Commercial Garages, Plate Electrodes and More

By Jim Dollard | Jun 14, 2024
Car repair on a lift for the repair of the chassis, automatic transmission and engine in the auto repair shop or garage. Car workshop concept
During a routine building inspection, a building official informed the owners of a commercial garage that the wiring to a pump for a container of alcohol-based windshield washer fluid was a hazardous location.




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

Commercial garages

During a routine building inspection, a building official informed the owners of a commercial garage that the wiring to a pump for a container of alcohol-based windshield washer fluid was a hazardous location. We were called in to help and are confused. When we contacted the manufacturer of the windshield washer fluid, we were informed that it is diluted before being shipped and does not represent a hazardous location. Can you help?

See Section 511.3(E)(2), which states that areas for storage, handling or dispensing alcohol-based windshield washer fluid in repair garages are unclassified locations.

Plate electrode installation

Job specs require two plate-type electrodes in a dozen locations that are then bonded to structural steel at equidistant points. Are these to be installed similar to ground rods? Why would the engineer specify these? Are they available?

Electrodes permitted for grounding are identified in Section 250.52(A). Plate electrodes are specifically permitted in 250.52(A)(7) and are required to expose a minimum of two square feet of plate surface to the exterior soil. 

Plate electrodes made of coated iron or steel must be ¼-inch thick, and nonferrous metal plates must be 1/16-inch thick. Plate electrodes must be installed in accordance with 250.53(5), which requires them to be installed not less than 30 inches below the surface of the earth. 

The minimum spacing requirements for rod, pipe and plate electrodes in 250.53(B) mandate a minimum spacing of 6 feet from any other electrode, which would include, but not be limited to, other plate or concrete­-encased electrodes.

Section 250.66(A) requires a minimum six AWG copper to the plate electrodes, which are commonly used where there is rocky soil and it may be difficult to drive a rod eight feet completely into the earth. 

Plate electrodes expose more surface area to the soil and may result in a lower resistance to earth. It is likely that this venue has a need for a lower ground resistance, and the engineer is using electrodes with as much surface area as possible. Plate electrodes are readily available in steel and nonferrous metals.

TC cable

The generator manufacturer supplied Type TC-ER cable that contains power and control conductors for a commercial/retail occupancy. The cable enters above the ceiling in the basement and travels a short distance above a lay-in ceiling into a panelboard. The inspector failed this installation, and we were required to install another wiring method. Is that correct?

The inspector is correct. Residential installers have become familiar with installing Type TC-ER cable in dwelling units for generator installations as permitted in 336.10 list item (9). It is important to note that this permissive language is limited to one- and two-family dwelling units. See Section 336.12, which addresses uses not permitted for TC cable.

Specifically, see 336.12 list item (2) that prohibits TC cable from being installed outside a raceway or cable tray system, except as permitted in list items; in 336.10(4) for outdoor installations supported by a messenger wire; 336.10(7) between a cable tray and utilization equipment; 336.10(9) in one- and two-family dwelling units where the cable contains power and control conductors (typically a generator installation); and 336.10(10) where direct buried. Permanently connected appliances, such as a point-of-use indoor electric water heater,  rated over 300 VA are permitted to use the branch circuit overcurrent device (circuit breaker or fused disconnect) as the disconnecting means where it is within sight from the appliance or is capable of being locked in the open position in compliance with Section 110.25. A fused disconnect will typically have a means to lock it in the open position and accessory devices for circuit breakers are readily available. They are typically placed over the circuit breaker and must remain in place with or without the lock installed. 

Fire pump transfer switch location

In an effort to save the owner some money, can we locate the fire pump transfer switch in the electrical equipment room? There we can tap ahead of the building service disconnect for the normal supply to the transfer switch and take just one set of conductors to the fire pump controller. Is that Code compliant?

No, see 695.3(F), which requires the transfer of power to the fire pump controller between the individual source and the alternate source to take place within the fire pump room. The NEC does not have purview over the performance of the fire pump. 

This requirement is extracted from NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection. A fire, or other incident such as damage at the transfer switch in the electrical room, would remove both power sources from the fire pump controller. This requirement mandates that the individual and alternate sources enter the fire pump room independently and the transfer of power takes place in that location.

Disconnect required?

Does a 4,000W, 277V point-of-use indoor electric water heater require a disconnecting means installed at the heater’s location?

The general requirement in Part III of Article 422 for appliances mandates a disconnecting means to simultaneously disconnect all appliances from ungrounded conductors. 

Sleeve NM cable in conduit?

We are replacing house panels in an occupancy of Type III construction with existing Type NM cable. There is a 24-inch piece of 2-inch EMT out of the top of these panelboards with Type NM cable sleeved through the conduit into the panelboard. Is that permitted?

The general rule in Section 312.5(C) (for cabinets containing panelboards) is that each cable be secured to the cabinet in which the panelboard is installed. However, Exception No. 1 does permit cables with entirely nonmetallic sheaths to be installed through a nonflexible raceway not shorter than 18 inches and not longer than 10 feet. 

There are seven list items addressing additional requirements that must be met to exercise this exception. Each cable must be fastened within 12 inches of where it leaves the raceway, which must extend directly above the enclosure but cannot penetrate a structural ceiling. 

Fittings must be provided on the raceway to protect the cables, and the raceway must be plugged or sealed to prevent debris from entering the panelboard. The cable sheath must extend through the raceway and into the enclosure not less than ¼ inch, and the cable fill must be calculated in accordance with Table 1 of Chapter 9. 

Where conduit or tubing nipples do not exceed 24 inches, Note 4 to Table 1 permits fill up to 60% and the ampacity adjustment factors in 310.15(C)(1)(b) for more than three current-carrying conductors do not apply. Due to the elliptical shape of Type NM cable, when calculating 60% fill, the cross-sectional area calculation must be based on using the major diameter of the ellipse as a circle diameter.

About The Author

DOLLARD is retired safety coordinator for IBEW Local 98 in Philadelphia. He is a past member of the NEC Correlating Committee, CMP-10, CMP-13, CMP-15, NFPA 90A/B and NFPA 855. Jim continues to serve on NFPA 70E and as a UL Electrical Council member. Reach him at [email protected].






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