Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to firstname.lastname@example.org. Answers are based on the 2020 NEC.
Cutting into solid rock
Where nonmetallic conduit is installed under a driveway, the Code requires 24 inches of burial depth. We are bidding a job in an area that is known to have solid rock just below the surface. Do we need to cut into the rock to get to the required burial depth?
No. The requirements for installing raceways underground are in Section 300.5. The installation you described—nonmetallic raceways listed for direct burial—generally requires a burial depth of 18 inches and 24 inches where under a driveway, in accordance with Table 300.5. Always read the table notes; they are Code requirements, not just informational notes. Table 300.5, Note 5, permits a metal raceway, or a nonmetallic raceway permitted for direct burial, to be installed under 2 inches of concrete extending down to rock where solid rock prevents compliance with the general cover depths.
An inspector is requiring documentation of identification for barriers between 277 volt (V) switches. We purchased the barriers—sold as “voltage partitions”—from the junction box manufacturer. The inspector said that a listing mark would work, but there are no listing marks on the barriers. What documentation can I provide?
The requirement you are referring to is in 404.8(B) that requires identified barriers securely installed between adjacent devices where the voltage between the switches will exceed 300V. The definition of “identified” in Article 100 does not contain a requirement or require listing. Identified means that the product is recognizable as suitable for the specific purpose, function, use, environment or application. The informational note that follows the definition provides examples of ways to determine suitability, including investigations by a qualified testing laboratory (listing and labeling), an inspection agency or other organization concerned with product evaluation. No documentation is required. Many NEC requirements mandate identified products, but each requirement is different. In this case, you purchased an identified product from the manufacturer of the boxes you were using. There are many identified products available that will be suitable for the purpose without regard to who made it. The key is that it is suitable for the specific purpose or application required in the NEC .
Bare conductor ampacity
On my state exam, there was a question about the ampacity of multiple insulated conductors and one bare conductor. Table 310.16 only has ampacities for insulated conductors, and Table 8 in Chapter 9 does not contain ampacities. Where do we find bare conductor ampacity?
Section 310.15 contains requirements for the application of the ampacity tables in Article 310. 310.15(D) requires that bare or covered conductors installed with insulated conductors will have a temperature rating equal to the lowest temperature rating of the insulated conductors in the same raceway or enclosure. For example, consider a bare conductor installed in a raceway with RHW and RHW-2 insulated conductors. RHW is rated at 75°C (167°F) and RHW-2 is rated at 90°C (194°F). In this case, the bare conductor would have an ampacity of a 75°C-rated conductor.
Pool motors GFCI
The 2020 NEC requires Class A GFCI protection for swimming pool motors. Wasn’t that always required?
Yes. Text in the 2017 NEC required GFCI protection for personnel. The definition of GFCI in Article 100 that clearly states it is intended for the protection of people and must de-energize a circuit or portion thereof within an established period of time when a ground-fault current exceeds the values established for a Class A device. The revision is essentially redundant. The committee responsible added the revised “Class A GFCI” text in an effort to keep pool installers from using a special-purpose GFCI, which does not operate at the same current levels as a GFCI.
There are several other changes in this requirement. It now very clearly applies to the “outlet” supplying the pool motor and not the entire branch circuit. Additionally, it provides clarity by requiring GFCI protection for all pool motors on branch circuits rated 150V or less to ground and 60A or less, single- or three-phase.
What is required to mark junction boxes for emergency systems? In the past, we would just mark the cover plate with the circuit number from an emergency panelboard such as “EL1A Circuit #15.” This was called into question on a current job, and we were asked to spray-paint the emergency boxes and plates red. Is that required?
The requirement for identification of emergency system wiring in 700.10(A) is to permanently mark emergency circuits so they will be readily identified as a component of an emergency circuit or system. The requirement provides two marking methods. The first deals with equipment and not wiring methods. Boxes and enclosures including, but not limited to, transfer switches, generators, etc., for emergency circuits must be permanently marked as a component of an emergency circuit or system. A panelboard, transfer switch or switchboard can easily be labeled as “emergency.” However, marking a junction box cover plate with a circuit number, the word “emergency” or “EM,” for example, does not meet the requirement to permanently mark. Spray-painting junction boxes and covers (typically, red for emergency) is a means of permanent-marking. Section 700.10(A) also requires that where boxes or enclosures are not encountered, exposed cable or raceway systems must be permanently marked to be identified as a component of an emergency circuit or system at intervals not to exceed 25 feet. This is another marking requirement that is easily met with spray paint. Receptacles supplied from the emergency system must also be identified with a distinctive color or marking (typically, red) on the receptacle cover plates or the receptacles.
Covering handhole enclosures
Are handhole enclosures permitted to be covered with stone to eliminate tripping hazards?
The general rule in 314.29(B) requires that handhole enclosures be installed so they are accessible. It is not permitted to install them below sidewalks, paving, earth or other materials used to establish the finished grade. However, an exception permits listed boxes and handhole enclosures to be covered if their location is effectively identified and accessible. The exception permits gravel, light aggregate or noncohesive granulated soil to cover the box or handhole. This would, for example, allow the handhole to be quickly accessed after removing a layer of gravel or light stone.
Knockout plugs for holes
An inspector had me remove a blank, 4-inch junction box cover and replace it with a 1¼-inch knockout plug. The inspector informed us that knockout plugs were required for holes up to a 2-inch trade size because those sizes are readily available at the supply house. I cannot find such a requirement in the Code!
The requirement for unused openings is that they be closed to afford protection substantially equivalent to the wall of the equipment. See 110.12(A). This requirement does not apply to holes that exist for mounting purposes or those permitted as part of the design for listed equipment to ventilate, etc. The NEC does not specifically require a knockout plug. This is intentional, as unused openings can vary in size, including trade sizes ½-inch through 6 inches, 12-inch-by- 12-inch wireway openings and larger. While a knockout plug is easier to install, a blank plate installed so that it does not impact installed conductors would be permitted.