NEC Questions and Answers based on 2020 NEC^® - June 2020

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For EC&M Magazine
By Mike Holt, NEC^® Consultant
Here's the follow-up to yesterday's newsletter. This includes the answers to the questions sent, so you can see how you did.

Note: The answers to these questions are based on the 2020 NEC.
Underlined text indicates a change for the 2020 NEC.

Q1. What is the NEC definition of an electric vehicle?
A1. Electric Vehicle. An on-road use automobile, bus, truck, van, neighborhood electric vehicle, or motorcycle primarily powered by an electric motor [Article 100 Definitions].

Author’s Comment:
►Plug-in hybrid type vehicles containing both an electric motor and a combustion engine that portion of which pertains to the re-charging of the electric motor is covered by Article 625.

Q2. What does the Code define as a dormitory unit?
A2. Dormitory Unit. A building, or a space in a building, in which group sleeping accommodations are provided for more than 16 persons who are not members of the same family in one room, or a series of closely associated rooms, under joint occupancy and single management, with or without meals, but without individual cooking facilities [Article 100 Definitions].

Q3. What does the Code mean by available fault current?
A3. Fault Current, Available (Available Fault Current). The largest amount of current capable of being delivered at a point on the system during a short-circuit condition [Article 100 Definitions].

Informational Note: A short circuit can occur during abnormal conditions such as a fault between circuit conductors or a ground fault. (See Informational Note Figure 100.1 in the NEC.)

Author’s Comment:
Fault current is current outside the usual circuit path and with a magnitude that exceeds the normal circuit current. A fault can be line-to-line, line-to-neutral, or line-to-ground. The new NEC Informational Note, Figure 100.1, helps explain the differences between “Available Fault Current,” “Short-Circuit Current Rating” (SCCR), and “Interrupting Rating” (AIC). The available fault current is the largest amount of current available at that point on the circuit. It is important to note that the fault current value is not the same throughout the circuit; it becomes smaller as the impedance is increased between the point of the fault and the source of the power.
►The SCCR is the maximum amount of current that equipment, other than overcurrent protective devices (OCPDs), can safely withstand. Much of the equipment supplied by the electrical system is required to be marked with this rating. The designer and installer need to make sure the fault current available at the equipment is less than what the equipment can withstand. This often needs to be addressed at the design stage of a project so specified equipment can have a suitable SCCR. Correcting an installation where the available fault current exceeds the SCCR of the equipment after it has been installed can be costly and time consuming. One very common issue is with large air conditioning equipment which often has an SCCR of 5,000A, unless a higher rating was specified at the time the equipment was purchased.
►The interrupting rating of an overcurrent protective device is the maximum amount of current that an OCPD can safely interrupt. OCPDs that are subjected to currents exceeding their AIC (or KAIC) rating may fail violently. Applying equipment within their SCCR or AIC ratings is critical for a safe installation.

Q4. How is a habitable room is defined in the Code?
A4. Habitable Room. A room in a building for living, sleeping, eating, or cooking, but excluding bathrooms, toilet rooms, closets, hallways, storage or utility spaces, and similar areas [Article 100 Definitions].Figure 01

Q5. What is the Code rule for access to and egress from working space of large equipment that contains overcurrent devices?
A5. Access to and Egress from Working Space [110.26(C)]

(1) Minimum Required. At least one entrance of sufficient area must provide access to and egress from the working space.

Author’s Comment:
►Check to see what the authority having jurisdiction considers “sufficient area.” Building codes contain minimum dimensions for doors and openings for personnel travel.

(2) Large Equipment. For large equipment that contains overcurrent devices, switching devices, or control devices, an entrance to and egress from the required working space not less than 24 in. wide and 6½ ft high is required at each end of the working space. This requirement applies for either of the following conditions:

(1) Where equipment is over 6 ft wide rated 1,200A or more

(2) Where the service disconnect is over 6 ft wide and where the combined ampere rating is 1,200A

Open equipment doors must not impede the entry to or egress from the working space.

A single entrance for access to, and egress from, the required working space is permitted where either of the following conditions are met:

(a) Unobstructed Egress. Where the location permits a continuous and unobstructed way of egress travel.

(b) Double Working Space. Where the required working space depth is doubled, and the equipment is located so the edge of the entrance is no closer than the required working space distance.

Author’s Comment:
►The requirement for a path of egress with the door open may require wider aisle space. The Code does not give specific guidance as to the required width of the egress path, but the egress door must be at least 24 in. wide. It would be reasonable to ensure the aisle has a width equal to the door plus 24 in. Doors that open more than 90 degrees would be ideal for providing more space for egress.

(3) Fire Exit Hardware on Personnel Doors. Where equipment rated 800A or more that contains overcurrent devices, switching devices, or control devices is installed and there is a personnel door(s) intended for entrance to and egress from the working space less than 25 ft from the nearest edge of the working space, the door(s) are required to open in the direction of egress and be equipped with listed panic or listed fire exit hardware on personnel door(s) for entrance to, and egress from, the working space. Such doors must open in the direction of egress. 

Author’s Comment:
►History has shown that electricians who suffer burns on their hands in electrical arc flash or arc blast events often cannot open doors equipped with knobs that must be turned or those that must be pulled open.
►Since this requirement is in the NEC, the electrical contractor is responsible for ensuring that panic hardware is installed where required. Some are offended at being held liable for nonelectrical responsibilities, but this rule is designed to save the lives of electricians. For this and other reasons, many construction professionals routinely hold “pre-construction” or “pre-con” meetings to review potential opportunities for miscommunication—before the work begins.
►The minimum requirement to provide listed panic hardware at or above 800A shouldn’t overshadow the importance to perform a risk assessment to incorporate specific room design, equipment layout, and egress accessibility