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.

Manufacturer instructions vs. NEC

What do I do when product manufacturer instructions conflict with requirements in the NEC? Many high-end refrigerators and small water heaters trip GFCI devices regularly. The appliance manufacturer’s instructions always state that GFCI protection should not be provided, but the NEC requires it. Can you help?

The GFCI requirements in the NEC must be met. The equipment identified in your question meets the definition of an appliance in Article 100. Appliances are built to product standards, which mandate limits to leakage current at values that will not trip a GFCI. It is for this reason that Section 422.6 requires all appliances supplied at 50V or higher to be listed. Where a new appliance is tripping a GFCI, it is recommended that you contact the appliance manufacturer and the listing agency. In most cases, the manufacturer does not prohibit GFCI protection of an appliance in their instructions, they simply recommend it not be installed.

Appliance receptacle location

A general contractor takes exception to us drilling through a cabinet side wall to plug in the permanently mounted dishwasher. He claims cords cannot go through holes and prefers the receptacle behind the dishwasher like a refrigerator receptacle being behind the unit. Is the receptacle permitted behind the dishwasher? 

The NEC does not provide prescriptive requirements for the location of a receptacle outlet supplying a refrigerator. They are typically installed behind the appliance that is easily rolled out if needed. There is no prohibition in the NEC to drilling a hole in a cabinet wall to supply an appliance, such as a dishwasher, from a receptacle outlet in an adjacent cabinet space. The NEC does prohibit running a cord through holes in walls, structural ceilings, suspended ceilings, dropped ceilings or floors. See Section 400.12. Article 422 contains requirements for appliances and Section 422.16 addresses flexible cords. Requirements for specific appliances in 422.16(B) include the permitted cord lengths and location of the receptacle outlet. The receptacle for a built-in dishwasher (422.16(B)(2)) must be in the space adjacent to the space occupied by the dishwasher. Where a flexible cord passes through an opening in a cabinet wall, it must be protected from damage. A bushing, grommet, smoothed edge or other approved means of protection is required.

Disconnect required?

We installed a 200A, 208/120V feeder into an MLO panelboard to a new garage at a car dealership. The new garage is 60 feet from the dealership. However, there is an overhead awning to protect from the weather as you walk between buildings, and there is a single owner, making it one building. We complied with 408.36, but the inspector failed us and required a main disconnect in the garage. Is the inspector correct?

Yes, the inspector is correct. In this installation Article 225 applies because there is an “outside feeder” installed. Our format here is questions and answers dealing with NEC compliance, not building codes. The defined term “building” in Article 100 and the local building codes will dictate where more than one building exists. In general, to qualify as a single building there is typically a physical connection that allows for sharing a functional space. This could be shared underground parking, an atrium, ground floor retail or a lobby to be considered a single building or structure. Walkways between buildings are not considered functional, shared space, even if they are lighted or heated. Additionally, the building ownership has no effect. 

The requirement you referenced in 408.36 requires all panelboards to be protected by an overcurrent protective device (OCPD) with a rating not greater than the panelboard’s. This OCPD is required to be located within the panelboard or at any point on the supply side of the panelboard. In this installation, the properly protected feeder leaves the building to supply another building. It is an outside feeder and must comply with 225.31, requiring a disconnecting means. Section 225.31(B) requires this disconnecting means to be installed either inside or outside of the building or structure served or where the conductors may pass through the building or structure. In all cases, the disconnect must be readily accessible and installed nearest the point of entrance of the conductors.

Bollards to protect EV chargers

During plan review, the township noted that bollards are required for each outdoor electric vehicle fast charger location in a retail parking lot. Is that a Code thing?

There is a general requirement in Section 110.27(B) that mandates enclosures or guards where electrical equipment is likely to be exposed to physical damage. Each installation is different and must be considered on a case-by-case basis. Protecting electrical equipment or wiring methods from physical damage is a determination that must be made by the installer and inspector. In many cases, concrete curbs can provide the necessary protection.

Minimum operating temperature

Drawings for a new cold storage facility require conductor insulation types rated for the temperature in each area. Is Type THWN-2 insulation rated for use in a cold storage facility that will range from -1°C to -20°C? Table 310.4(1) provides maximum operating temperatures, but not minimum.

See the informational note following Section 310.4, which states that thermoplastic insulation may stiffen at temperatures lower than -10°C (14°F). It is important to note that this is not a requirement; it is informational only. Thermoplastic insulation is not prohibited, but there may be an insulation type with properties better suited to extreme cold. For example, an internet search revealed industry recommendations for minimum temperatures at -10°C for thermoplastic insulation such as THWN-2, and -40°C for thermoset insulation such as XHHW-2.

Supplying a circuit breaker enclosure

Are we permitted to take tap conductors directly from the load side of an existing circuit breaker? This is an older industrial facility, and we need to supply equipment at 400A. There is ample capacity, but the problem is getting a 400A circuit breaker for the existing equipment. Can we take 500 kcmil copper directly from the load side of a 600A circuit breaker to supply a 400A circuit breaker enclosure?

Section 240.21(B) for feeder taps will apply in this installation. See the parent text in this section that clarifies that the tap is permitted at any point on the load side of the feeder OCPD, meaning the load side of the 600A circuit breaker in this installation. The parent text also mandates that the application of Section 240.4(B) to round up to the next larger OCPD is not permitted for tap conductors. Assuming the existing circuit breaker and new equipment supplied have a temperature limitation of 75°C, a 500-kcmil THHN copper conductor’s ampacity is rated at 380A and cannot be rounded up to 400A. A 600-kcmil copper tap conductor would be required. In older installations, it is common for circuit breakers to be rated at 60°C only, meaning we must use ampacities in the 60°C column. See Section 110.14(C). This could affect the installation significantly as 750-kcmil copper tap conductors (rated at 400A at 60°C) would be required.

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 (450.9) 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. 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.

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