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. Questions can be sent to [email protected]. Answers are based on the 2014 NEC.


Electrical systems expansion


On new tenant space expansion drawings, there are 12 panelboards to install. While reviewing the panel schedules, it is apparent there is not room for additional branch circuits because almost every circuit on every panelboard is used. I have always thought the NEC required new electrical systems to include provisions for some expansion, but I cannot find anything. Can you help?


The NEC provides minimum installation requirements and does not mandate that an installation allow for expansion. The purpose of the NEC, provided in section 90.1(A), is to practically safeguard people and property from hazards that may arise from the use of electricity. Only requirements that are considered necessary for safety are included in the NEC. 


Compliance with NEC requirements will result in installations that are free from hazard but not necessarily efficient, convenient or adequate for good service or future electrical system expansion. An informational note is provided to explain that, where a system does not include some ability to expand, the system and circuits may become overloaded, creating electrical hazards. Providing the ability for future expansion is a design issue, not an NEC requirement. 


Physical damage?


When installing grounding electrode conductors (GECs) in our area, electrical contractors typically install all exposed portions of the GEC in raceways to pass the electrical inspection. This includes short sections in dwelling units to the underground water pipe and ground rods. Without a definition, it is difficult to argue that there is no potential for damage. Inspectors in my area do a really good job enforcing the NEC requirements, but, in my opinion, they go overboard where they enforce a requirement that deals with potential exposure to physical damage. How does one determine the potential for physical damage? How about severe physical damage?


The GEC serves a significant function in electrical systems and must be installed in a manner that ensures it is not damaged. GECs must be secured and protected from potential physical damage, as Section 250.64(B) states. These requirements apply to all exposed GECs and the raceway that may be used to protect them. It is not necessary to provide physical protection with a raceway in all cases where a GEC is exposed. Section 250.64(B) contains requirements for GECs sized 4 AWG and larger and for GECs that are 6 AWG in size. 


Where the NEC bases a requirement on exposure to physical damage, the installer must determine the likelihood of physical damage in each installation. This determination would include the space; the anticipated use of the space; the location of affected conductors, wiring methods or equipment; and potential activities that could cause physical damage.


There have been multiple attempts to define physical damage in the National Electrical Code. However, all have failed because it is almost impossible to capture every potential scenario in a single definition. 


I offer my opinion of physical damage and severe physical damage in the form of an example: Consider the installation of electrical systems and equipment in a new shopping center with an adjacent parking garage. An individual with a loaded shopping cart is capable of delivering physical damage if the cart were to impact wiring methods. When the individual gets into his or her car to leave the parking garage, he or she is capable of delivering severe physical damage.


Ground-fault protection


Why do the requirements for ground-fault protection of equipment (GFPE) in sections 230.95 and 215.10 apply only to systems that are both more than 150 volts (V) to ground and not more than 600V phase-to-phase? This essentially limits application to 480/277V systems and not 208/120V systems. Why is the requirement also tied to disconnects rated at 1,000 amperes (A) and not a smaller value? I see designs regularly where two disconnects at 600 or 800A are installed for a service to beat the GFPE requirement.


GFPE requirements in the NEC are directed at larger disconnecting means in systems that are likely to sustain an arcing fault to ground. Depending on where the disconnecting means is located in the distribution system, such as at the service, a 1,000A disconnect may be capable of supplying large amounts of available fault current in a ground-fault scenario. As a result, the 1,000A parameter was chosen. Depending on the system, a disconnecting means of a lower ampere rating, such as 400, 600 or 800A, will be capable of supplying a sustained arcing fault to ground as well.


We must keep in mind that the NEC provides minimum requirements, and GFPE protection at values below 1,000A is permitted. The voltage parameters focus on the 480/277V wye-connected system for good reason. These systems have a well-documented history of incidents where an arcing fault between circuit conductors and ground sustained itself resulting in the equipment’s destruction. A 208/120V system is also capable of sustaining an arc between circuit conductors and ground, depending on multiple factors including, but not limited to, the system size and the equipment involved. 


The NEC is revised every three years, and it is easy to submit your ideas and become part of the process.


Accessible overcurrent devices


In general, NEC Section 240.24 requires overcurrent protective devices to be readily accessible. The Code does not mention who should have ready access. A safety audit by the general contractor’s consultant on one of our projects pointed out we were in violation of this requirement due to doors and panelboards being locked. Who needs ready access? The NEC is not clear.


Section 240.24(A) contains a general requirement that all overcurrent devices must be readily accessible. Section 240.24(B) requires, in general, each occupant to have ready access to all overcurrent devices protecting the conductors supplying that occupancy. The occupant is not required to have ready access for service and feeder overcurrent devices where service and maintenance are provided by building management with continuous supervision. Branch-circuit overcurrent devices supplying guest rooms or guest suites without permanent provisions for cooking are permitted to be accessible only to authorized management personnel as well.


Locked doors and panelboards do not mean that overcurrent devices are not readily accessible. Section 110.26(F) permits electrical equipment rooms or enclosures housing electrical apparatus to be locked provided that qualified people have access. Where qualified people have the key to a locked electrical equipment room or panelboard, the overcurrent devices are readily accessible. Locked electrical equipment rooms, panelboards and other equipment are essential to keep unqualified people from gaining access to overcurrent devices and other electrical equipment.


Article 100 defines the term “readily accessible” and does not prohibit a lock. It reads as follows: “Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to actions such as to use tools, to climb over or remove obstacles, or to resort to portable ladders, and so forth.”


Separate building/structure GEC


Why does the NEC require all buildings supplied by feeders to have a grounding electrode or a grounding electrode system installed? The service is required to be properly grounded, and equipment grounding conductors are installed to facilitate operation of overcurrent devices in the event a fault occurs.


The answer to your question is found in Section 250.4(A)(1) and (2). Section 250.4 is extremely unusual in the NEC because it explains to the Code user the objectives of the general requirements for grounding and bonding of electrical systems. Section 250.24(A) requires a service-supplied building or structure to have a GEC connected to the grounded service conductor. This is done to “connect the system to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.” 


Section 250.32 states that a building or structure supplied by a feeder or branch circuit that originates in a service-­supplied building must also have a grounding electrode or a grounding electrode system (GES) installed. An exception in Section 250.32(A) exempts the need for a grounding electrode where only a single branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally noncurrent-carrying metal parts of equipment. A structure that is supplied by a single branch circuit will not contain a significant amount of electrical wiring and equipment.


One reason a grounding electrode or a GES must be installed in a feeder-­supplied building or structure is to limit the voltage imposed by lightning. If a grounding electrode or a GES is not installed at the feeder-supplied building, the best path to earth in the event of a lightning strike is through the feeder back to the service equipment in another building.