Does one need to be certified in order to do residential electrical work?
Home owners can do un &quot;certified&quot; electrical work on their own home in most states,. Unless you are the home owner, I'm quite sure you will find that in California, USA, just like most other states, you need to have a license to do electrical work for hire. Fixing minor things like replacing a light fixture or a broken switch does not fall into this category, however, adding circuits, doing anything in a panel, or upgrading services certainly does.
You would never be able to acquire any type of liability insurance as a contractor to do any kind of electrical work without a license, nor would you be able to pull a permit for a homeowner.
California has 5 different classifications of electrical license and each carries an apprenticeship: Voice/Data/Video Technician, Fire/Life/Safety Technician, Residential Electrician, General Electrician, and Electrical Contractor. Each one can take years to complete.
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I would caution you sternly, basic knowledge of codes and theory is not a substitute for practical knowledge/experience and  proper guidance from a seasoned professional.
Working in the trade as a unlicensed contractor could cause you a lot of grief and possible legal problems as well. I would suggest contacting your Secretary of State's  department or website for licensing requirements.