Written against the 2026 NEC and checked section by section, September 2026
Enclosure Types Practice Questions
An enclosure-type number is a statement about the conditions the box was tested against, not a grade, and the numbering does not behave like a ladder. These questions work what NEC 110.28 requires to be marked and what it says the enclosures do not protect against, how Table 110.28 is entered by condition and read across, the pairs of types that differ by one row, and the rules in Articles 110, 300, 314, 404 and 409 that spoil a correctly chosen enclosure after the fact.
Pick an answer and the explanation opens with the section it comes from. These are original questions written for this site, not questions from the exam. Have your own code book open: the Texas exam is open book, and looking the section up is the skill being tested.
Read the enclosure types study page first if the topic is new to you.
1. What does an enclosure-type number tell you?
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B. Which environmental conditions the enclosure was tested to keep out
The number is a claim about conditions and nothing else. It says this box was tested against a particular set of things arriving in a particular way, and it says nothing about gauge, finish or quality. Read as a list of conditions the subject is straightforward, and read as a quality scale it stays confusing forever.
NEC 2026 110.28
2. Which of these is named in the list of equipment whose enclosures have to carry an enclosure-type marking?
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C. A meter socket
The section lists switchboards, switchgear, enclosed panelboards, industrial control panels, motor control centers, meter sockets, enclosed switches, transfer switches and a good deal more. It opens by excluding surrounding fences and walls in as many words. Luminaires and receptacles are covered by their own articles rather than by this marking requirement.
NEC 2026 110.28
3. What does the enclosure-type section say these enclosures are not intended to protect against?
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C. Condensation, icing, corrosion or contamination that arises inside the enclosure or enters through the raceway or unsealed openings
That one sentence is worth more on the job than anything else in the section. Picking the right type does nothing about water arriving up the conduit from a wet trench, so an item that describes an underground run into an outdoor enclosure may be asking about that rather than about the number on the door. The other three options are conditions the table actually addresses.
NEC 2026 110.28
4. Table 110.28 is used for selecting enclosures for use in specific locations, with one category of location excluded. Which one?
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A. Hazardous classified locations
The table is titled Enclosure Selection and covers ordinary indoor and outdoor conditions. Classified locations are handled by the Chapter 5 articles, which is also where the product standard puts its third group of types. The table itself splits into an outdoor half and an indoor half, so neither of those is excluded.
NEC 2026 110.28, Table 110.28
5. What is the first move on an enclosure selection item?
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B. Write down the location in the code's own words and turn that into the specific conditions the table is indexed by
The table is indexed by condition rather than by type, so the words in the stem describing where the equipment is going are the entry point. Rain is one condition, a hosedown is another and airborne dust is a third, and the description has to be sorted into those terms before any type number is useful. Field habit is what the item was written for, since the habit is right most of the time and not all of the time.
NEC 2026 Table 110.28
6. Which enclosure type in Table 110.28 is the only one shown as protecting against prolonged submersion?
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C. Type 6P
Temporary submersion and prolonged submersion are two separate rows and only one type carries the second. Type 6 stops at temporary, which is the practical difference between a box that survives being flooded and one that is meant to live under water. Type 4X is a hosedown and corrosion type, and Type 3S is about sleet.
NEC 2026 Table 110.28
7. Two outdoor enclosure types differ on the submersion rows and agree almost everywhere else. Which pair is it, and which row separates them?
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D. Types 6 and 6P, separated by prolonged submersion
Both of those carry temporary submersion and only the second carries prolonged submersion. That is the pattern the whole table is built on, one number with a suffix that adds one property, and it is why an option list built from one family with one letter changed works so well as a distractor. Types 4 and 4X are separated by corrosive agents rather than by water.
NEC 2026 Table 110.28
8. An outdoor enclosure has to keep out windblown dust as well as rain. Which of these does the table show as covering both?
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A. Type 3
Rain, snow and sleet is one row and windblown dust is a separate row, and the two types part company on the second one. A type built to shed falling rain was never asked to keep out driven dust, so it does not, and the number being larger changes nothing. This is the cleanest proof that the numbering is not a ladder.
