What Does Current Transformer 5P20 And 5P10 Mean?

Protection class versus metering class

AIRUIFA's published note groups current transformers as protection CT, special protection CT and measuring CT. The letter P marks a protection class. The number before P is the composite error limit in percent. The number after P is the accuracy limit factor — how many times rated current the CT must still meet that error.

What 5P20 means on a drawing

Class 5P20 means the composite error stays inside 5 percent up to 20 times rated current. Class 5P10 uses the same 5 percent error with a lower accuracy-limit factor of 10. Choose 5P20 when the protection relay must still see a faithful current during a heavy fault.

What to send with a 5P enquiry

Primary rating, burden, relay type and whether the housing must match an existing moulded or ring CT. AIRUIFA catalogues a PR 5P20 protection CT and checks production CTs on an OMICRON analyzer.