Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at firstname.lastname@example.org. Answers are based on the 2020 NEC.
Closet LED fixtures
Are surface-mounted, LED lighting fixtures permitted to be installed in a dwelling-unit clothes closet?
Section 410.16(A)(3) permits surface-mounted fluorescent or LED luminaires to be installed in a clothes closet, provided the fixtures are identified as suitable for installation in a clothes closet. See the Article 100 definition of “identified.” The associated informational note provides the Code user with examples of how to determine suitability for use in a clothes closet, including (1) the fixture can be investigated and listed or labeled as suitable, (2) approved by an inspection agency or (3) approved by an organization concerned with product evaluation.
Fill for hazardous location seals?
For work in a Class I, Division II location, what is the maximum number of 12 AWG THHN conductors we can install in ¾-in. seal-off fittings? Can we fill them to 40%, same as conduit fill?
Article 501 contains requirements for Class I installations with sealing and drainage requirements located in 501.15. See the requirements in 501.15(C) that contain requirements for all seals in Class I, Divisions I and II locations.
Subsection 501.15(C)(6) mandates that the cross-sectional area of conductors in a seal cannot not exceed 25% of the raceway’s cross-sectional area unless the seal is specifically identified for a higher percentage of fill. Manufacturer’s specifications must be obtained to make a determination. The conductor fill limitation is necessary to ensure that the sealing compound can fill all of the spaces between conductors to limit the passage of gas. Some seals are limited to 25% fill, while others go as high as 40% fill.
The method to determine maximum fill is similar to basic conduit fill calculations. For example, ¾-inch rigid conduit has a total area (see Chapter 9, Table 4) of 0.549 square inches. 0.549 x 0.25 = 0.13725. A single 12 AWG THHN conductor (see Chapter 9, Table 5) is 0.0133 square inches. 0.13725/0.0133 = 10.3. Maximum fill would be (10) 12 AWG THHN conductors. Note that for seals identified at 40% fill, the values in Annex C can be applied and (16) 12 AWG THHN conductors are permitted in a ¾-inch seal specifically identified for 40% fill.
Service conductor taps in a wireway
Four retail occupancies in a strip mall are being supplied from a single set of service conductors by a service lateral with taps made in a wireway. They are separated by masonry firewalls and are permitted to be service supplied. Do we need to comply with the tap rules in 240.21(B)?
No, the requirements in 240.21(B) apply only to feeder taps. The conductors in your question are not feeders; they are service conductors. Clarity is found in the definition of “tap conductor” in 240.2. A tap conductor is a conductor “other than a service conductor” that has overcurrent protection ahead of its point of supply exceeding the value permitted for similar conductors that are protected, as described elsewhere in 240.4.
Replacing circuit breakers
An insurance company notified a client of ours that they were not going to renew their current policy unless existing circuit breakers identified as problematic were replaced and then inspected by a third party. We did just that. During the electrical inspection, we were informed that existing multiwire branch circuits (two single-pole devices) required handle ties or common trip circuit breakers. We disagreed, but were forced to comply. Isn’t this an overreach by the inspector?
No, the inspector was correct. The NEC is not a retroactive document. However, the act of replacing existing circuit breakers with new devices requires compliance with the NEC in effect at the time of replacement. Two single-pole circuit breakers are not permitted to supply a multiwire branch circuit unless identified handle ties are installed. See 210.4(B), which requires each multiwire branch circuit to be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates. Any circuit breaker or device replacement requires compliance with all NEC rules in effect at the time of replacement.
SER cable as feeder
When installing SER cable in a dwelling unit, are we limited to the 60°C (140°F) ampacity, as done with Romex? In some municipalities, they allow ampacity at 75°C (167°F), while others enforce 60°C ampacity. Can you help?
Part II of Article 338 contains requirements for the installation of Type SE cable. Section 338.10(B) addresses the installation of Type SE cable when used as branch circuits or feeders. Section 338.10(B)(4) requires compliance with Part II of Article 334, excluding Section 334.80. This mandates compliance with all of the installation requirements for Type NM cable. Section 334.80 allows ampacity derating for Type NM cable to begin at the 90°C (194°F) ampacity (see 334.112), but limits Type NM cable overcurrent protection to the 60°C ampacity. Type SE cable is not limited to the 60°C ampacity because compliance with 334.80 is specifically excluded in 338.10(B)(4), allowing Type SE cable to use the 75°C ampacity value.
Metal wireways installation
Are metal wireways required to be listed? We were questioned about this by an owner. We had to custom-cut the wireway and install chase bushings to go directly into a panelboard. Their claim is that the listing is violated once we cut and punched holes. Additionally, we installed the wireway through a wall, and the owner insisted we transition to conduit within the wall. What is permitted?
Throughout Chapter 3 of the NEC (and elsewhere), the 3XX.6 section is used for listing requirements. Metal wireways are covered in Article 376 and nonmetallic wireways in Article 378. It is significant to note that while there are no listing requirements for metal wireways, 378.6 requires nonmetallic wireways and associated fittings to be listed.
Metal wireways are not required to be listed, because it is very common to custom cut and fabricate these raceways, including their covers and end plates. The act of punching holes in any type of wireway for the entry of conduits, cable assemblies, chase bushings, etc., is not a violation of the NEC or the listing of nonmetallic raceways.
Metallic and nonmetallic wireways are permitted to pass “transversely” through walls, provided the length through the wall is unbroken and access to the conductors within the wireway is maintained on both sides of the wall. Wireways through walls must be installed transversely, meaning crosswise (for example at a 90-degree angle to the wall). See 376.10(4) and 378.10(4).
SPGFCI for temporary power?
Is it still permitted to use a special-purpose ground fault circuit interrupter (SPGFCI) for receptacles installed for temporary power at 208V, 30A?
No, 590.6(B) no longer permits the use of an SPGFCI. In the 2017 NEC , 590.6(B)(2) permitted an SPGFCI for outlets other than those covered by 590.6(A)(1) through (A)(3). During the 2020 NEC revision cycle, the permission to use a SPGFCI in 590.6(B)(2) was deleted to coordinate with actions taken by the committee with general purview over GFCIs during the 2017 revision cycle.
SPGFCIs operate well above the thresholds for Class A GFCIs, which will open when ground fault current is 6 milliamps (mA) or higher and will not open when ground fault current is less than 4 mA. SPGFCI devices open only on higher values of ground fault current. This would allow enough ground fault current to flow through the body at values above the “let go threshold” without opening. GFCI-type circuit breakers are readily available at 208V, 30A. Additionally, 590.6(B)(2), which permits an Assured Equipment Grounding Conductor Program, can be applied.