Burial depth on the Texas exam, and why cover and trench depth are two different numbers

What the exam asks about it

Underground work reaches a Texas journeyman paper from both halves. In our 500 question bank, 51 items sit in the conduit and raceway area, and four go under the ground: one works a trench depth from a cover figure, one asks what splitting a pull between two raceways does to the cover, and two turn on what the wet interior of a buried raceway does to the conductors and to the fill.

Seven more sit in the wiring methods area, covering what the cover requirement turns on, why the code sets cover at all, why a small residential circuit is allowed less of it, which conductors may go in the ground bare of any raceway, what a handhole in a lawn has to be, and how the inside of an outdoor raceway is classified.

The shape of a burial item is steady. It hands you a wiring method, a place, and sometimes a circuit description, and it wants one number back. Electrical wiring methods and materials carries 10 of the 56 scored items on the knowledge portion, tied for the heaviest single area, at about 2.2 minutes an item.

Cover and trench depth are two numbers

The arithmetic item is short and it catches people every year. A raceway with an outside diameter of 2.4 inches goes underground where 18 inches of cover is required, and the question asks how deep the trench has to be. Cover is measured from the top surface of the buried raceway up to finished grade, and the pipe lies on the bottom of the trench, so the trench carries the cover plus the outside diameter: 18 plus 2.4 is 20.4 inches.

Each wrong answer is a way that goes astray. 15.6 inches subtracts the diameter, the same arithmetic run backward. 22.8 inches adds it twice, above the raceway and below. 18 inches digs to the cover figure and leaves the top of the pipe 2.4 inches shy, which is the version that gets built.

Two details decide it under pressure. The figure you add is the outside diameter, and on rigid conduit that runs larger than the trade size, so reaching for the trade size lands you close, plausible and short. And cover runs to finished grade, concrete or similar cover, so grade cut down later in a landscaping plan takes the cover with it.

Reading the table by its words

Minimum cover for work at 1000 volts and below sits in a table inside NEC 300.7(A). Its columns are mostly wiring methods, running from the least protected thing you can put in the ground to the most protected, and its rows describe what lies over the run. Notes are printed beneath it, and one of them defines cover.

Hold the logic and the cells look after themselves. Mechanical protection around the conductor buys a shallower trench, because depth stands in for protection. That gives you a check needing no memory at all: an answer putting metal conduit deeper than bare direct burial cable is wrong before you look anything up.

Two of the columns describe circuits, and a circuit that fits one of them is read in that column whatever the pipe is made of. One covers a residential branch circuit at a limited voltage with ground-fault protection and a small overcurrent device. The other covers irrigation control and landscape lighting circuits at low voltage in identified cable or raceway. Both carry qualifying figures that have to be met first. A candidate who reads past the circuit description lands in the general column and answers deeper than the code asks, which is a wrong answer that feels safe.

Match the rows on their words too. The dwelling row says one and two family, so an apartment complex parking lot belongs with streets and parking lots. The scenario names a place in trade language and the table names it in code language.

What moves the cover figure

One bank item asks what the cover requirement turns on, and the answer is the wiring method used together with the surface the run passes under. Conductor size, soil type and the presence of an equipment grounding conductor are all offered and all fail. Cover is a mechanical requirement, which is why it never scales with the conductors inside the pipe.

A second item makes the same point from the field. A heavy pull crosses under a driveway, and the designer splits the conductors between two raceways of a smaller trade size. The cover required stays exactly where it was, since the table is entered by the wiring method and the kind of location. What the split does change is the fill calculation, now with two raceways to satisfy, and the conductor count adjustment in each one, which our page on conduit fill works through.

A third item asks why cover exists at all, and the answer is to keep digging and the loads above from reaching the run. The distractors are habits people bring to a trench: frost depth from plumbing, conductor temperature from the ampacity rules, and the water table. The code sets no frost depth for electrical work, and earth temperature belongs with conductor sizing and ampacity.

The inside of a buried raceway is wet

NEC 300.7(B) settles the conductor question before any depth question comes up, since the interiors of enclosures and raceways installed underground are wet locations. A companion item makes the same point above ground, where a conduit on an outside wall exposed to weather has a wet interior whatever the weather is doing, because the raceway breathes with the temperature and condenses inside.

Two items follow that into arithmetic. A pull of five conductors totals 0.335 square inches against a permitted 0.345 and fits. The run is then extended underground, the wet location calls for a conductor type listed for wet use, and that type carries an area of 0.0730 square inches each. Five times 0.0730 is 0.365 against 0.345 permitted, so the pull that fit above ground fails below it. The fill share holds steady underground, and the number that moved sits on the conductor side.

In the second, a raceway runs along a wall, turns down and continues underground to a remote building with the conductors pulled in one length. One conductor carries one insulation type end to end, so the whole length is chosen for the most demanding location it passes through. Splicing where the raceway enters the ground answers nothing, since a splice underground brings requirements of its own.

The short paragraphs around the table

The table is one item on the paper and the paragraphs around it are the rest, each short enough to be an item on its own.