NEC 2026 Table 110.28
9. A disconnect outdoors has to have its operating mechanism work after it is covered in ice. Which row of Table 110.28 carries that, and which types satisfy it?
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B. The sleet row with its footnote, satisfied by the types built for sleet
Two different sleet conditions appear in the outdoor half. One is grouped with rain and snow and is about keeping weather out, and the separate sleet row carries a footnote about the mechanism still being operable when ice covered. Only the types built for that condition satisfy the second one. Reading the footnotes is part of reading the table.
NEC 2026 Table 110.28
10. Types 4 and 4X are shown identically across most of the table. Which row separates them?
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D. Corrosive agents
The letter suffix marks an added property, and here that property is resistance to corrosive agents. Both types carry hosedown and both carry windblown dust, so those rows cannot be doing the work. Two types with the same number and different letters are not interchangeable in either direction, which is the point of the suffix.
NEC 2026 Table 110.28
Ten down. If you want these timed and scored by content area, the practice exam runs thirty questions free, and the full bank of 178 plus the calculation ladder is $79 once.
11. Which indoor enclosure type does Table 110.28 show as protecting against oil or coolant spraying and splashing?
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D. Type 13
The indoor half carries two oil rows. Seepage is the milder one and several types answer it, while spraying and splashing is answered by one type only. That distinction is what separates a control enclosure that lives near a machine from one that lives on it. A hosedown type is a water type and is not shown against either oil row.
NEC 2026 Table 110.28
12. An indoor enclosure has to survive both a washdown with a hose and oil seepage from nearby machinery. What does Table 110.28 show?
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A. No single type shown in the indoor half carries both the hosedown row and the oil seepage row
The hosedown row is answered by the water types and the oil seepage row is answered by the oil types, and the indoor half does not put both on any one type. That is exactly the case where an item is testing a second condition you have not spotted yet, and the answer is to go back to the stem rather than to pick whichever type appears in two options. The ancillary markings named in the informational notes exist for combinations like this.
NEC 2026 Table 110.28, 110.28
13. Types 1 and 2 differ on one row of the indoor half of Table 110.28. Which condition is it?
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B. Falling liquids and light splashing
Both carry incidental contact and falling dirt, and neither carries the dust rows. The one row that separates them is light dripping and splashing from above, which is the difference between a box in a clean electrical room and a box under a pipe. Neither is anywhere near a washdown condition.
NEC 2026 Table 110.28
14. A control enclosure sits in a room with lint circulating in the air. Which of these does Table 110.28 show as answering that condition?
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C. Type 12
The indoor half separates circulating dust, lint, fibers and flyings from settling airborne dust, lint, fibers and flyings, and the two rows do not always agree. Type 5 answers the settling row and not the circulating one, which is the trap here since both types read as dust types on a spec sheet. Types 1 and 2 answer neither row.
NEC 2026 Table 110.28
15. Does a higher enclosure-type number carry everything a lower number carries?
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D. No, the families overlap in places and diverge in others
The product standard groups the types by intended use rather than by rank, into indoor only, indoor or outdoor, and the hazardous location group that sits apart from both. Once you have seen the design test list the odd behavior of the numbering stops being odd, because each type is a particular subset of that list. Reading the table as a scale is what produces confident wrong answers on this subject.
NEC 2026 110.28, Table 110.28
16. A knockout is removed from a panelboard enclosure and never filled. What does Article 110 require of the closure?
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C. That it afford protection substantially equivalent to the wall of the equipment
The standard the closure has to meet is written against the wall of the equipment it sits in, which is a performance test rather than a product list. An open knockout turns a rated enclosure into an unrated one no matter what the marking on the door still says. Openings intended for equipment operation, for mounting, or permitted as part of a listed design are not unused openings.
NEC 2026 110.12(A)
17. A metallic plug is used to close an unused opening in a nonmetallic enclosure. What extra condition applies?
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B. It has to be recessed at least 1/4 inch from the outer surface of the enclosure
The recess keeps the metal away from anything on the outside of a nonmetallic box, which is the reason the sentence exists at all. It is a dimension worth tabbing because nothing about it is intuitive and it appears in a section people read as general workmanship language. The bonding option sounds right for metal in an enclosure and is not what the section says.
