Thanks to those who replied. The circuit work s fine but just occasionally = (too often for my boss) we get a failure. Maybe a transient but the questio= n is how. Oh well, keep digging... > I am having some trouble with a triac phase control circuit (attached) wh= ere I am getting a half wave conduction fault with the triacs.=20 Cheers Stephen --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .