike


Edited: 12 August 2017 at 01:43 AM by mapj1
 12 August 2017 12:53 AM
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MWalker86

Posts: 81
Joined: 05 June 2017

Hmmm, I can see how the url is not right but it seems to not actually edit it when I edit it, even though it says it has.

Try this
 12 August 2017 12:56 AM
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MWalker86

Posts: 81
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Whilst I agree with the sentiment I would definitely disagree with his measured definition of 'out of reach'. I'm damn sure I could reach further than 60cm from the centre of my body and I'm not inspector gadget.
 12 August 2017 02:07 AM
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mapj1

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Well I think the original 3m was 'out of reach', of all but Mr Tickle, and is a distance retained for sockets, as being out of reach plus the length of the lead on a hairdryer or similar.
cord switches first appear on page 87 of the 12th edition, and cupboards are mentioned as equivalent, so in1950 or so you could have a normal round pin 5 A socket in a bathroom cabinet above the sink and meet the regs of the day. Later editions explicitaly banned sockets from any room with a fixed bath or shower, a situation that continued for about half a century when they snuck back in, as it were.
Oddly in the same way as we are pushed to harmonise and permit bathroom sockets like in the EU, and the old folk chunter, I have spoken to some older Germnan sparks bemoaning the )substitution of 30mA for 10mA for RCD protection for bathrooms, and how it was better when they used to put the light switches outside the bathroom, often with an indicator lamp, so you knew if the light was on with the door closed. As this is mentioned in the same breath as red cable for earths, I suspect the change is going back quite a long way into the 1970s perhaps. (maybe even when I was still in short trousers and had a leather school satchel...)
Equally in the UK the 30mA figure has a similar fairly short pedigree being 1981 for the first appearance as a regs requirement
Ah there is clearly more than one right answer.

-------------------------
regards Mike


Edited: 12 August 2017 at 02:14 AM by mapj1
 12 August 2017 02:17 AM
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MWalker86

Posts: 81
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You know 12th edition regs?!
 12 August 2017 07:53 AM
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Dreckly

Posts: 41
Joined: 03 December 2014

Thanks for all the late night posts.
The wireless switch option is certainly worth considering.
The products that I was thinking of using were these DIN rail relays http://uk.rs-online.com/web/p/...tching-relays/7943780/ and this power supply https://www.rapidonline.com/powerled-pcv1220-constant-voltage-led-power-supply-12v-0-1-7a-20w-85-3906, which is marked SELV.
I hope those links work. Now how did you folks insert the links above?

Regards

Dave
 12 August 2017 09:02 AM
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tomgunn

Posts: 3864
Joined: 25 May 2005

Sadly... even though we're allowed to do so... I would never put a switch in a bathroom... I'm always a worrier!

-------------------------
Tom.... (The TERMINATOR).

handyTRADESMAN ... haha

Castle Builders
 12 August 2017 09:07 AM
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dustydazzler

Posts: 1177
Joined: 19 January 2016

It's funny , my parents holiday apartment in Crete has a normal light switch in the bathroom and a normal 2 pin socket right next to the sink and we don't bat an eyelid using either after hopping out the shower.
But if we put a light switch and socket by the bathroom sink here in the uk we would be encroaching on badger status
IET » Wiring and the regulations » Bathroom light switches

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