On most building jobs the general contractor is the prime. Some public owners sign several primes, such as general, mechanical, electrical and plumbing.
The bid documents tell you which case applies. On a multiple prime job, an electrical contractor bids to the owner and carries its own bonds.
Check who you sign with before you price. A prime carries more duties from the front end documents. Those duties can include bonds, insurance, schedules and closeout.
If you bid as a sub, ask the prime which of those duties flow down to you.