Luminaires under roof decking

In a commercial occupancy, lighting fixtures were installed directly onto the metal decking roof above. The roof is poured concrete and not insulated. The owner is questioning this installation, saying there needs to be space between the metal deck and the lighting fixture. Is that correct?

See Section 410.10(F), which provides requirements for luminaires installed under roof decking. The general requirement is that where a luminaire is subject to physical damage from screws in the roof decking, it must be installed so there is a minimum of 1½ inches between the lowest surface of the roof decking and the top of the luminaire. It is important to note that this requirement, along with the installation of cables, raceways or boxes installed under roof decking, applies only where a metal one with removable insulation is installed [see 300.4(E)]. 

These roofs are designed to be replaced after the initial installation and the self-­tapping screws used to secure the roof typically penetrate up to 1 inch below the lowest surface of the roof decking. These roofs are easy to identify—just look up for the screw penetrations. See the exception to 410.10(F) and exception No. 2 to 300.4(E), which state that the 1½-inch spacing is not required where metal roof decking is covered with a minimum thickness of 2 inches of concrete slab, measured from the top of the corrugated roofing.

Minimum SPD rating? 

In the state where we do most of our work, the 2020 NEC goes into effect in July. We now need to install surge protective devices (SPDs) for all services in dwelling units. They are not all the same, so what is the minimum requirement for the SPD? Why is this in the Code? The NEC is not a design manual; if a homeowner wants an SPD to protect their TV, let them do it, but this should not be a Code requirement. 

Section 230.67 was new in the 2020 NEC and was limited in scope to dwelling units. As revised in the 2023 edition, this requirement applies to all dwelling units, dormitory units, guest rooms and guest suites of hotels and motels, and areas of nursing homes and limited-care facilities used exclusively as patient sleeping rooms. 

The 2020 NEC does not contain a minimum SPD rating. The 2023 revisions include a minimum performance requirement for the SPD installed. The SPD must have a nominal discharge current rating of not less than 10 kA. The requirement’s intent was not to protect a TV or computer installed in these locations, but to protect ground-fault circuit interrupters, arc-fault circuit interrupters, smoke alarms and other sensitive electrical equipment installed to save lives. 

Large equipment requirements

Does the Code require a door at each end of the working space where five service disconnects are installed? An engineer’s note references NEC Section 110.26(C) on the single line drawing. However, there is no single piece of equipment rated at 1,200A or more. There are two 200A and two 400A fused disconnects for a 480V–277V service.

Yes, the 110.26(C)(2) requirements apply in this installation. This requirement mandates that all large equipment that contains overcurrent devices, switching devices or control devices under conditions 110.26(C)(1) or 110.26(C) (2) be installed with a means of entrance and egress at each end of the working space. 

List item 110.26(C)(1) applies to all (feeder or service supplied) equipment rated 1,200A or more and over 6 feet wide. List item 110.26(C)(2) applies only where more than one service disconnect is installed as permitted in 230.71(B). 

Where this occurs, the installer must add the amp ratings and width of each service-disconnecting means. Where the combined amp ratings are 1,200A or more and the combined width is 6 feet or more, two means of egress are required. 

As stated in your question, the combined amp rating is 1,200A. There are five fusible disconnecting means that, on average, will be 20–24 inches wide and result in a width of 100 inches or more (more than 6 feet). Where the installation allows a continuous and unobstructed way of egress travel, or the depth of the working space is twice that required by 110.26(A)(1), a single entrance to the working is permitted.

GFCI for twist-lock receptacle?

An inspector flagged us for not providing GFCI protection for a 240V, 50A, twist-lock receptacle in a commercial kitchen. It is our understanding that the GFCI requirements in 210.8 do not apply to twist-lock receptacles. Was the inspector correct to flag this?

Yes, see the parent text of Section 210.8(B), which requires GFCI protection for all 125V through 250V receptacles supplied by single-­phase branch circuits rated 150V or less to ground, 50A or less, and all receptacles supplied by three-phase branch circuits rated 150V or less to ground, 100A or less. The requirement makes no reference to the type of receptacle. Additionally, there are six exceptions, none of which reference twist-lock receptacles.

Optional standby system capacity

How do we determine the minimum capacity for an optional standby generator? Do we need to perform calculations, or can we use peak demand in the venue over the last few years?

Section 702.4 contains requirements for optional standby system capacity. Where the transfer of power to the optional system is manual [see 702.4(A)(1)], the system must have adequate capacity and rating for the supply of all equipment intended to be operated at one time. In a manual transfer scenario, the optional standby user can select the loads connected to the system. Manual transfer equipment requires human intervention. If the transfer switch is automatic, the system capacity must be capable of supplying the full load that is automatically connected, or an energy management system can be installed to automatically manage the connected load. Additionally, 702.4(A)(2) permits the optional system capacity to be determined by another approved method that may include peak service demand.

SE cable for EV charger?

Is 6 AWG copper type SE cable permitted for EV charger installation branch circuits where the charger is rated at 48 full-load amps? It is our understanding that 6 AWG copper in Romex would not be permitted due to continuous load requirements.

Yes, 6 AWG copper Type SE cable is permitted to supply electric vehicle supply equipment (EVSE) rated at 48 full-load amps. Section 625.41 requires that overcurrent protection for branch circuits supplying EVSE be sized for continuous duty with a current rating of not less than 125% of the equipment’s maximum load. 

An overcurrent device rated at 60A is required as 125% of 48A equals 60A. All EV charging loads are considered continuous for the purposes of Article 625; see 625.42. Branch circuits that supply continuous loads must have an ampacity of 125% of the continuous load as required in 210.19. A full-load current of 48A requires branch circuit conductors rated at 60A. Six AWG copper Type SE cable has a 75°C ampacity of 65A, while 6 AWG copper Type NM cable must have a 60°C ampacity and is only rated at 55A, rendering it noncompliant for the continuous load of 60A. 

Type SE installed as a branch circuit for interior installations is required by 338.10(B)(4) to be installed in accordance with Part II of Article 334, except for the ampacity requirements in 334.80. This requires that Type NM cable is limited to 60°C ampacity values in all cases, while Type SE cable can be applied at 75°C ampacities. 

Transformer clearance

To allow for proper ventilation of a 150-kVA dry-type transformer installed in the corner of an electrical closet, how much space is needed and how far must it be installed from each wall?

The NEC requires that ventilation of transformers be provided to dispose of transformer full-load heat losses to prevent a temperature rise that is more than the transformer rating (Section 450.9). For ventilation openings to operate properly, minimum clearances must be provided. Typical clearances for dry-type transformers range from 2–12 inches from an adjacent wall. The required minimum clearance distance will be marked on each transformer nameplate. See Section 450.11(A) for required marking information. List item 450.11(A)(6) requires clearances for transformers with ventilation openings be marked on the transformer nameplate.

Jim Dollard