Short answer: Article 110 holds the rules that apply to almost every installation. Equipment must be approved and installed per its listing instructions. A termination limits the ampacity you may use to the temperature rating of the lowest-rated part of the connection, unless the NEC allows an adjustment. Equipment must be marked and labeled. And panels need clear working space: typically 3 feet deep for common low-voltage panelboards, at least 30 inches wide (or the width of the equipment, whichever is greater) and 6.5 feet high.
Workspace questions test whether you can pick the right voltage-to-ground row and the right condition. The PSI outline lists Workspace Clearance under Electrical Equipment and Devices, a 10-item area of the Texas Journeyman NEC Knowledge part. The Texas Journeyman Practice Pack has 1,000 practice questions on the 2026 NEC with lookup aids for finding each table in your own book. US$39 once.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the code in our own words and do not reproduce NEC text. Always read the rule in your own 2026 NEC and follow your supervisor and the local inspector.
Why Article 110 comes before everything else
Article 110 sits in Chapter 1, so it applies to every installation unless a later chapter changes it. Texas adopted the 2026 NEC effective September 1, 2026, and the TDLR exams moved to the 2026 NEC on the same date (TDLR rule adoption notice, PSI Candidate Information Bulletin). A few Article 110 rules changed in 2026, so older study guides can be wrong on the details below.
Article 110 map
| Topic | What it asks in plain words | Where to look |
|---|---|---|
| Approval | Conductors and equipment must be acceptable to the inspector. | Article 110 (approval) |
| Listing instructions | Install and use listed equipment the way its listing and labeling instructions say. In 2026, the instructions can be stricter than the code but cannot be weaker. | 110.3(B) |
| Interrupting rating | Fuses and breakers must be able to interrupt the fault current available at their line terminals. | 110.9 |
| Damaged equipment | Do not install equipment with damaged parts that could affect safe operation. | 110.12(B) |
| Terminal temperature | The ampacity you use is limited by the lowest temperature rating of the wire, the terminal or the device. | 110.14(C) |
| High-leg marking | On a 4-wire delta system, the high leg is marked orange. | Article 110 (high-leg marking) |
| Arc-flash marking | Service and feeder equipment, other than in dwelling units, gets a field or factory arc-flash warning. | 110.16 |
| Disconnect labels | Each disconnecting means is marked to show what it serves. | 110.22 |
| Available fault current | Service equipment in other than dwelling units is marked with the available fault current and the date it was calculated. | 110.24 |
| Working space | Clear space in front of equipment that may be examined, adjusted, serviced or maintained while energized. | 110.26 |
The 2026 changes in this list come from the City of Denison’s summary of 2026 changes: installation instructions cannot be less strict than the code, arc-flash marking now covers service and feeder equipment in general instead of only large equipment, and working-space depth is now measured from the enclosure front cover (Denison 2026 NEC summary).
Working space: depth, width and height
Depth depends on two things: the voltage to ground and what is behind you when you face the equipment. The code calls the three situations Conditions 1, 2 and 3 (Table 110.26(A)(1)). The table below shows two example rows. Read the full table in your own 2026 NEC for other voltages.
| Voltage to ground | Condition 1 | Condition 2 | Condition 3 |
|---|---|---|---|
| 150 volts or less | 3 ft | 3 ft | 3 ft |
| 277 volts (for example, a 480Y/277V system) | 3 ft | 3.5 ft | 4 ft |
- Condition 1: exposed live parts on one side, and nothing live or grounded on the other side (or the other side is insulated).
- Condition 2: exposed live parts on one side, grounded parts on the other. Concrete, brick and tile walls count as grounded.
- Condition 3: exposed live parts on both sides of the working space.
Width is at least 30 inches or the width of the equipment, whichever is more, and doors and hinged panels must be able to open at least 90 degrees. Headroom is at least 6.5 feet or the height of the equipment, whichever is more. There is also a dedicated space above and below panelboards and switchboards for electrical use only (110.26(E)). Pipes and ducts that do not serve the electrical equipment do not belong there.
Worked example 1: a 480Y/277 V panelboard
A 480Y/277 V panelboard, 20 inches wide, is mounted on a wall. The space in front of it faces a concrete block wall.
- Voltage to ground: 277 V. That is the 277-volt row.
- Condition: live parts on the panel side, grounded concrete on the other. Condition 2.
