As the other respondents mentioned - the hot and neutral are just terms. With 3 phase whilst you have two phases 120 degrees apart, what you see between the phases is a sine wave- otherwise transformers would have a hard time working! Also if your 3 phase is 110v from phase to neutral, then you will have about 200v between phases.

Note that your circuit has no snubbers - fine if you are only switching resistive loads. Also the snubbers protect the devices against high voltage spikes. I would suggest you review the datasheets for the opto and triac for information regarding this. I learnt the hard way!


I've never come across a 4N40 before!