Short answer: Surface metal raceway (Article 386) is a metal raceway mounted on the surface of a wall or ceiling, often called by a manufacturer’s brand name on site. It is generally for dry locations and has a list of places it may not go, including where the voltage is 300 volts or more between conductors unless the metal is at least 0.040 inch thick nominal (NEC 386.12). The ampacity adjustment factors for more than three current-carrying conductors do not apply when all three conditions are met: the raceway’s cross section is more than 4 square inches, there are not more than 30 current-carrying conductors, and the conductors fill not more than 20 percent of the interior cross section (NEC 386.22). Splices and taps are permitted where the cover is removable and accessible, with fill at that point not over 75 percent (NEC 386.56).
PSI lists raceways in the Wiring Methods and Materials subject area of the Texas Journeyman exam: 10 scored NEC Knowledge questions and 2 scored Calculations questions. PSI does not say how many cover surface metal raceway. The Texas Journeyman Practice Pack has 1,000 original questions and 10 timed mock exams in the real two-part format, with step-by-step solutions for every calculation. Try free practice questions without signing up. Get the full pack for US$39 with one payment.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the ideas in our own words and do not reproduce NEC text. Check every rule and table value in your own 2026 NEC, and follow your supervisor and the local inspector.
Where it may and may not go
| Situation | Surface metal raceway |
|---|---|
| Dry location, exposed on a wall or ceiling | Permitted, with the other uses listed in 386.10 |
| Through a dry wall or floor, with the length through it unbroken | Permitted under the conditions in 386.10 |
| Where subject to severe physical damage | Not permitted unless otherwise approved (NEC 386.12) |
| 300 volts or more between conductors | Only if the metal is at least 0.040 inch thick nominal, or as otherwise allowed in 386.12 |
| Corrosive vapors, hoistways, or concealed, except as 386.10 allows | Not permitted; read the full list in 386.12 |
The 300 volt line is a favorite detail. A 277/480 V lighting circuit has 480 V between phase conductors, so ordinary thin-wall surface raceway needs the thickness condition or another allowance in 386.12 to carry it. Check whether the section’s wording covers listed products in your 2026 NEC.
Conductors, fill and derating
- Size and number. No conductor larger than the raceway is designed for, and no more conductors than it is designed for (NEC 386.21) (NEC 386.22). The manufacturer’s listing tells you those numbers.
- The derating exemption. The adjustment factors for more than three current-carrying conductors in 310.15 are not applied when all three conditions in 386.22 are met at once: cross section more than 4 square inches, not more than 30 current-carrying conductors, and fill not more than 20 percent (NEC 386.22). Miss one condition and you derate as usual.
- Support. Supported according to the manufacturer’s installation instructions (NEC 386.30).
Splices, taps and grounding
- Splices and taps are permitted inside the raceway where it has a removable cover that is accessible after installation. At that point, the conductors, splices and taps may fill not more than 75 percent of the cross section (NEC 386.56).
- Grounding. A surface metal raceway may serve as an equipment grounding conductor where it meets the conditions in 386.60 and 250.118, and where it transitions from another wiring method it needs a means to connect an equipment grounding conductor (NEC 386.60).
- Combination raceways. Where one raceway carries both power and signaling or communications circuits, the different systems run in separate compartments, identified for example by color coding of the interior finish (NEC 386.70).
Worked example: does the derating exemption apply?
A surface metal raceway has an interior cross section of 4.2 square inches. It carries 12 current-carrying 12 AWG THHN conductors. Use 0.0133 square inches per conductor as the practice value from Chapter 9, Table 5; check it in your 2026 NEC.
- Cross section. 4.2 is more than 4 square inches. Met.
- Count. 12 is not more than 30. Met.
- Fill. 12 × 0.0133 = 0.1596 square inches. 0.1596 ÷ 4.2 = 3.8 percent, not more than 20 percent. Met.
- Result. All three conditions are met, so no adjustment factor is applied under this rule.
Change the raceway to 3.5 square inches and condition 1 fails, so the 12 conductors are adjusted under 310.15.
Check yourself
- A raceway is 6 square inches and carries 32 current-carrying conductors at 15 percent fill. Is the exemption available? No. More than 30 conductors.
- What is the fill limit at a splice inside the raceway? 75 percent of the cross section at that point.
- Can ordinary surface metal raceway carry a 480 V circuit? Only if it meets the 0.040 inch thickness condition or another allowance in 386.12.
Disclosure: If you buy through the Amazon link below, Tsai Electro may earn a commission at no extra cost to you. As an Amazon Associate I earn from qualifying purchases.
Find Article 386 faster on exam day
NFPA 70, National Electrical Code, 2026 Edition (softcover). Number the three derating conditions in 386.22 in the margin as 1, 2 and 3, so you check all three before you skip the adjustment factor. The Texas exam is open book. PSI allows a soft-bound NEC with highlighting, underlining and notes made in advance. Loose-leaf, spiral-bound and ring-bound copies are not allowed, and only permanent index tabs made or supplied by the NEC publisher are permitted; homemade and third-party tabs are not.
FAQ
Is surface metal raceway allowed in wet locations?
Article 386 lists dry locations among its permitted uses. Check 386.10 and the product listing before using it anywhere else.
When do I skip derating in surface metal raceway?
Only when all three conditions in 386.22 are met: cross section more than 4 square inches, not more than 30 current-carrying conductors, and fill not more than 20 percent.
Can I splice inside surface metal raceway?
Yes, where it has a removable cover that is accessible after installation, with fill at the splice not over 75 percent.
Can surface metal raceway carry 480 volts?
Only where it meets the 0.040 inch nominal metal thickness condition or another allowance in 386.12.
Can power and data share a surface raceway?
Yes, in a combination raceway with separate compartments for the different systems, identified as 386.70 requires.
Sources checked October 2026
- PSI Candidate Information Bulletin, Texas electrician examinations (updated September 15, 2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- NFPA 70, National Electrical Code, 2026 Edition, Articles 310 and 386, and Chapter 9, Table 5
