One device protects the panelboard, and Article 408 will not size your feeder for you

Where panelboards sit on the paper

Panelboards spread across several subject areas on the Texas journeyman paper, which is why they feel bigger than their article. The PSI content outline gives electrical equipment and devices 10 of the 56 scored items on the NEC Knowledge portion, tied for the heaviest area, and control devices and disconnecting means carries 1 item on each portion. Services carries 6 knowledge items and 4 calculation items, many of which describe a panel.

Our 500-question bank puts numbers on the crossover. Eighteen questions name a panelboard and 17 of those sit in the installation knowledge area. Read their answers and the pattern is clear: the panelboard is in the stem, and the rule being tested comes from Article 230, 240, 250, 110 or 705 far more often than from Article 408.

That is the most useful thing to carry into the room here. A candidate who opens Article 408 for a panel question and finds nothing has spent a third of a 2.2-minute item on the wrong article, and both portions are scored separately at 70 percent with a $78 retake behind them.

One device protects the panel

A panelboard is protected by an overcurrent protective device rated no greater than the panelboard, and that device may sit inside the panel or at any point on its supply side, at NEC 408.36.

So a 225-ampere panelboard fed through a 200-ampere breaker in upstream switchgear complies on this point, and a 400-ampere panelboard on a 400-ampere main complies too. What fails is a panelboard rated below the device ahead of it, so the first thing to read in these items is the two ratings.

The exceptions are narrow. One covers a panelboard protected on its supply side by two main circuit breakers or two sets of fuses whose combined rating stays within the panelboard rating, and it is written for other than service equipment.

One thing 408.36 leaves alone is the conductors feeding the panel. That is an ordinary conductor problem answered from Article 240 and the ampacity rules, and an item handing you a feeder size with a panel rating is checking whether you keep the two questions apart, and feeders carries the conductor side of it.

Six handles in one can

Two to six service disconnects are permitted under NEC 230.71(B), and the arrangement matters as much as the count. Each one stands in its own enclosure, its own panelboard with a main service disconnecting means in it, its own switchboard enclosure or barriered vertical section, or its own compartment of switchgear or a metering center.

The old picture of six main breakers sharing one panelboard sits outside those arrangements. If your memory of the six disconnect rule is one can with six handles, that memory is older than the book you'll sit with.

Read NEC 230.71(A) alongside it for what falls outside the count: disconnecting means installed as part of listed equipment and used solely for power monitoring, for a surge-protective device, for a ground-fault protection control circuit, or for operating a power-operable service disconnect. An item showing seven handles and expecting a violation is often showing six plus one of those, and services works the group.

The back-fed fastener rule, said properly

A plug-in overcurrent device, or a plug-in main lug assembly, that is back-fed and terminates field-installed ungrounded supply conductors is secured by an additional fastener requiring something other than a pull to release it from its mounting, at NEC 408.36(D).

Three words carry the whole rule. Additional, so the normal mounting falls short. Other than a pull, so the rule wants a screw or a bracket. Field-installed, which is the trigger, and is why a factory main in a main breaker panel is a different situation from a breaker you fed backward on site.

The reason is physical. A back-fed device stays energized from its own supply after the panel is killed at the main, so anyone pulling it off the bus expecting it to be dead gets a surprise on both stabs. The distractor worth noting in our bank swaps the plug-in device for a bolt-in one: plug-in devices are permitted with the fastener, and the rule is written for them because a bolt-in device stays on the bus.

Article 705 relaxes it in one place. Where the power output circuits can only operate in interactive mode, a plug-in-type circuit breaker may leave off the additional fastener at NEC 705.30(E), since such a source stops producing when it loses the grid. A source that can carry an island keeps the fastener.

The two terminal bars

Each grounded conductor terminates within the panelboard in an individual terminal used by that conductor alone, at NEC 408.41. Two neutrals under one screw is the violation whether or not the screw is tight, because lifting one circuit then opens the return path of another. The exception covers the grounded conductors of circuits with parallel conductors, which may share a terminal identified for more than one.

Equipment grounding conductors get their own bar. Where wire-type ones enter the cabinet they land on a grounding terminal bar bonded to the cabinet, at NEC 408.40.

Whether the two bars are tied together is settled upstream. At the service disconnect an unspliced main bonding jumper connects the grounded conductor to the equipment grounding conductors and the enclosure, at NEC 250.24(C). Past that point a grounded conductor stays clear of ground except where Article 250 permits it, at NEC 250.24(B), which is why the bonding screw comes out of a subpanel.

Our bank has a Texas-common arrangement built on this: a dwelling with the meter and main disconnect outside and a panelboard inside fed from it. The jumper belongs in the outside enclosure, and the indoor panel is wired like any subpanel, with an isolated neutral bar and four wires in the feeder, and grounding and bonding carries the whole chain.

Where a panel is barred from

These rules live in Article 240, because the code restricts where overcurrent devices go and the panel is caught by what is inside it. Candidates who hunt for a location rule in Article 408 find nothing and lose the item.

• Overcurrent protective devices are kept away from easily ignitible material, such as in clothes closets, at NEC 240.24(D).
• Overcurrent protective devices other than supplementary overcurrent protection are kept out of bathrooms, showering facilities and locker rooms with showering facilities, at NEC 240.24(E).
• Overcurrent protective devices are kept off the steps of a stairway, at NEC 240.24(F).
• They are readily accessible, with the center of the grip of the operating handle in its highest position at 6 feet 7 inches or less above the floor, grade or working platform, unless a listed case applies, at NEC 240.24(A).

