I bought this small cheap transformer for my nest hello smart bell, it has 3 input options "4 wires" if i use 220v input wires it gives me 30 volt output without load of course. If i use the 440 input wires it gives me 15 volt output, also without load. My question is: Is it safe to use the 440 input wires with my 230v outlet socket?
3:
You could power it between the 440V and 110V wires and get 18VAC under full load and probably about 20VAC open, which is well within the 16-24VAC operating range of the bell. The VA is adequate.
It's claimed to be a Class 2 transformer (though notably bereft of any visible markings and file numbers indicating that it has been tested to meet that requirement) so it should (they say) fail safely, however having such things in a grounded metal enclosure or otherwise mounted to something non-flammable is never a bad idea IMHO.
Is it safe to use the 440 input wires with my 230v outlet socket?
It won't damage the transformer and should provide you with about half the VA rated output stated on the label. Given that it is a 40 VA transformer you can expect to use this for a 20 VA load.
However, your load requires a 16 volt AC output and, running at 440 volt AC, the transformer only produces 15 volt AC so there is a shortfall. It may work or it may not but, it should be safe.
If you test it and it all looks fine, keep an eye on it for a couple of hours just to be sure.
