transformerwiring
I have a 220 V to 110 V transformer but it's not the type which comes with the plug and outlet built-in so I need to make the connections myself.
The only problem I have is that I'm not sure which terminal is live and which is neutral. I don't see any signs indicating which is which. So does it matter?
Pictures should help:
As @Asmyldof stated, the motor has no concept of hot or neutral, so the polarity of the AC connections is not important. Connect one of them to hot, and one of them to neutral. The motor will turn the same direction even if you reverse these connections. To reverse the motor, you have to remove the metal jumpers, and reposition them as indicated by the diagram.
Note that you absolutely should ground the motor housing, but this is a protective measure (the yellow/green-stripe wire is the earth/ground connection), but ground is not neutral.
The four outputs on the inlet are numbered 2-4-3-1 from the top down in the diagram.
Your link to the diagram is broken, I will assume it's the same as the diagram in http://www.farnell.com/datasheets/1511815.pdf
I think that wires 1 and 4 should run to the two closed terminals on the switch, and the common terminals on the switch should run to matching wires on the transformer. Wires 2 and 3 should go directly to the transformer.
What you propose will work but your double pole switch will effectively only provide single pole switching. If you wanted full double pole switching you would need a four pole switch.
That is probablly not a problem for a functional switch on a transformer powered device but it's something to be aware of.
PS: I know that the inlet has a built-in switch. I want a separate switch because it has a nice LED on-off display and will be on the front panel of the device, rather than its back.
You might want to think about how the indicator light (it's probablly a neon not an LED) will end up connected in both 120V and 240V modes
PPS: When connecting mains wires to the primary windings, does polarity matter?
It matters that the two windings are connected with the same polarity. Otherwise they will "fight" each other resulting in an effective short circuit.
Best Answer
You should be able to determine which terminals are neutral (or rather common between input and output) by measuring resistance between each of the 220V terminals and each of the 110V terminals. All resistances will probably be very low, but the lowest resistance combination should be the common terminals,and you would use those as Neutral.