switching elv lighting.

thatbloke · 12 May 2010

i have in my house a number of old brass lights witches (all redundant) like this one

except they are not 'jelly mould' design. As i understand they cannot be used in any 230/240 volt circuit however i have often heard that they can be used in elv lighting situations. can a switch be fitted on the low voltage side of elv lighting?

edit - forgot to add , i know there are reproduction switches on the market but really they dont even come close to the original switches.

ban-all-sheds · 12 May 2010

thatbloke said:
i have in my house a number of old brass lights witches (all redundant) like this one

Funny looking switch.

except they are not 'jelly mould' design. As i understand they cannot be used in any 230/240 volt circuit however i have often heard that they can be used in elv lighting situations. can a switch be fitted on the low voltage side of elv lighting?

Almost certainly not - the current would probably be too high, and the voltage drop from all the extra cable would be ruinous.

thatbloke · 12 May 2010

the current would be too high? if the elv lighting ran from a single transformer (or am i dreaming that this exists?) then the feed from the transformer to the lights wouldn't be enough to cause any damage to the switch would it? sorry if these are silly questions but i have heard from several different sources that these switches do not meet building regs but can be used in low voltage situations , a quick google for a pic even brought up this.

http://www.antiquedoorfittings.co.u...Ceramic-quotJelly-Mouldquot-Light-Switch.html

flameport · 12 May 2010

ELV lighting uses far more current than LV.
A single 50W, 12V lamp would be over 4 amps.
6 of them on a single switch (not exactly unlilkey) would mean 25 amps going through the switch and cable (which would have to be at least 4mm, and probably much larger).

If you want to use these old switches, one option is to use relays. The switch operates at 12V ac, and switches power to the relay coil only.
The relay contacts switch the usual 230V, and therefore you can have any lighting you want.
Normally this would be set up with a central relay cabinet, and you will need to completely rewire the lighting circuits. The cost of all this will be significant.

securespark · 12 May 2010

The current drawn by a 50W lamp at 12V is around 4.2 A.

But, more than that, if you are switching the SELV output, you need large CSA conductors so as not to drop too much voltage. The longer this cable, the larger the CSA of these conductors needs to be.

EDIT: Sorry FP, our posts crossed in the ether...

mikeyd · 12 May 2010

One way you could use those switches without worrying about putting either more Volts across it, or more current through it than it was designed for is to use it to switch a control signal to a relay or some kind of home automation system.

Forget about using it to switch ELV (12V) lighting. One single 60 Watt bulb takes about 5 Amps on a 12 Volt circuit.

And don't use them to switch LV (240V) either. If it's old it might not be as well insulated as it once was so when you or yours go near it with damp hands....

EDIT: in other words, what they said above.

thatbloke · 12 May 2010

the relay sounds like a good idea , i have used relays in automotive applications before but never in this kind of environment.
i would need a 12 volt supply to switch the relay so a 12 volt transformer would be required , this could then switch a 230 volt relay to switch the elv lighting supply , or is it a bit more complicated than that?

edit - sorry , i am assuming the relay is switched with a 12 volt signal.

ban-all-sheds · 12 May 2010

thatbloke said:
http://www.antiquedoorfittings.co.uk/ourshop/prod_112000-VictorianEdwardian-Brass-amp-Ceramic-quotJelly-Mouldquot-Light-Switch.html

"it is important
to check current regulations if you intend to use it on a live
240V circuit,although ideal on low voltage systems."

Those people should not be in business

1) As observed, using switches like that for ELV will probably destroy them.

2) As observed, extensive cabling for ELV lighting will either be impossibly large or will have crippling voltage drop issues.

3) 240V IS low voltage...

thatbloke · 12 May 2010

ban-all-sheds said:
3) 240V IS low voltage...

ah , i was getting confused there.
a central relay cabinet sounds complicated , would this be like a second CU except housing relays?

mikeyd · 12 May 2010

thatbloke said:
the relay sounds like a good idea , i have used relays in automotive applications before but never in this kind of environment.
i would need a 12 volt supply to switch the relay so a 12 volt transformer would be required , this could then switch a 230 volt relay to switch the elv lighting supply , or is it a bit more complicated than that?

edit - sorry , i am assuming the relay is switched with a 12 volt signal.

You don't want to go down the route of switching 230 volt with a relay.

If you really want to use those switches then in my opinion the sensible way would be to use them in conjunction with a home automation system such as X10 (Others are available)

ban-all-sheds · 12 May 2010

And they are all better.

But....

thatbloke said:
a central relay cabinet sounds complicated , would this be like a second CU except housing relays?

probably not for him.

thatbloke · 12 May 2010

i am not up on my home automation systems but dont they use digital pulses sent through existing wiring to a receiver that your appliance plugs into? how can i send a signal to a receiver through one of these switches?

ban-all-sheds · 12 May 2010

thatbloke said:
ban-all-sheds said:

3) 240V IS low voltage...

Click to expand...

ah , i was getting confused there.

Not you - it's those people who falsely think they are competent to be in the electrical accessory business who are confused.

a central relay cabinet sounds complicated , would this be like a second CU except housing relays?

Just fit some proper, safe, modern light switches.

thatbloke · 12 May 2010

ban-all-sheds said:
And they are all better.

But....

thatbloke said:

a central relay cabinet sounds complicated , would this be like a second CU except housing relays?

Click to expand...

probably not for him.

your probably right.

thatbloke · 13 May 2010

ban-all-sheds said:
Just fit some proper, safe, modern light switches.

i am beginning to think you are right , all this is beginning to sound very complicated and very expensive.
i believe that one of the problems with these old light switches is that the screw off covers are not allowed , if i were to change the cover from a new switch with the cover from an old one and fit a grub screw then this should be ok?
its the covers on the new switches that i cant live with , the lacquered brass 'effect' would just look cheap and nasty in the environment these switches are to be used in (or were to be used in before i found out how complicated all this is becoming). [/b]

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switching elv lighting.

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