ThemajordifferencebetweenthemeasuringCTsandProtectionCTsare:

(1)ThemeasuringCTsaremoreaccuratethantheprotectionCTs.ThemostcommoncompositeerrorlevelsofmeasuringCTsare0.5and1,whilethemostcommoncompositeerrorlevelsforprotectionCTsare5and10.

(2)ThesaturationlevelsofprotectionCTsaremuchhigherthantheCT'scurrentratings.ForprotectionCTs,itis10,15,20or30timeshigher,whileformeasuringCTitisatbest2times.

(3)ProtectionCTcanbeusedforthecoursemeasuringpurpose(notaccuratemeasurement),whilemeasuringCTshallnotbeusedforprotectionpurposebecauseoflowsaturationlevel.

(4)TheCTclass(IEC60044)forprotectionCTisdenotedby'P'(example5P20),whilethemeasuringCTisbyM(example1M)

Seethefollowinglinksforadditionalhelp:

http://cr4.globalspec.com/thread/43440

http://www.itluk.com/introductionprotectiontransformers.html

http://community.myelectrical.com/wikis/myelectricalwiki/ctdimensioning.aspx

http://cr4.globalspec.com/thread/51403