NEC 2026 110.12(A)
18. An enclosure marked for one set of conditions is installed carefully in a location it was never tested against. What does Article 110 say?
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D. Listed equipment is installed and used in accordance with the instructions in its listing or labeling, and the type marking is part of what was listed
The listing carries the conditions, so the marking is not a suggestion that good practice can override. This is where field experience actively works against a candidate, because the electrician who has installed the same enclosure on four hundred outdoor jobs has a fast confident answer available. The rule is short and it is the one the item is built on.
NEC 2026 110.3(B)
19. A box is installed in a wet location and fed by a fitting that is not suited to wet locations. What does Article 314 require?
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A. Boxes, conduit bodies, outlet box hoods and fittings installed in wet locations are listed for use in wet locations
The requirement names the fittings alongside the boxes, so a wet location enclosure fed through a fitting that is not is still a wet location problem. A separate subsection asks that boxes, conduit bodies and fittings in damp or wet locations be placed or equipped to keep moisture from entering or accumulating inside. What comes into the box has to come in through hardware suited to the same conditions.
NEC 2026 314.15
20. A drain opening is made in the field in a box listed for use in a wet location. What size range does Article 314 permit?
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A. Not smaller than 1/8 inch and not larger than 1/4 inch in diameter
Both ends of the range matter. Too small and it clogs, too large and it becomes an entry for the things the enclosure was rated to keep out. Larger openings are permitted where a listed drain fitting is installed according to its instructions, which is the route to take when the small hole is not enough.
NEC 2026 314.15
21. Exposed wiring, boxes and fittings are installed in an indoor wet location such as a dairy processing room. What does Article 300 require of the mounting?
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D. That there be at least a 1/4 inch airspace between the equipment and the wall or supporting surface
The airspace lets the wall and the back of the enclosure dry and drain rather than holding water against the metal, and it applies to the whole exposed wiring system including boxes, cabinets, fittings, raceways and cable. An exception releases nonmetallic raceways, boxes and fittings from it. Picking an enclosure type does nothing about the surface it is screwed to.
NEC 2026 300.8
22. Enclosures for industrial control panels are selected on what basis?
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A. Table 110.28, for locations other than hazardous classified locations
The construction part of that article points straight back at the same table and repeats the warning that these enclosures are not intended to deal with condensation, icing, corrosion or contamination arising inside or entering through the conduit. So the method does not change when the equipment does. The short-circuit rating is a separate marking requirement in the same article.
NEC 2026 409.100
23. Outdoor electrical equipment covered by the working space rules has to meet which installation requirement?
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D. It is installed in a fenced area
The outdoor subdivision opens with a short list and the first entry asks for identified enclosures, which ties the working space rules back to the enclosure selection question. Height above grade, canopies and fences appear elsewhere in Article 110 for other purposes and are not what this entry says. Wrong answers on this item are all real rules attached to the wrong section.
NEC 2026 110.26(E)
24. A surface-mounted switch or circuit breaker is installed in a damp or wet location. What does Article 404 require?
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C. That it be enclosed in a weatherproof enclosure or cabinet meeting the cabinet article's damp and wet location rules
The switch article hands the question to the cabinet article, which asks that surface-type enclosures in damp or wet locations be placed or equipped so that moisture and water are kept from entering and accumulating. A cover plate on its own does not do that. Following the pointer to the other article is the whole task here.
NEC 2026 404.6, 312.4
25. Trade terms such as raintight, rainproof, watertight and dusttight appear in an informational note under the enclosure-type section. What is that note doing?
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B. Explaining which type numbers each of those trade words is typically used with
The note maps everyday trade vocabulary onto the type numbers, which matters because a specification or a supplier will say rainproof when the table itself says nothing of the kind. Explanatory material of this sort is not enforceable on its own, and a separate note in the same section is the one that points at the international ingress protection ratings. The word to sort by on an item is still the condition in the stem rather than the trade term.
NEC 2026 110.28, 90.5(C)
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