Triac going short circuit

[engineer1000]

I used a triac circuit design form littlefuse AN1003.16 Phase control permanent magnet motor. I connected it up to 115v ac and measured the outut on a multimeter. I measure approx 100v before the triac when short circuit and blow a trip.
Not sure what I have done wrong, does it matter which way MT1 and MT2 are connected? is the circuit correct?

 

[thylacine1975]

The application note circuit looks OK - what device are you using? Is it appropriately sized (i.e. current rating) for the motor you're driving? Motors can be tricky beasts to determine appropriate component ratings - if possible, go for a healthy (factor of 5x?) safety margin between your anticipated stall current and TRIAC rating.

The polarity of MT1 and MT2 often *does* matter for alternistor TRIACs - they don't trigger reliably in all quadrants. Check the datasheet for the device you're using and make sure your trigger current looks OK for the polarity of gate and MT2 (with respect to MT1) voltages you expect.
(...or just swap them over and see if it works