Clean backfill material

Does the Code require pea gravel or an equivalent when backfilling buried PVC conduit?

No, if you have clean backfill that does not contain large rocks, paving materials, cinders, large or sharply angular substances or corrosive material, no additional steps are required. Where there are large rocks or other material that could damage the buried raceways, etc., the raceways must be protected, and one method would be granular material such as pea gravel. See Section 300.5(F).

Splice in a disconnecting means?

Does the NEC prohibit splicing in a disconnecting means? The venue is a small industrial facility and a 600V, 200A, nonfusible disconnect is proposed. The disconnect exists only to facilitate the removal of power from two controllers (loads spliced) with one throw of the hand. These are not taps.

No, the NEC does not prohibit splices inside of a disconnecting means enclosure; it contains a permissive requirement allowing splices in a disconnecting means under prescriptive conditions. See Section 404.3(B), which contains a general rule prohibiting splices in a disconnect unless the requirements of 312.8 are met. Where this requirement is properly applied, a disconnecting means may contain splices or feed-through conductors.

Section 312.8 addresses enclosures that contain switches or overcurrent devices. This rule is often discussed where splices occur in a cabinet containing a panelboard. Splices are permitted where (1) the total of all conductors installed at any cross section of the wiring space does not exceed 40% of the cross-sectional area of that space, and (2) the total area of all conductors, splices and taps installed at any cross section of the wiring space do not exceed 75% of the cross-sectional area of that space.

Where feed-through conductors meeting the above requirements are installed, a warning label complying with 110.21(B) must be placed on the disconnect enclosure to inform maintenance personnel that feed-through conductors exist. This permissive requirement would also permit power monitoring or energy management equipment installed in a disconnecting means in accordance with 312.8(B).

Metal studs and Type NM cable

How can I support Romex vertically where metal studs are installed?

Type NM cable installed in metal studs must meet the requirements of Section 300.4(B)(1) to protect the cable. This requires listed bushings or grommets for all factory or field-cut holes in the metal studs. The protection must cover all metal edges. There are multiple devices readily available to secure NM cable vertically. Other solutions could include cable ties that come with a hole to secure it to the metal stud or other approved method.

Bonding conductor size?

On a set of engineered drawings, there are multiple raceways (EMT) run between IT closets that contain engineered bonding conductors for telecommunications equipment. The raceways will contain a single 500 kcmil copper to bond grounding bus in each closet. We understand the need for bonding the conduit, but does it have to be a 500 kcmil copper?

The conductors referenced in your question are bonding conductors, and the sizing and installation is primarily governed by the designing engineer or other referenced standards. Where run in a ferrous metal raceway, such as EMT, grounding/bonding conductors must be bonded at each end with bonding jumpers. In this case, the size of those bonding jumpers is a design issue and the designing engineer should be consulted. 

The only NEC requirement for full-size bonding jumpers is where a grounding electrode conductor is installed in a ferrous metal raceway. In that case, 250.64(E)(3) applies and a full-size (or larger) bonding conductor is required.

Reduced conductor size

In a dwelling unit, there is an existing 200A service with a 100A feeder to a downstream panelboard. I am installing an optional standby system with an ATS to supply only specific loads. My drawing showed the normal feeder and load conductors of the ATS to the 100A panelboard as 2 AWG aluminum. Plan review says the NEC requires 1 AWG aluminum. I thought the NEC permitted reduced sizes?

The permitted reduction in conductor sizes referenced in your question is found in Section 310.12. This requirement permits service and feeder conductors to be reduced to 83% of the feeder or service rating where these conductors supply the entire load associated with a single-family dwelling. In your installation, the 100A feeder conductors are not supplying the entire load and must be fully rated. See Section 310.12 and the associated table.

Hard-piping transformer connections

An inspector failed a transformer installation on one of our jobs and we had to change from direct connection with EMT to flexible metal conduit. The 75 kVA transformer had vibration isolators inside that isolated the enclosure. Is hard-piping a transformer an NEC violation?

No, the NEC does not require flexible conduit where a transformer is installed. In some cases, project specifications and/or the manufacturer’s instructions or manufacturer’s suggested best practices may require a flexible connection.

Receptacles in a wet location

In a three-season room (sunroom), there are receptacle outlets on a masonry knee wall below screens to the backyard. The township wants weatherproof receptacles and in-use bubble covers. Is that really necessary?

Yes, the receptacles in your question are installed in a wet location (direct contact with water). Rain will obviously go through the screen to some degree and then down onto the receptacles. See Section 406.9(B)(1) that requires receptacles installed in wet locations to be weather-resistant type and installed in an enclosure that is weatherproof with or without an attachment plug installed. This requires an outlet box hood as defined in 406.2.

Working space clearance

The wording of 110.26 has us tripped up a bit. In an existing building (replacement only) the working space distance is just a bit too small with panelboards on both sides. Can we ignore the panelboard covers and measure from bus to bus? That would get us where we need to be.

No, see the parent text of 110.26(A)(1), which states that the working distance must be measured from the enclosure if the live parts are enclosed. 110.26(A)(1)(c) may help in your situation. This requirement applies to existing buildings only where electrical equipment is being replaced. Where conditions of maintenance and supervision ensure that written procedures are adopted to prohibit equipment on both sides of the aisle from being open at the same time, and only authorized, qualified persons may service the installation, the distances in condition 2 (Table 110.26(A)(1)) can be applied.

Service equipment labeling

For the service equipment labeling in 110.16(B) at 1,200A, we used an incident energy analysis label as permitted by the exception. An inspector is demanding we include the date the label was applied. Is that correct?

No, the general rule in 110.16(B) for services rated at 1,200A or more is to label the nominal system voltage, the available fault current at the service overcurrent protective device and its clearing time and the date the label was applied. When the exception is applied, all that is needed is the labeling as seen in NFPA 70E Section 130.5(H), which does not require marking the date the label was applied. NFPA 70E does not require a date because the labeling must be monitored (reviewed for accuracy) and revised if changes in the electrical distribution system impact the label information. It is important to note that additional requirements include, but are not limited to, the general arc flash warning label in 110.16(A), arc energy reduction methods in 240.67 and 240.87 and GFPE protection if over 150V to ground and not over 600V phase-to-phase (typically 480/277V).