A panel is protected by one device, and knowing which one is the question
Article 408 is short. The parts that get tested are the ones that interact with other articles.
On this page
What protects the panel
A panelboard has to be protected by an overcurrent device with a rating not greater than that of the panelboard.
That device can sit ahead of the panel or inside it, and where it sits changes what else applies.
A question describing a panel and a feeder is usually asking whether the arrangement described satisfies that requirement.
The backfed device rule
A plug-in overcurrent device that is backfed and supplies power to a panel has to be secured in place by an additional fastener.
The reasoning is physical. A backfed breaker stays energised when the panel is de-energised from the main, so someone pulling it off the bus gets a surprise.
This appears constantly in questions about solar interconnections and about subpanels fed from the load side.
Where it meets other articles
- Working space. Article 110 governs the clearance in front of the panel and it fails more installations than the panel rules do.
- Grounding. Whether the neutral bonds to the can depends on whether this is service equipment, which is Article 250.
- Conductor sizing. The feeder to the panel is sized under the ordinary conductor rules, not under Article 408.
That last one catches people. Article 408 does not tell you what size wire to run.
The distinction the exam likes
Service equipment versus a subpanel. Everything about bonding, grounding and disconnect counting changes between them.
The question to ask is where the power came from. Directly from the utility service makes it service equipment. From another panel does not.
If a transformer sits between, the analysis resets, because a separately derived system creates a new service point of its own.
What this page cites
- NEC 408.36 Overcurrent protection of a panelboard.
- NEC 408.4 Circuit directory and field marking.
- NEC 110.26 Working space, which governs the room around it.
- NEC 250.24 Whether the neutral bonds here or not.