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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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 12 August 2017 11:44 AM
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Posts: 2578
Joined: 07 August 2007

To return to the original question, I agree that ELV switches operating relays is a sensible approach.
The only slight objection that I can see, is that failure of the transformer or PSU from which the ELV is derived would extinguish all the lights.
For this reason I might favour an old fashioned wound transformer rather than SMPS.

Alternatively, wire one of the relays and controlling ELV switch such that the relay coil is energised to turn the light OFF. That way any failure of the ELV supply would turn one of the lighting circuits on, and leave it on until the ELV supply was replaced.

I have done this in an historic house where it was desired to retain original brass light switches and the old VIR cables thereto.
12 volt SMPU in loft, and relays.
 12 August 2017 05:54 PM
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It will be no trouble to wire one of the relays as you suggest.
I have a feeling my customer will choose to have a metal plate switch now, just because he can


 12 August 2017 05:55 PM
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You know 12th edition regs?!

well not in the sense of ever having been there at the time, I'm not that old...
But I do have access to copies of some old stuff, and from time to time one comes accross an installation from days past, and it is interesting (and occasionally useful) to know what the regs would have expected at the time.
And I am lucky enough to have the sort of memory that allows me to absorb stuff and be very careless about where I put it down, and have the key data from several hundred transitors, ICs and other things on tap. Drives the wife mad - as she is the opposite, and can watch the same film again after a year as she has forgotton how it ends. Equally, names and what I had for breakfast, are lost immedately with no chance of recall.

regards Mike
 12 August 2017 09:42 PM
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Mike I can recommend Groundhog Day to your wife!
IET » Wiring and the regulations » Bathroom light switches

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