Electronic – Safety relay toggle time

Just to be sure we're on the same page, relay coils are between pins 1-12 and 6-7, not between 3-10. Also note that Q2 has some voltage drop even when turned on, so if you set the PSU to the latching voltage, the relay will see a smaller voltage and may not activate. Set the PSU to "rated" voltage, i.e. 5V. You could even leave it at 9V, since the relay is guaranteed to withstand up to 10.9V, though that's getting pretty close to the limit which is OK for a prototype but not advised for long-term usage.

If you put a 20mm to 40mm from MT1 to MT2 that protects your triac and driver IC. Another good target is the load itself, basically with the same protection.

MOV's have a soft low voltage clamp and a hard high voltage clamp. For 110VAC to 125 VAC you would use MOV's with a 150 volt rating stamped on them. I like them because they have no effect on power, just voltage spikes due to current surges due to switching off inductive loads. An MOV works best if placed at the point where the surge originates.

For 220VAC to 240VAC use MOV's marked 320 volts. For 277VAC use 420 volts MOV's. With a surge being clamped at the source, very little of it will make it to your Triac Driver.

Sidacs have a very tight clamp voltage but are very expensive.