Current Transformer Parameters
RLC-50 is the series number. You can use that to look up the datasheet, especially if you know the manufacturer name, since more than one maker uses that series name (probably copied from ABB). The 50 refers to the inside diameter of the hole in the CT (~50mm). 

PT is primary turns for the rated 400:5 ratio. One turn means that you just run the high-current wire through the hole and don't loop it more than once.