Switching 12V transformer

[frediaz]

Is it possible to install a switch for a 230-12V transformer, serving a single spot light, on a wire going from the transformer to the light or does it have to be on the mains (live) wire to the transformer?
If it is possible, is it necessary to install an FCU on the mains cable to the transformer?

Ta

 

[breezer]

you could put the switch on the 12v side, but you dont because

1) the transformer is still on

2) For one lamp its not too bad, but but 2 or more and the current will be around 8 + Amps (depending on how many and what watt of lamps) a normal light switch can only switch 5 Amps

3) Voltage drop


By switching the mains you dont have any of the above poblems

 

[TicklyT]

Another problem is some electronic 'transformers' shut down if their output is open circuit, as it will with a switch in the output. Then they stay shut down until the mains supply is switched off, then on again. That's 'a little bit inconvenient' if you can only turn it off at the CU.

There's probably little need for a FCU if the transformer is connected to a lighting circuit protected by a 5 Amp fuse / 6 Amp breaker.

An FCU would be required if the transformer is connected to a socket circuit.

You could consider using a switched fused connection unit to combine both functions.

 

[frediaz]

Thanks for the advice, I am going to switch it on the 230V side to avoid potential problems. I am told 12V transformers can be troublesome

 

[ericmark]

With a transformer yes but an inverter will often have a min as well as max load so not with inverter.

Also there is a problem with cables sizes for example a 50W spot light at 12 volt uses 4.2A and you are allowed a 3% volt drop that's 0.36V so max cable resistance = 0.36/4.2 = 0.08 ohms so 2.5mm cable at 0.018 ohms per meter has max length of 4.8 meters. With 4mm it is 7.8 meters and bigger than 4mm you will have a problem in terminating.

Move to using a couple of 50W lamps then really becomes a problem.

Transformers are a lot heavier than inverters. Don't trust the name transformer it is loosely used to refer to inverters as well as transformers in the same way as many call extra low voltage "Low Voltage" when "Low Voltage AC" = 50 - 1000V.