how to format time as hours minutes and seconds

Dear Forum Team

I am trying to format cells so they are able to accept hours, minutes, seconds. Numbers doesn't appear to be able to do this without attaching a date to the hour, minutes,seconds which it then assumes is time. I would like to be able to add up a column of numbers that would give and hour,minute,second answer ; eg 35:24:33 + 12:15:33 = 47:40:06

Any Suggestions?