Interviewers sometimes ask about what might seem like very basic knowledge to weed out people who lack the foundational knowledge necessary to succeed in the job. Be prepared to explain key concepts relevant to the work of an electrician to demonstrate that you have an understanding of the work and what it involves. If you happen to get asked a question that you don't know the answer to, you still might be fine if you can explain to the interviewer how you would approach finding the answer if faced with a need to know the information in the field.