Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code to Jim at [email protected]. Answers are based on the 2023 NEC.

Range calculations

I am running calculations for a building with 18 large apartments. Each apartment has a range/oven rated at 18 kW. The ranges are single-phase, and the system is 208/120V. I know Section 220.55 applies here, but I am struggling to come up with the maximum demand. Can you help?

Section 220.55 permits the ranges in this installation to be calculated in accordance with Table 220.55. Note that the last sentence in this section requires that where two or more single-phase ranges are supplied by a three-phase, four-wire feeder or service, the total load must be calculated on the basis of twice the maximum number of ranges connected between any two phases.

In this installation, to balance the load over 18 units, six ranges will be supplied between A/B phases, six between A/C phases and six between B/C phases. Therefore, twice the maximum number of ranges connected between any two phases is 2 x 6 = 12. When applying Table 220.55, column C is used for individual ranges rated not over 12 kW.

Since the ranges here are over 12 kW, we must apply Table Note No. 1. This note applies to ranges individually rated more than 12 kW but not more than 27 kW and that are the same rating. This note allows the use of column C values in Table 220.55, provided the maximum demand is increased by 5% for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW. We have 18 ranges, and the maximum demand in column C for 18 ranges is 33 kW. This value must be increased by 5% for each kilowatt over 12. In this case, the individual ranges are 6 kW over 12 and 6 x 5% = 30%. The column C value of 33 kW is then increased, 33 x 1.3 = 42.9. The calculated demand for the ranges is 43 kW.

Plastic anchors

At a local Code meeting some time ago, the chief inspector informed us that plastic anchors were prohibited to secure electrical equipment to a wall or structure of any type. We have looked everywhere and have even contacted our local utility company to see if a similar prohibition exists for mounting meter enclosures and can find no such requirement. Are plastic anchors permitted to support electrical equipment?

The NEC does not contain any requirements that prohibit plastic anchors. In some installations, plastic anchors are the most feasible and practical method available. See Section 110.13(A), which addresses equipment mounting and requires it to be firmly secured to the surface it is mounted on. This section does prohibit the use of wooden plugs driven into holes in masonry concrete plaster or similar material. 

GEC to transformer

When installing smaller dry-type transformers, we have always taken the grounding electrode conductor (GEC) through an existing vent opening toward the bottom of the transformer to prevent drilling another hole in the enclosure. Another contractor told me that is a Code violation. We cannot find it; can you help?

Requirements for the installation of GECs are found in Section 250.64. See 250.64(G), which prohibits the installation of a GEC through a ventilation opening in any enclosure, not just transformers.

Life safety branch loads?

It is our understanding that the life safety branch in a hospital is limited to lighting in egress hallways and exit stairways. Our drawings show lighting and some receptacles from life safety in a room with standby generators. Is that permitted?

In a healthcare facility, the essential electrical system is made up of separate branches designed to supply a limited amount of lighting and power to loads considered essential for life safety while enabling hospital staff to stop or pause procedures if normal power is lost. The essential electrical system consists of the equipment, life safety and critical branches. Section 517.33 lists the functions and loads permitted to be connected to the life safety branch, including illumination necessary to egress the building, exit signs, alarm/alerting systems such as fire alarm and medical gas alarms, necessary communication systems during emergency conditions, elevators and automatic doors.

Also included in the permitted life safety loads are generator set locations. This allows lighting, power to battery chargers, receptacles at the generator set location and receptacles at transfer switches that are part of the essential electrical system. Generator accessories such as fuel transfer pump(s), ventilation fans, electrically operated louvers, controls, cooling system and other generator accessories essential for generator operation are permitted to be connected to the life safety branch or to the output terminals of the generator through overcurrent protective devices.

Pool house feeder

Does a feeder supplying a panelboard for branch circuits to pool equipment in a commercial occupancy require an insulated copper equipment grounding conductor (EGC)?

The requirements for where an insulated copper EGC must be installed in accordance with Article 680 for swimming pools have been revised over the last few NEC cycles with significant clarity added. See Section 680.7(A), which requires that feeders and branch circuits installed in a corrosive environment or wet location must contain an insulated copper EGC. 

Wet locations include any area unprotected and exposed to weather, areas subject to saturation, all conductors underground and conductors in concrete slabs or masonry in direct contact with the earth. A corrosive environment is an area used for storage, handling or dispensing of pool sanitation chemicals that does not have adequate ventilation, thereby exposing electrical equipment to corrosion. 

Where a corrosive environment exists, Section 680.14(A) requires wiring methods that are suitable for corrosive environments. This section recognizes RMC, IMC, rigid PVC, RTRC and LFNMC as suitable for use.

Overhead service conductors

Section 230.23(A) has language in it that requires overhead service conductors to be sized in accordance with Article 220. We recently installed a 600A 208/120V service with parallel 500 kcmil aluminum conductors. However, the utility brought over what looks like a single 1/0 aluminum conductor that connects to parallel 500 kcmil. The owner questioned me on that and wanted to know why I installed conductors that were so large. What do I tell the owner?

The answer is found in the definitions in Article 100. It is important to inform the owner that the utility company is not bound by NEC rules. The section (230.23(A)) you reference in your question is not applicable.

This section is in Part II of Article 230, “Overhead Service Conductors.” The NEC has purview over premises wiring, which begins at the service point and is the point of connection between the serving utility and the premises wiring. The overhead conductors described in your question are service drop conductors because they are owned and installed by the utility. The NEC applies from the service point downstream and includes the premises wiring.

The section you referenced does not apply to service drop conductors, it applies to overhead service conductors, which would be part of the premises wiring, if installed. Overhead service conductors are installed where the utility ends at a pole, for example, and more poles are added to get the overhead service conductors to the building or structure supplied.

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