@Gyro: you are right, the fuse is rated at 750mA, so having 4-5 solenoid running at the same time is likely to trigger it. The triacs are rated at 800mA continuous current and 8A impulse current. To be honest, when I designed the circuit, I didn’t realize that the PTC fuse is a slow-action type. So by the time it triggers, the triac may already be destroyed (say, if a solenoid is defective and short circuited). Therefore the PTC fuse may not be very useful.