Hi!

I have a Leviton 057 dimmer switch with two black wires and one that is green.
The box in my apartment has two wires--both black, but one is much thicker than the other.
I don't have the means of testing to see which is live. Can anyone please tell me which wires go where?

Thanks for your help!

If a switch was there, you should be able to connect 2 switch wires to box wires.
#12 should be protected by 20 Amp Breaker.
#14 should be protected by 15 Amp Breaker.
Smaller than that should be replaced.