Yes, you've got the general idea correct! Here's a more detailed breakdown to solidify your understanding

Part 2 Calculations (Branch Circuits): "How much load can I put on this specific circuit?"
You're absolutely right. Part 2 focuses on individual branch circuits. The goal is to determine the maximum allowable load (in amps, watts, or VA) you can safely connect to a specific branch circuit based on its: Ampacity of the Conductors

What is the rating of the wire?

Overcurrent Protection Device

What is the rating of the breaker or fuse?

Type of Load

Is it a continuous load, a non-continuous load, a motor, or a combination?

Specific Requirements for Specific Equipment

Ranges, dryers, etc. have their own calculations.

Key Question

Given this circuit (breaker size, wire gauge, outlet type), how many lights, receptacles, appliances, etc. can I safely connect without overloading it?



Think of it this way

You start with a defined circuit (e.g., a 20A circuit with 12 AWG wire) and determine the maximum load you can attach. This ensures that individual branch circuits are not overloaded.

Part 3 & 4 Calculations (Feeders, Services, and Panelboards): "How big do I need to make this system to handle all the load?" You are correct. These sections are about sizing the entire electrical system (or large portions of it).

Part 3 (Feeders)

Feeders are the conductors between the service equipment (like the main panel) and a subpanel or a specific load center. Part 3 helps you determine the minimum ampacity required for the feeder conductors based on the total calculated load they will serve.

Part 4 (Service)

The service is the entire electrical supply to a building. Part 4 calculates the minimum size (ampacity) of the service conductors, the service equipment (main breaker, disconnect), and the grounding system needed to safely handle the entire electrical load of the building.

Part 3 & 4 use more aggregate calculation methods than part 2. This means it may be appropriate to use methods like "demand factors", which allow you to size the system based on the idea that not all loads will be running at their maximum capacity at the same time.

Key Question

Based on all the circuits I'm planning in my building (or section), what is the total load? Therefore, how big do my service entrance conductors, service disconnect, feeder conductors, and panelboards need to be to handle it all?

Think of it this way

You start with the planned loads (calculated in Part 2 and then aggregated in Part 3 and 4) and determine the minimum size for the feeders, service, and panels. This ensures the overall electrical system can handle the entire load safely and reliably.

In summary



Part 2

Individual circuits; load determination for a circuit. Focuses on protecting individual circuits.

Part 3 & 4

Feeders and Services; sizing the overall electrical system to handle the total load. Focuses on protecting the entire system.

Important Considerations: There is a lot of interplay between these sections. You can't accurately size a service without first understanding the loads that will be connected to branch circuits. Demand factors can only be applied to feeder and service conductors. They cannot be applied to branch circuit calculations. Many other articles of the NEC also apply and you can't ignore those. For example, you would need to know if derating the conductors would be needed due to bundling or high ambient temperature.By understanding this distinction, you'll be much better equipped to navigate the NEC's complex calculations and ensure you're designing safe and code-compliant electrical installations. Good luck with your studies! Flag for review