Credit unit caps seem to be policies specific to the campus or division. For example (for students entering as frosh):
UCB L&S: https://ls.berkeley.edu/advising/planning/enrolling/unit-ceiling ; does not include college work done while in high school and only applies after 8 semesters
UCB CoE: http://engineering.berkeley.edu/academics/undergraduate-guide/degree-requirements-and-major-information ; 8 semester limit (regardless of credit units), must ask for permission for additional semesters
UCLA: http://cac.ucla.edu/academic-policies/unit-maximum/ ; appears lenient for those graduating within 4 years
UCSD: http://www.ucsd.edu/catalog/front/UgrdDegReq.html ; transfer units are counted only if they are applied to major or general education requirements
UCSB L&S: https://my.sa.ucsb.edu/catalog/2010-2011/CollegesDepartments/ls-intro/200UnitEnrollmentLimit.aspx ; does not include college work done while in high school and only applies after 12 quarters
UCI: http://senate.uci.edu/uci-academic-senate-manual/part-ii-regulations-of-the-irvine-division/chapter-i-section-3-scholarship-regulations/regulation-386-credit-hour-unit-limit-undergraduate/ ; “does not include units completed at another institution prior to matriculation”
UCD L&S: http://catalog.ucdavis.edu/ugraded/lsreqt.html ; only applies after 12 quarters
UCSC: http://senate.ucsc.edu/committees/cep-committee-on-educational-policy/policies-guidelines/undergraduate-education-policies/beyond12Qrters.pdf ; only applies after 12 quarters
UCR: 216 quarter unit limit; hard to find anything that lists exceptions
UCM: http://catalog.ucmerced.edu/content.php?catoid=2&navoid=60 ; 9 semester limit (credit units not mentioned), must ask for permission for additional semesters