Ob txoj kev sib cais tau ua raws li thoob ntiaj teb kev loj hlob ntawm cov kev cai hluav taws xob thiab cov qauv rau cov chaw muaj kev phom sij.
Tau ntau xyoo lawm, ib qho "Class, Division" System tau ua lub hauv paus rau thaj chaw categorization ntawm kev phom sij (qhib) qhov chaw hauv North America.
Xav txog cov kev pheej hmoo thiab cov tswv yim tiv thaiv
ntau yam khoom siv yuav tsum muaj ntau yam khoom siv hluav taws xob los tiv thaiv cov kev pheej hmoo no, thiab cov chaw muaj kev puas tsuaj tau tawg ua peb chav kawm thiab ob chav.
Cov cheeb tsam uas muaj peev xwm tawg tau zoo yog siv los ntawm "Zone System" hauv ntau thaj tsam ntawm lub ntiaj teb. Lub International Electrotechnical Commission (IEC) thiab European Committee rau Electrotechnical Standardization (CENELEC) yog cov qauv tseem ceeb ntawm cov cheeb tsam twg.
Qhov "Class, Division" System thiab "Zone" System tau sib piv hauv cov lus hauv qab no.
Tus nqi txaus ntshai nyob rau hauv ib qhov chaw yog txiav txim los ntawm qhov zaus ntawm qhov tshwm sim; ntev ib yam khoom nyob ntawd, qhov kev pheej hmoo ntau dua.
Qhov sib txawv ntawm ob peb Zones tau piav qhia hauv kab ntawv hauv qab no.
Nyob rau hauv cov nqe lus ntawm kev soj ntsuam kev pheej hmoo, daim duab hauv qab no sib piv cov Division thiab Zone systems.