- Depth: 3.5 ft, or 3.5 × 12 = 42 inches, measured from the enclosure front cover.
- Width: the panel is 20 inches, which is less than 30. Width is 30 inches.
- Headroom: 6.5 × 12 = 78 inches, unless the equipment is taller.
Check: if the facing wall were drywall on wood studs with nothing grounded, it would be Condition 1 and the depth would drop to 3 ft (36 inches). 42 − 36 = 6 inches of difference, which is what concrete costs you.
Worked example 2: a 120/240 V house panel
A 120/240 V single-phase panel faces a concrete basement wall.
- Voltage to ground: 120 V. That is the 150-volts-or-less row.
- Every condition in that row is 3 ft, so depth is 3 ft (36 inches) whether the wall is concrete or not.
- Width: 30 inches or the panel width, whichever is more.
Worked example 3: terminal temperature limits ampacity
You pull 8 AWG copper THHN (a 90°C wire) to a breaker whose terminals are rated 75°C.
- From Table 310.16, 8 AWG copper is 40 A at 60°C, 50 A at 75°C and 55 A at 90°C.
- The lowest rating in the connection is the 75°C terminal, so you use the 75°C column (assuming no other termination or equipment limit applies): 50 A before any adjustment or correction.
- The 55 A value in the 90°C column can be used only as a starting point for derating, not as the final ampacity at a 75°C terminal.
Check: if the equipment were marked only for 60°C, the ampacity would drop to 40 A. Lowest rating wins every time: 40 is less than 50, and 50 is less than 55.
What this means on the job
- Read the label and the instructions before you mount or connect anything. Torque values, conductor ranges and terminal ratings are in them.
- Never stack material, carts or ladders in front of a panel. Working space must stay clear, not only on inspection day.
- Mark disconnects so the next person can tell what they control.
- If you see a pipe or duct running through the dedicated space above a panel, tell your supervisor. Moving it is easier before the ceiling goes in.
Check yourself
Our own practice questions. Answers below each.
- A 208Y/120 V panel faces a concrete wall. What is the minimum depth? Answer: 120 V to ground is in the 150-volts-or-less row, so 3 ft.
- A 480Y/277 V switchboard has exposed live parts on both sides of the aisle. What depth? Answer: 277 V is the 277-volt row, Condition 3: 4 ft, or 48 inches.
- A disconnect enclosure is 36 inches wide. What working-space width do you need? Answer: 36 inches, because it is more than 30.
- 10 AWG copper THHN lands on 60°C terminals. Which column sets the ampacity? Answer: The 60°C column, 30 A.
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The code book for working space and general requirements
NFPA 70, National Electrical Code (NEC), 2026 Edition, softbound. Article 110, including Table 110.26(A)(1), is in it. Read each section in your own copy before you rely on it.
FAQ
How much working space is required in front of an electrical panel?
For most panels with 150 volts or less to ground, at least 3 feet deep, 30 inches wide or the width of the equipment, and 6.5 feet high. For higher voltages to ground, such as 277 volts, the depth is 3, 3.5 or 4 feet depending on what is on the other side of the space. Read Table 110.26(A)(1) in your own 2026 NEC for other voltages.
What are Conditions 1, 2 and 3 for working space?
They describe what is across from the equipment. Condition 1 has nothing live or grounded on the other side. Condition 2 has grounded parts such as a concrete wall. Condition 3 has exposed live parts on both sides.
Why can’t I use the 90°C ampacity for THHN?
Because the terminals on breakers and devices usually have a lower rating. The NEC limits ampacity to the lowest temperature rating in the connection, which is often 60°C or 75°C.
Do installation instructions override the NEC?
No. Listed equipment must be installed according to its instructions, and the 2026 NEC makes clear those instructions can add requirements but cannot be less strict than the code.
Sources checked October 2026
- TDLR rule adoption notice, 2026 NEC: https://www.tdlr.texas.gov/news/rulemaking/2026/09/01/commission-adopts-rules-12/
- TDLR exam page: https://www.tdlr.texas.gov/electricians/elecexam.htm
- PSI Candidate Information Bulletin for TDLR (updated 9/15/2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- City of Denison, 2026 NEC significant changes: https://denisontx.gov/DocumentCenter/View/4131/2026-National-Electrical-Code-Significant-Changes
- NFPA 70 (NEC), 2026 edition, Articles 110 and 310, read in your own copy: https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70
