Texas Electrician ExamTexas journeyman & master

Checked against primary sources 2026-08-24

One device protects the panel, and Article 408 will not size your wire

Article 408 is short and most items built on it are really testing another article. Knowing which one is most of the work.

On this page
  1. What protects the panel, and where that device sits
  2. How many disconnects, and why six handles in one can is not the answer
  3. The back-fed device rule, said properly
  4. The terminal bar, and the conductor that gets it to itself
  5. The places a panel is barred from
  6. The room in front of it and the column above it
  7. Service equipment or subpanel, and the question that settles it
  8. What this page cites

What protects the panel, and where that device sits

A panelboard has to be protected by an overcurrent protective device with a rating not greater than that of the panelboard, and that device can be inside the panel or at any point on its supply side (NEC 408.36).

So a stem describing a 225 ampere panelboard fed through a 200 ampere breaker in the switchgear upstream is compliant on this point, and a 400 ampere panelboard fed from a 400 ampere main is compliant too. What fails is the panelboard whose rating is below the device ahead of it, which is why the first thing to read in one of these items is the two ratings and nothing else.

The exceptions are narrow and worth reading in your own book rather than recalling. One covers a panelboard protected on its supply side by two main circuit breakers or two sets of fuses whose combined rating does not exceed the panelboard, and it says in other than service equipment. Another is an allowance for an existing panelboard used as service equipment for an individual residential occupancy.

Be careful with older study material here. The exception that used to release a service panelboard with multiple disconnecting means from individual protection came out of 408.36, and the arrangements in 230.71 do that work now. A candidate reasoning from the deleted exception will pick a confidently wrong option.

One thing 408.36 does not do is protect the conductors feeding the panel. That is an ordinary conductor problem answered from Article 240 and the ampacity rules, and an item that hands you a feeder size along with a panel rating is usually testing whether you know the two questions are separate.

How many disconnects, and why six handles in one can is not the answer

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

The old picture of six main breakers sharing one panelboard is not one of the arrangements the subsection lists. If your memory of the six disconnect rule is a single can with six handles in it, that memory is older than the book you will sit with, and it fails in the field as well as on paper.

Read 230.71(A) too, because it tells you what does not count toward the six. Disconnecting means installed as part of listed equipment and used solely for power monitoring, for a surge-protective device, for the control circuit of a ground-fault protection system, or for operating a power-operable service disconnect are not service disconnecting means for this purpose. An item that shows you seven handles and expects a violation is often showing you six plus one of those.

The back-fed device rule, said properly

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 has to be secured by an additional fastener that requires something other than a pull to release it from its mounting (NEC 408.36(D)).

Three words in that carry the whole rule. Additional, so the normal mounting is not it. Other than a pull, so a stiffer clip is not it either, and what the rule wants is 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 rather than procedural. A back-fed device stays energized from its own supply after the panel is killed at the main, so anyone who pulls it off the bus expecting it to be dead gets a surprise on both stabs.

Article 705 relaxes it in one place. Where the power output circuits can only operate in interactive mode, a plug-in-type circuit breaker is permitted to leave off the additional fastener that 408.36(D) would otherwise want (NEC 705.30(E)). The logic is that an interactive source stops producing when it loses the grid, so the breaker it feeds goes dead when it leaves the bus. A source that can carry an island does not get that relief, and an item that describes storage rather than a straight interactive inverter is testing the difference.

The terminal bar, and the conductor that gets it to itself

Each grounded conductor terminates within the panelboard in an individual terminal that is not also used for another conductor (NEC 408.41). Two neutrals under one screw is the violation, and it is a violation whether or not the screw is tight, because two neutrals sharing a lug means lifting one circuit opens the return path of another.

The exception is for the grounded conductors of circuits with parallel conductors, which are permitted to share a terminal identified for more than one conductor. Identified for it is the condition. An ordinary bar is not.

Equipment grounding conductors are a separate bar. Where wire-type equipment grounding conductors enter the cabinet they land on a grounding terminal bar bonded to the cabinet, not on the neutral bar (NEC 408.40).

Whether the two bars are tied together is decided upstream, not in Article 408. At the service disconnect an unspliced main bonding jumper connects the grounded conductor to the equipment grounding conductors and the enclosure (NEC 250.24(C)). Past that point a grounded conductor may not be reconnected to ground on the load side of the service disconnecting means except where Article 250 permits it (NEC 250.24(B)), which is why the bonding screw comes out of a subpanel.

The places a panel is barred from

These rules live in Article 240 rather than Article 408, because what the code restricts is the location of overcurrent devices, and the panel is only illegal because of what is inside it. Candidates who look for a location rule in 408 do not find one and lose the item.

Overcurrent protective devices may not be located in the vicinity of easily ignitible material, such as in clothes closets (NEC 240.24(D)).

Overcurrent protective devices other than supplementary overcurrent protection may not be located in bathrooms, showering facilities, or locker rooms with showering facilities (NEC 240.24(E)).

That one has moved on from what a lot of study material says. The restriction is written to the room, not to the occupancy, so a bathroom in a commercial building or a locker room with showers in it is covered on the plain words, and older material saying it applies only in dwelling units, dormitories and guest rooms is describing a narrower rule than the one in the book you will sit with.

Overcurrent protective devices may not be located over the steps of a stairway (NEC 240.24(F)).

And they have to be readily accessible, with the center of the grip of the operating handle in its highest position not more than 6 feet 7 inches above the floor, grade or working platform, unless one of the listed cases applies (NEC 240.24(A)). Read the cases. There is more than one and they are how the exceptions get written into items.

The room in front of it and the column above it

Two Article 110 rules apply to every panel and they are not the same rule. In front of the panel there has to be working space a person can stand in, sized by voltage and by what is on the other side of that space. Above the panel, in its own footprint, there is a zone that belongs to the electrical installation and not to the mechanical trades.

For an exam item the useful habit is to check both whenever a stem bothers to describe the room. A stem that mentions a ceiling height, a pipe, a duct or what is stacked on the floor is spending words for a reason.

Service equipment or subpanel, and the question that settles it

Ask where the conductors landing on the panel came from, because almost everything about bonding and about how many disconnects you may have turns on the answer.

Service equipment is a defined term in Article 100 and not a judgment call. It is 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 is not that, whatever the label on the door says.

A transformer sitting between does not make a service either. It makes a separately derived system, and the bonding for one is done under 250.30 with a system bonding jumper rather than under 250.24 with a main bonding jumper. The service point, which is the point of connection between the serving utility’s facilities and the premises wiring, is upstream of all of it, and nothing you install inside the building creates another one.

That distinction is worth being precise about, because a stem that puts a transformer in the middle is usually checking whether you will call the downstream panel service equipment. It is not service equipment. It is the first panel of a separately derived system, and the rules it answers to are in Article 250 Part II.

What this page cites

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