Some circuits exist by rule, and some may carry nothing else
The exam tests the second part more than the first. Which circuits exist is the easy half. The restrictions on what else each one can feed are where the points are.
On this page
The required minimums
A dwelling has a set of branch circuits the code requires regardless of what the owner asked for: small appliance circuits, a laundry circuit, a bathroom circuit, and general lighting sized from floor area (NEC 210.11).
They are minimums. Nothing stops more being installed, and the exam sometimes offers a larger number as a distractor to see whether you know the difference between required and permitted.
The part that gets tested
Several of these circuits carry restrictions on what else they may supply. A small appliance circuit has no business feeding lighting. A bathroom circuit has rules about whether it may serve more than one bathroom.
Those restrictions are the exam material. Read each requirement together with its limitation, because the limitation is a separate sentence and it is the one people skip.
Where they meet the load calculation
The required circuits are not just an installation rule. They feed into the load calculation as fixed minimum values you add whether or not the question mentions them.
A candidate who calculates a dwelling load from floor area alone and forgets the small appliance and laundry minimums is short by a known amount every time.
That is why these two topics get studied together even though they sit in different articles.
Ratings and what may sit on a circuit
Branch circuit ratings are standardized, and the rating determines both what conductor is permitted and what may be connected.
A receptacle rating does not always match its circuit rating. There are conditions under which a lower rated receptacle may sit on a higher rated circuit, and that permission depends on how many receptacles are on it.
Read that section rather than reasoning from first principles, because the answer is counterintuitive in one direction.
What this page cites
- NEC 210.11 Required branch circuits in a dwelling.
- NEC 210.23 Permissible loads by branch circuit rating.
- NEC 120.52 The small appliance and laundry minimums as they enter the load calculation.