PS class means protectionclass CT. 5P10 means 5% errorshown while 10 times fault current flows.and 5P20 5% errorshown while 20 times fault current flowshence 5P20 superior comparing to 5P10
Two types of CTs. one is for metering another one is for ProtectionThe metering CT has very less error,the protection CT has more error but thathas more saturation level.5 - 5% error. P for protection and 10 indicates 10 times the rated current.
it means accuracy class of CT. 5 p means 5 % of composite error will happen till 20 times of current is applied . So CT will follow its rated characterstics upto 20 times currentRead more: What_does_mean_by_5p20_CT