Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at email@example.com. Answers are based on the 2020 NEC.
Does the NEC require bollards to be installed to protect electrical equipment outside a building?
The general requirement in the NEC is that electrical equipment likely to be exposed to physical damage must be protected by guarding or enclosing it in a manner sufficient to prevent such damage. See 110.27(B). This requirement does not specifically identify any type of protection and is left up to the installer and the authority having jurisdiction. The first step is to consider the likelihood of physical damage. Where is the equipment located, and what type of activity will occur in the area that could affect the equipment? For example, a pad-mounted transformer (450.8(A) and 110.27(B)) and other equipment in a parking lot would be subject to physical damage if a vehicle were to drive into the equipment, so steps must be taken to protect it, such as putting fencing around the installation or installing bollards. The requirement to protect equipment from physical damage is not limited to outdoor installations.
How far from a wall must a dry-type transformer be installed to allow for proper ventilation?
Section 450.9 contains requirements for transformer ventilation. Transformers must be installed so they can dissipate full load heat losses without a temperature rise in excess of the transformer rating.
All openings in the transformer enclosure for ventilation must be kept clear of any airflow obstructions. The NEC also mandates that manufacturers mark the required clearances for ventilation on the transformer, and installers must label the top of transformers that are horizontal and readily accessible to warn people not to store material on top of them, which will act as insulation and limit the ability to dissipate heat.
CCCs in wireways
When there are more than 30 current-carrying conductors (CCCs) in one spot in a wireway, can we use the 10-foot rule for ampacity? An inspector forced us to reroute branch circuits so there were not more than 30 CCCs in one spot. Is that correct?
Yes, the inspector is correct. Metal wireways are covered in Article 376, and specific requirements in the article modify the general rules for conductor ampacity. Permitted ampacity and number of conductors for wireways is addressed in 376.22. The number of conductors and cables in a wireway must not exceed 20% of the cross-sectional area of the wireway. The general rule in Section 310.15(C)(1) requires that the ampacity of each CCC be reduced where the number of CCCs in a raceway exceeds three. However, the permissive requirements of 376.22(B) modify the general rule and permit up to 30 CCCs at any cross-section in the wireway before the adjustment factors of 310.15(C)(1) must be applied. Significant relief is already provided. This permissive text allows 10 times the number of CCCs without any length limitation.
The 10-foot requirement you refer to is located in 310.14(A)(2) for selection of ampacity. In general, this requires that for a circuit in which two ampacity values exist, the lowest value must be used. The exception to this general rule permits the higher ampacity value to be used if the total portion of the circuit with the lower ampacity does not exceed the lesser of 10 feet or 10% of the total circuit length.
Application of the permissive exception applies, for example, where a feeder must pass through an area with a higher ambient temperature requiring a reduction in ampacity in accordance with 310.15(B)(1) for the portion of the circuit with higher ambient temperature. This exception does not apply to wireways, nor in 310.15(C)(1)(b), which exempts the need to derate for the number of CCCs installed in raceways having a length not exceeding 24 inches. If the technical committee with purview over conductor ampacity were to agree that the exception following 310.14(A)(2) supersedes the requirement in 376.22(B), the same committee would have to modify 310.15(C)(1)(b). That would allow raceways of a length not exceeding 10 feet to have an unlimited number of CCCs in all cases. While there may be a need for additional clarity in the application of the exception following 310.14(A)(2), the existing rules are clear. Where the number of CCCs at any cross-sectional area of a wireway exceeds 30, the adjustment factors in 310.15(C) apply. Installers can easily avoid these issues with proper planning.
It is interesting to note that multiple public inputs were made to modify 376.22(B) to permit the application of exception following 310.14(A)(2) and they were all rejected.
Elevated platform installation
To conserve space, a designer has 5-kV service equipment and a 5-kV switchgear lineup installed on an elevated platform. Is the service equipment and distribution equipment for an industrial installation permitted to be installed on an elevated platform?
The NEC specifically permits electrical equipment rated at over 1,000V to be installed on a platform, provided that all other applicable NEC requirements are met. Section 110.33(B) requires permanent ladders or stairways be provided to give safe access to the working space around electrical equipment installed on platforms, balconies, etc. Note that all other pertinent requirements will apply including, but not limited to, sections 110.31, 110.32, 110.33, 110.34 and 230.205(A).
Standby generator labeling
Where is the labeling of a standby generator location required? Can it be placed at the metering location?
Standby generators can be used in multiple systems, including emergency, legally required and optional standby systems. Three Chapter 7 articles address signage requirements indicating the type and location of standby power sources. Emergency and legally required systems (700.7(A) and 701.7(A)) require a sign at the service entrance equipment identifying the type and location for each emergency and legally required standby power source. Signage noting the type and location of optional standby power sources (702.7(A)) installed in commercial and industrial locations must be installed at the service entrance equipment.
Optional standby sources installed in one- and two-family dwelling units (typically a standby generator) must be identified at the emergency disconnecting means required in 230.85. This sign must identify the location of each permanently installed optional standby disconnecting means or the means to shut down the prime mover. Note that where the sign is required to be located at the “service equipment,” is the location of the service disconnecting means and not the meter/metering location. See the Article 100 definition of service equipment. The requirement for signage for optional standby systems for one- and two-family dwelling units is required at the location of the emergency disconnecting means required in 230.85, which may or may not be the service disconnecting means.
Reconditioned circuit breakers
With all the supply-chain shortages, some circuit breakers are difficult or impossible to get. Can we use reconditioned or used molded-case and low-voltage power circuit breakers (LVPCB)?
Section 240.88 addresses circuit breakers and reconditioning. Molded-case circuit breakers are not permitted to be reconditioned. However, LVPCBs and medium/high-voltage power circuit breakers are permitted to be reconditioned. Electronic trip units for LVPCBs are not permitted to be reconditioned. Used circuit breakers are permitted. It is vital to understand and apply the Article 100 definition of reconditioned. “Reconditioned” means that the device (circuit breaker in this case) was not functioning properly and had to be restored to operating conditions. LVPCBs require maintenance at regular intervals. Typical maintenance of an LVPCB does not mean it is reconditioned; it has been properly maintained.