The bathroom rule has moved on from what a lot of study material says. The 2026 restriction is written to the room, so a commercial bathroom or a locker room with showers is covered on the plain words. NEC 240.24 also asks that each occupant have ready access to the devices protecting their own conductors, with named exceptions including buildings under continuous management supervision.

The room in front and the column above

Two Article 110 rules apply to every panel and they answer different questions. In front of the panel there has to be working space a person can stand in, sized by voltage and by what sits opposite, at NEC 110.26(A). Above the panel, in its own footprint, there is a dedicated space belonging to the electrical installation, at NEC 110.26(E).

The bank separates them cleanly. A water line running across the ceiling directly above a panel is a dedicated space problem, and the trap lines record the two misreadings: working space depth, measured out from the front, and working space height, measured up from the floor. Piping, ducts and other systems foreign to the electrical installation are kept out of that volume, with sprinkler protection the one thing the section makes room for.

Three more details the bank tests. Working space height runs from the floor to 6 feet 6 inches or to the top of the equipment where that is higher. Two panels on walls meeting at a corner may have overlapping working spaces, since the section asks for room a person can stand and work in. And the second entrance requirement turns on an ampere rating and a physical width together, with voltage playing no part.

Storage in front of a panel is the most common real-world violation in the code, because a space clear at inspection stops being clear once the building is occupied. Conduit, boxes and raceways carries the neighboring material.

Service equipment or subpanel

Ask where the conductors landing on the panel came from, because the bonding and the disconnect count both turn on the answer.

Service equipment is a defined term in Article 100: the equipment connected to the load end of the service conductors and intended to be the main control and cutoff of the supply. A panel fed from another panel falls outside that, whatever the door label says. A separately derived system sitting between makes the downstream panel the first panel of that system, bonded under NEC 250.30 with a system bonding jumper.

Two markings get confused here and the bank tests both. A panelboard marked suitable for use as service equipment tells you the assembly is listed for that use, including the means to bond the grounded conductor to the enclosure, and it does nothing to force the panel into that role. Separately, NEC 110.24 requires a field-applied marking at service equipment giving the available fault current and the date it was figured.

What to do before test day

Build the tab set around where the answers live, since Article 408 holds only a few of them.

• Tab 408.36 and 408.36(D) together, and put 408.40 and 408.41 on a second flag. Those four sections are most of what Article 408 gets asked for.
• Tab 230.71 and 240.24, the two articles panel questions run to. Write panel location on the 240.24 flag, because that is the one candidates hunt for in the wrong article.
• Tab 110.26(A) and 110.26(E) separately, since one rule is in front of the panel and one is above it.

Then practice the classification move: before reading the options, write one word in the margin naming the article the question belongs to. The worked arithmetic for panel and busbar questions lives in the question set, and this page is about picking the article fast enough to use it well.

Finish on a clock. Thirty free timed questions will show how often you open Article 408 for a question Article 240 owns, which is the habit to break before you pay the $78.

Questions people ask

Does the overcurrent device protecting a panelboard have to be inside it?

No. NEC 408.36 asks for an overcurrent protective device with a rating no greater than the panelboard, located in the panelboard or at any point on its supply side. So a 225-ampere panel fed through a 200-ampere breaker in upstream switchgear complies, and so does a 400-ampere panel with a 400-ampere main. What fails is a panelboard rated below the device ahead of it. The exceptions are narrow, and the one that used to release a service panelboard with multiple disconnecting means has left the section.

When does a back-fed breaker need an additional fastener?

NEC 408.36(D) reaches a plug-in overcurrent device or a plug-in main lug assembly that is back-fed and used to terminate field-installed ungrounded supply conductors. The fastener is additional to the normal mounting and has to require something other than a pull to release, so a screw or a bracket qualifies and a stiffer clip falls short. Article 705 relaxes it where the power output circuits can only operate in interactive mode, at NEC 705.30(E), because such a source stops producing when it loses the grid.

Why does the bonding screw come out of a subpanel?

Because the grounded conductor is bonded to the equipment grounding system at one place only. NEC 250.24(C) puts an unspliced main bonding jumper at the service disconnect, and NEC 250.24(B) keeps a grounded conductor clear of ground on the load side of that disconnect except where Article 250 permits it. In the common Texas arrangement with a meter and main outside, the jumper belongs in the outside enclosure and the indoor panel runs an isolated neutral bar, a bonded equipment grounding bar and a four wire feeder.

Can a panelboard go in a bathroom or a clothes closet?

The restrictions sit in Article 240 because the code is regulating where overcurrent devices go. NEC 240.24(D) keeps them away from easily ignitible material such as in clothes closets, NEC 240.24(E) keeps them out of bathrooms, showering facilities and locker rooms with showering facilities, and NEC 240.24(F) keeps them off stairway steps. The 2026 text of (E) is written to the room, so a commercial bathroom is covered on the plain words, which is wider than a lot of study material states.

How much of the Texas exam is panelboard material?

Less than it feels and more than Article 408 suggests. The PSI content outline gives electrical equipment and devices 10 of the 56 scored knowledge items, tied for the heaviest area, and control devices and disconnecting means 1 item on each portion. In our 500-question bank, 18 questions name a panelboard and 17 of them sit in the installation knowledge area. Read their answers and most are testing Article 230, Article 240, Article 250, Article 110 or Article 705.

What is the difference between working space and dedicated space?

Working space is the room a person stands in, in front of the equipment, sized by voltage and by what is on the opposite side, at NEC 110.26(A). Dedicated space is the volume above the equipment in its own footprint, running to a stated height or the structural ceiling, and systems foreign to the electrical installation are kept out of it, at NEC 110.26(E). A water pipe crossing the ceiling above a panel is a dedicated space problem. Working space height is measured up from the floor.