A light switch designed to switch 230 Volts AC may not be suitable for switching 12 Volts DC
AC voltage changes polarity 100 times a seconds and at each change there is a point in time where the voltage is zero.
When a switch is switched OFF an arc is formed as the contacts are separating.
A 3 mm gap between the open contacts will not ( normally ) allow an arc to persist. The arc will ( normally ) extinguish when the voltage wave form goes through zero volts.
With a DC supply the voltage does not go through zero volts and hence if an arc is formed then it may persist until the switch is damaged.
( normally ) = when the load being switched is not inductive. Motors and magnetic transformers are inductive loads
By "don't know about", I meant I don't know what their
DC specification is, if any. Discussions about modes of failure, contact materials, speed of switching, spark temperature or duration, protection diodes or suppressor capacitors etc might be technically interesting but this comment from a random forum (2018):
"I spoke at length with MK and they were adamant that their range of AC switches were not suitable for use on DC and could not give a derating factor."
tells me
no, you can't use ordinary mains light switches. Any consequential problem would see you as incompetent. An insurer would call it part of an electrical installation, which would evidence of conformity which you can't provide.
Caravan or boat switches may well be appropriately rated electrically, but may still not be approved for use in a house, I don't know.
It may be that by now one of the domestic accessory mfrs has got their switches approved for DC - please let me now if you find one.
One could use relays to switch the DC, with a tiny current to the light switch, but then the worms in the can surround the relay suitability, enclosure and whatnot.
The cabling is fine, for anything marked with a 230v rating it is generally "upto" 230v etc.
Ta.
I found some stuff - dumping the refs here...
https://electrical.theiet.org/wirin...echnical-considerations-for-dc-installations/
The wiring colour codes make mains cable OK for DC, part 10 of:
https://www.electricaltechnology.org/2020/07/electrical-wiring-color-codes-nec-iec.html
1sq mm is 18.1 mohms per metre, by the way. Could also be a problem.
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I have just found reference to SELV and FELV circuits. (Sub 60V)
SELV would not be suitable I think, because you need to connect 0V to Earth to reduce EMI.
FELV may be a suitable standard, but
"The SELV cables must be double insulated or pass through plastic conduits especially when they are likely to come into contact with other circuits."
probably applies to FELV as well, and wouldn't apply to existing mains wiring.