• Coming out of the ground. Direct buried conductors and cables emerging from grade are protected by enclosures or raceways from the cover depth below grade up to at least 8 feet above finished grade, with that protection required to reach no more than 18 inches below grade (NEC 300.7(D)(1)). Items put the protection's start or finish in the wrong place, so read both ends.
• The warning ribbon. Direct buried service conductors and underground service raceways that go in without concrete encasement, at or below a stated depth, have their location identified by a warning ribbon in the trench above them (NEC 300.7(D)(3)). The 2026 edition added the raceways.
• Under a building. Cables under a building go in a raceway that extends beyond the outside walls (NEC 300.7(C)), and the table carries its own row for that run, so the two work together. An answer quoting the cover row alone is half an answer.
• Splices, backfill and seals. Direct buried cables and conductors may be spliced or tapped without a splice box, under the general splicing rule in Article 110 (NEC 300.7(E)). Material that could damage the raceway or cable stays out of the trench (NEC 300.7(F)), raceways through which moisture may contact live parts are sealed or plugged (NEC 300.7(G)), and the conductors of one circuit, including any equipment grounding conductor, go in the same raceway or cable, or close together in the same trench (NEC 300.7(I)).

What may go in the ground

The bank also asks what may actually be buried. Individual THWN conductors proposed for direct burial in a trench with no raceway fail, because only conductors identified for burial may be used that way. A wet location rating covers a conductor sitting in water inside a raceway and answers nothing about soil chemistry, backfill pressure and decades in the ground, which is why Types UF and USE exist as separate types.

Where the run is broken for a splice in a handhole set in a lawn, NEC 314.30 treats the handhole as a box you work in from grade: built for the loads where it sits, with the cover marked so nobody opens it looking for a water valve, and with metal covers and exposed conductive surfaces bonded. Our page on boxes and conduit bodies carries the rest of Article 314.

Where a feeder runs underground from a house panelboard out to a detached garage, Article 225 asks for a readily accessible disconnect at the garage, because the rule is about control and anybody working in that building has to be able to kill everything in it on the spot.

What to do before test day

Get the address right first. Minimum cover for work at 1000 volts and below sits at NEC 300.7(A) in the 2026 book, where the 2023 book carried it at 300.5(A). Article 300 moved down two sections this cycle, so an older tab set lands you two sections short, inside the same article, on real code text about something else. Most of what is published about burial depth still points at 300.5, so study from your own book.

Systems above 1000 volts sit in Article 305, with their own underground section at 305.15, so a medium voltage scenario is a different lookup. You can confirm both addresses from inside the book: NEC 250.64(B)(4) excuses grounding electrode conductors in contact with the earth from complying with 300.7 and 305.15, and the pair of sections a grounding conductor is excused from is the pair that governs burial.

Texas adopted the 2026 National Electrical Code effective 1 September 2026 under 16 TAC 73.100, and the PSI bulletin puts the examinations on that edition from the same date. The local layer matters on the job, since a city may adopt local amendments under Tex. Occ. Code 1305.201(c) and work inside the corporate limits complies with applicable local ordinances under subsection (d). Our page on local rules sets out what a city may require of you.

The worked table lookups and the arithmetic live in the question set. The thirty free timed questions here put burial items next to fill and support items.

Questions people ask

How deep does the trench have to be for 18 inches of cover?

Deeper than 18 inches by the outside diameter of the raceway. Cover is measured from the top surface of the buried raceway up to finished grade, and the raceway lies on the bottom of the trench, so a pipe with an outside diameter of 2.4 inches in a location requiring 18 inches of cover puts the trench at 20.4 inches. Digging to the cover figure leaves the top of the raceway 2.4 inches shy of what the table asked for. Use the outside diameter for that addition, since on rigid conduit it runs larger than the trade size.

What does the minimum cover requirement turn on?

The wiring method used and the surface the run passes under. The cover table at NEC 300.7(A) has wiring methods in its columns and what lies above the run in its rows, so the same cable under a driveway and under a lawn give two different figures. Conductor size has no part in it, soil type has no part in it, and an equipment grounding conductor in the trench changes nothing. Two of the columns describe circuits, and a circuit that fits one of them is read in that column whatever the pipe is made of.

Does splitting a pull between two raceways reduce the cover?

No. Cover is set by the wiring method in the column and the kind of location in the row, and neither the trade size nor the number of raceways is one of those inputs, so dividing a heavy pull between two smaller raceways leaves the required cover exactly where it was. What the split does change is the fill calculation, which now has two raceways to satisfy, and the conductor count adjustment, since each raceway carries fewer current-carrying conductors. The trench may finish shallower in absolute terms, because a smaller pipe adds less of its own diameter.

Can THWN conductors be direct buried in Texas?

Only conductors identified for burial may be installed in the ground with no raceway around them, and a wet location rating is a different thing. A wet location rating covers a conductor sitting in water inside a raceway, and it answers nothing about soil chemistry, backfill pressure or decades in the ground. Types UF and USE carry the burial listing, which is why they exist as separate types at all. Adding depth changes nothing here either, since no amount of cover makes an unlisted conductor suitable for direct burial.

Why do conductors in a buried raceway have to be rated wet?

NEC 300.7(B) makes the interiors of enclosures and raceways installed underground wet locations, so the conductors pulled into them are listed for wet use. That reaches a run pulled in one continuous length, which carries one insulation type from end to end and has to suit the most demanding location it passes through. It also reaches the fill calculation, because insulation thickness varies by type and the same wire size can carry a different area, so a pull that fit above ground can fail once the wet location forces a different conductor type.

Where is the burial table in the 2026 code book?

At NEC 300.7(A). The 2023 book carried the same material at 300.5(A), and Article 300 moved down two sections in the 2026 edition, so a tab set cut for the older book lands two sections short inside the same article. Texas adopted the 2026 edition effective 1 September 2026 under 16 TAC 73.100 and the examinations moved to it on the same date. Systems above 1000 volts sit in Article 305, with their own underground section at 305.15, so a medium voltage scenario is a separate lookup.