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 2017 NEC.


Supporting Type MC cable


Are cable ties (or “Ty-Raps”) allowed for supporting Type MC cable in a ceiling? We were using metal tie-wire that comes in bundles, but we stopped when questioned by the GC.


Yes, cable ties are permitted. Section 330.30(A) provides the general requirements and permits cable ties. This requirement is modified for the 2017 NEC and mandates that cable ties be “listed and identified for securement and support.” This requirement is based on a new product standard for cable ties used in electrical installations. The new standard establishes a classification system of cable-tie-type designators. This is how the installer and inspector will determine permitted use of cable ties.


Type 2S or Type 21S cable ties are now recognized as capable of providing “securement and support” for cable assemblies and flexible conduit. The suffix “S” denotes the capability of providing “securement and support.” Where cable ties are marked as Type 1, Type 11, Type 2 or Type 21, without the “S” suffix, they may be used for other purposes, including, but not limited to, bundling, routing or grouping of cables and conductors. It is also important to note that, where cable ties are used in other spaces used for environmental air (for example, the space above a hung ceiling used for return air), they must be also listed as having low smoke and heat-release properties as required in Section 300.22(C).


Are ground rods needed?


During the plan review stage for an upcoming project, the city informed us that all of the electric vehicle (EV) chargers planned for the parking lot need to have ground rods installed. We have installed these chargers in many other areas without similar requirements. Are ground rods required for these chargers?


No. The issue and source of confusion with this application of the NEC begins with the defined term “structure.” In the 2014 NEC, this term is defined as “that which is built or constructed.” The committee that added this definition was trying to provide clarity, but, as written in the 2014 NEC, the term “structure” is extremely broad and subjective.


For example, a 4-by-4 post, a concrete pad, an EV charger, a lamp post, a canopy and any equipment installed outdoors would be considered a structure because it is all “built or constructed.” Section 250.32 contains requirements for buildings or structures supplied by feeders or branch circuits. The general rule for buildings or structures supplied by feeders or branch circuits is that a grounding electrode system (GES) be established.


However, an exception exists for installations where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment-grounding conductor. This means that the 2014 NEC required a GES for EV chargers supplied by two branch circuits. This issue has been addressed in the 2017 NEC with a revision to the defined term “structure” to clearly exclude equipment.


The new definition of structure is “that which is built or constructed other than equipment.” This is a significant improvement but will not solve this problem. Equipment typically needs some type of support or foundation. A 4-by-4 post or concrete pad does not constitute a structure; it is simply a means of support.


Night lights in receptacle plates?


A customer recently asked if I could put faceplates with built-in night lights in all of the receptacle locations in the hall and foyer areas of her home. I told her I was not aware of such a product or if the NEC would permit it. Are these available, and are they permitted?


Yes. These types of receptacle faceplate covers are available and are now recognized in the 2017 NEC. A new first level subdivision 406.6(B) permits receptacle faceplates to contain a night light or a Class 2 output (USB charger) or both, provided that they are listed and the night light or Class 2 circuitry is integral (completely inside) the faceplate cover. These devices are readily available and function with pressure devices that make contact with the exposed screw connections on the receptacle.


‘Trip-free’ circuit breakers


During a recent Code class, we got into a discussion about molded-case circuit breakers. The instructor mentioned that molded-case circuit breakers are required to be “trip free.” I put that in my notes, but I was unclear as to what it actually meant.


Section 240.80 provides requirements for the operation of circuit breakers and mandates that all circuit breakers be trip-free and capable of being closed and opened manually. The term “trip free” when applied to molded-case circuit breakers means that the contacts inside the device cannot be held closed when an abnormal condition exists. This means an accessory device that is applied to the handle of the circuit breaker to hold it in the “on” position cannot prevent the device from opening internally due to overload or short-circuit conditions.


What to identify in
emergency systems?


Recently, an inspector required us to label a standby generator and transfer switch as being part of an emergency system. It has always been a requirement to identify junction boxes so there was no mixing of normal and emergency circuits. Is it also a requirement to label the generator as well? We have never done that.


Yes. Section 700.10(A) requires all boxes and enclosures for emergency circuits to be permanently marked to readily identify them as a component of an emergency circuit or system. This includes transfer switches, generators and panelboards. It is interesting to note that this requirement has been expanded to include two additional requirements for 2017.


First, where boxes or enclosures are not encountered (typical for daisy chaining MC cable in and out of lay-in type luminaires), exposed cable or raceway systems must be permanently marked to identify it as an emergency circuit or system, at intervals not to exceed 25 feet. One method to comply would be to spray paint the cable assembly or raceway at the required interval. In addition, a new last sentence requires marking of receptacles supplied from an emergency system. This will allow the end-user to quickly identify which receptacles are supplied by the emergency system to supply equipment needed where there is a loss of normal power.


Section 90.3


I am confused as to what sections to apply when dealing with NEC chapters 5, 6 and 7. In some cases, an article contains a section to explain what else applies and what does not apply. What happens when a requirement in Chapter 5 modifies a rule in Chapter 7? What do we do?


The NEC provides requirements for how to apply the Code in Section 90.3, Code Arrangement. Revisions to this section in the 2017 NEC will help provide clarity and usability. The NEC has nine chapters; 1 through 4 apply generally. Therefore, they apply to all electrical installations. Chapters 5, 6 and 7 are special and have always supplemented or modified the requirements in chapters 1 through 4. This arrangement is revised in the 2017 NEC, and chapters 5, 6 and 7 may now supplement or modify the requirements in chapters 1 through 7. It is typical for an article in one of the special chapters to include a section that addresses “other articles.”


An example is seen in Article 760, Fire Alarm Systems. Section 760.3 explains that the only requirements of Article 300 that apply are those referenced within the article. An example of one special article modifying another special article is seen in Section 517.26. This requires the life-safety branch of the essential electrical system to meet the requirements of Article 700, except as amended by Article 517.


Perimeter pool equipotential bonding as a grounding electrode?


Can the equipotential bonding grid installed around a swimming pool be used as a grounding electrode? After all, how much do we really get from two ground rods? It is typical for us to take a feeder to a pool shed that will then supply all of the branch circuits necessary for the pool and associated area. We always install two ground rods for the grounding electrodes on all of these installations. However, in some cases, it would be beneficial to just bond to the perimeter bonding grid, if that is permitted.


No, it is not permitted. Permitted grounding electrodes are listed in Section 250.52(A). The perimeter bonding around a pool is required to bond the perimeter surface to the pool, underwater lighting, metal equipment/components, electrical equipment and fixed metal parts. The purpose is bonding only. Revisions in the 2017 NEC specifically prohibit the use of a conductive pool shell or perimeter surface bonding from being used as a grounding electrode. Section 250.52(B) now prohibits the use the structures and structural reinforcing steel described in 680.26(B)(1) and (B)(2). In addition, metal underground gas piping systems and aluminum electrodes are not permitted as a grounding electrode.


Editor’s note: For more on equipotential bonding around pool perimeters, see this month's Code Applications.