Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Send questions to firstname.lastname@example.org. Answers are based on the 2017 NEC.
Ungrounded delta system
Is ground-fault protection of equipment (GFPE) required for a 480-volt (V), three-phase, ungrounded delta system that is supplying an industrial furnace?
No. Your question does not explain the type of conductors as described in the NEC supplying the furnace or the size of the disconnecting means involved. Requirements for GFPE in the NEC are located in 210.13 for branch circuits, in 215.10 for feeders and in 230.95 for services. The text in each of these requirements specifically refers only to solidly grounded wye connected electrical systems of more than 150V to ground but not exceeding 1,000V phase to phase. GFPE is required in each section for disconnecting means rated at 1,000 amperes (A) or more. These GFPE requirements are meant for 480/277V wye-connected systems which lend themselves very well to sustained arcing events where one occurs. Note that ground fault detection is required.
See Section 250.21, which permits a 480V ungrounded system to supply an industrial electric furnace. This requirement then mandates ground detectors in 250.21(B) for ungrounded systems operating at not less than 120V and at 1,000V or less. The ground detection equipment is required be located as close as possible to the source. Additionally, the source or the first disconnecting means of the ungrounded system must be marked “Caution: Ungrounded System Operating at 480 Volts Between Conductors.”
Indoor dedicated equipment space
Electrical rooms in commercial facilities get overcrowded very quickly. There is barely enough room for the number of panelboards, transformers and so on that we need to install. We are having a bit of a debate with respect to dedicated equipment space. Is it permissible for a conduit leaving a panelboard to enter (pass through) the equipment space above another panelboard in order to leave the room?
The NEC requirement you are referring to is 110.26(E), Dedicated Equipment Space. For indoor locations, the dedicated equipment space is equal to the width and depth of the equipment extending from the floor to a height of 6 feet above the equipment or to the structural ceiling, whichever is lower. See 110.26(E)(1)(a), which prohibits piping, ducts, leak protection apparatus, or other equipment foreign to the electrical installation from being located in this zone. This requirement is directed at foreign equipment, which would include but not be limited to plumbing, ductwork and systems other than electrical. A conduit or cable assembly from one panelboard or other piece of electrical equipment would not be considered as foreign to the electrical installation and is permitted to pass through the dedicated equipment space.
Conductor sizing, capacitor at motor
When installing a capacitor at the motor, how do I determine the minimum size conductor? Is it rated on the capacitor, the motor, the overload protection or the branch-circuit short-circuit ground-fault protection?
Where a capacitor is connected directly to the terminals of a motor or to the motor circuit conductors, Section 460.8(A) requires it be sized at a minimum of one-third the capacity of the motor circuit conductors and not less than 135 percent of the rated current of the capacitor installed at the motor. In this type of installation, the capacitor is installed on the load side of a motor overload protective device and a separate overcurrent protective device is not required to protect the capacitor.
COPS risk assessment
Where a critical operations power system (COPS) is installed, is it the responsibility of the contractor to do a risk assessment as required in 708.4? What would be considered in the risk assessment?
The NEC requires a risk assessment be performed to identify hazards, the likelihood of their occurrence and the vulnerability of the electrical system to those hazards. COPS are installed in vital infrastructure facilities that, if destroyed or incapacitated, would disrupt national security, the economy, public health or safety and where enhanced electrical infrastructure for continuity of operation has been deemed necessary by governmental authority. The hazards considered include, but are not limited to, naturally occurring hazards, geological, meteorological and biological. Hazards also include human caused events both accidental and intentional.
There are multiple references and extract material in Article 708 to NFPA 1600, Standard on Disaster/Emergency Management and Business Continuity Programs. This standard provides guidance concerning risk assessment and identification of hazards. The risk assessment must be performed using NFPA 1600, which prescriptively lists all types of geological, meteorological, biological, accidental human caused, intentional human caused and technological hazards. In my opinion, the average electrical contractor may not have the expertise, experience and capability to perform this type of risk assessment and may need to consult with a subject matter expert.
Sign colors in the NEC
We made our own signs using text as required by the NEC for multiple signs on a recent job. We were questioned on the use of the sign colors by the customer’s safety director. As the cost was insignificant, we just replaced the signs. Does the NEC mandate the color red be used on a danger sign?
The requirement that you are referring to is found in 110.21, Marking, and specifically in 110.26(B) for field applied hazard markings. The NEC requires that caution, warning or danger signs be marked to warn of the hazards using effective words, colors, symbols or any combination. Additionally, the signs or labels must be permanently affixed to the equipment or wiring method and must be durable to withstand the environment in which they are installed.
The NEC does not prescriptively address colors and font sizes, etc. There are multiple informational notes that reference other standards which provide guidelines for suitable font sizes, words, colors, symbols and locations. The safety director was right to question the colors and font sizes used in the field-made signs and labels. Federal regulations require the prescriptive use of colors and font sizes, etc., where caution, warning and danger signs are required. See the requirements for these signs and labels in the construction standard, Section 1926.200 and in the general industry standard 1910.145. While these requirements located in OSHA regulations cannot be enforced by the electrical inspector, they do have a significant impact on all installer/maintainers.
Circuit breaker rating/setting
What is the difference between a circuit breaker rating and a circuit breaker setting?
A circuit breaker is designed to open and close a circuit by both non-automatic (manually) and automatic means. A circuit breaker opens on a predetermined overcurrent without causing damage to itself when it is properly applied within its rating. Adjustable-type circuit breakers can be set to trip at various values of current and time. A circuit breaker setting is the value of current and time or both of which an adjustable circuit breaker is set to trip.
For example, an 800A electronic trip molded case circuit breaker has a rating of 800A. It may be adjusted to a long time pick up of 750A. Therefore, the 800A rated circuit breaker has a setting of 750A. See the definition of circuit breaker in Article 100.
In a commercial building used as offices, we have with two services. There is a 600A, 208V service-supplied panelboard with a 600A circuit breaker main as the service disconnect. There is a second service-supplied 400A main lug only panelboard that contains six disconnects (circuit breakers) for heating throughout the building. The panelboard with six disconnects for the heat was installed to obtain a cheaper rate from the utility. This results in a total of seven service disconnects for this building. Is that a Code violation?
Section 230.71(A) permits up to six disconnects in the single enclosure that you have described. This requirement specifically permits this for each service permitted by Section 230.2. An additional service for different voltages, frequencies, or phases, or for different uses—such as for different rate schedules—is permitted in 230.2(D). The installation that you have described is not a violation of the NEC .
It is interesting to note that the first draft for the 2020 NEC has modified 230.71 to prohibit six service disconnects in a single enclosure. Six disconnects are still permitted but they must be in separate enclosures or compartments. Substantiation to support the proposed revision explained that there was no way to determine adequate personal protective equipment to protect installer/maintainers that may need to work in such service equipment. Where a single main overcurrent protective device is installed as a service disconnect in a panelboard, the bus can be de-energized, which significantly reduces the likelihood of an incident.
Junction box access
Where limited space is available, is it permitted to install a junction box behind a photovoltaic (PV) panel? In this case, the panel can be removed for access by removing the listed clips that secure it to a rack.
Yes, a junction box is permitted behind the PV module or panel provided the junction box is installed so that the wiring can be rendered accessible by removing a module or panel that is secured by removable fasteners and connected to a flexible wiring system. See Section 690.34.