What is the chance of contracting hiv/aids when having protected sex with an infected person? is there 0 chance, or no chance at all if used properly?

0 chance means...: There is likely 0 chance, mathematically rounding to 0, of course. The only things certain in life are "death and taxes", although I've been recently reminded that some people avoid taxes by hiring a clever tax lawyer. In any case, there are no exact chance numbers for catching HIV, so one must live every day wisely. Avoid infected people, if one tends to worry. Life is never exact.