If you have a problem related to the National Electrical Code (NEC), are experiencing difficulty in understanding a Code requirement, or are wondering why or if such a requirement exists, ask Charlie, and he will let the Code decide. Questions can be sent to email@example.com. Answers are based on the 2011 NEC.
Ground ring understanding
NEC 250.52(A)(4) requires a ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 20 feet of bare copper conductor not smaller than 2 AWG. I suggest that, for the purposes of 250.52, it is the intent that a minimum of 20 feet of 2 AWG copper be used to develop a grounding electrode as it pertains to this section of the Code. I also submit that it is not the intent that the conductor encircle the entire building, as doing so would suggest that the larger the building, the longer the grounding electrode must be. A ground ring certainly is appropriate for absorbing the energy of a lightning strike but not as the grounding electrode as it pertains to this particular section of the Code. What say you?
It is not the intent of 250.52(A)(4) that the ground ring encircle the entire building or structure, only that at least 20 feet of conductor sized according to 250.66, but not smaller than 4 AWG, be used. The intent is that the conductor follow the contour of the building or structure and not be coiled up or concentrated in one restricted area. The Code permits a ground ring, which will function properly as the grounding electrode where installed in accordance with the requirements of 250.52(A)(4).
I think you should clarify your response to [the October 2011] reader who inquired about NEC Section 310.15(B)(5). You state that the common conductor with two-phase conductors from a 4-wire wye system is not neutral “because it is carrying the unbalanced current.” While true, the definition of a neutral in Article 100 states nothing about the need to carry only balanced or unbalanced current, only that it be connected to the neutral point of the system and be intended to carry current.
While I agree with you that the conductor is not “neutral,” some readers may be misled into thinking that the conductor is not a neutral (as per Article 100) and wonder what color that conductor should be in that case.
I hope my answer did not mislead anyone, and I believe 310.15(B)(5)(b) is quite clear regarding the “common” conductor. It would help if questions presented concerning previous Electrical
Contractor articles would identify the date of the article. I appreciate your comments and participation.
Well casing grounding
Is it required to ground the well casing at a residence if the water line is PVC?
The metal well casing is pretty well grounded by its contact with the earth. Article 100 defines “grounded” as being “connected to earth or to some conducting body that serves in place of the earth.” However, unless the metal well casing is bonded to the equipment grounding (bonding) conductor, there is no path for ground-fault current other than through the earth, which of course is a path of very high resistance and is prohibited by 250.4(A)(5) and 250.54. NEC 250.112(M) requires that, where a submersible pump is used in a metal well casing, the metal well casing shall be bonded to the equipment grounding (bonding) conductor of the circuit that supplies the submersible pump.
I am doing a restaurant kitchen that has 15- and 20-ampere (A) twistlock receptacles. Am I required, in order to provide ground-fault circuit interruptor (GFCI) protection, to install GFCI-type circuit breakers ahead of these twistlock receptacles?
NEC 210.8(B)(2) requires all 15- and 20A, 125-volt (V) receptacles installed in nondwelling-type kitchens to be GFCI--protected. This requirement covers all 15- and 20A kitchen receptacles, whether or not the receptacle serves countertop areas.
Are 15A and 20A interchangeable?
Can receptacles rated 20A be used on 15A circuits, and can 15A-rated receptacles be used on 20A circuits?
According to Table 210.21(B)(2), 20A receptacles can only be used on 20A circuits, but 15A receptacles can be used on either 15A or 20A circuits. When a 15A receptacle is used on a 20A circuit, the maximum load permitted on that receptacle is 12A. It is common practice to use 15A receptacles on 20A kitchen appliance circuits in dwelling units, but the installer should note that there are many kitchen appliances that are rated over 1,440W.
What is “redundant grounding,” and why would it be a requirement of the NEC?
The term “redundant grounding” is not used in the Code anywhere that I know of. However, Webster’s Dictionary defines redundancy as “the provision of a duplicate system or equipment as a backup.” Section 517.13(A) requires redundant grounding. Article 517 covers healthcare facilities, and because of the importance of a reliable ground-fault return path and the possibility of a failure in the metallic connections, requiring a copper-insulated grounding conductor to be run with the branch-circuit conductors ensures a reliable ground-fault return path.
I installed a two-head emergency battery lighting unit in a store. I installed the unit with one head in a hallway and mounted the second head remotely from the battery unit in a public washroom adjacent to the hallway. Is this installation in accordance with the NEC?
Emergency illumination must be installed so that a light bulb burning out will not leave the area in total darkness (see Section 700.16). That’s why units of the sort you describe are manufactured with two lighting heads. A two-lamp unit must be installed in each area you describe.
Neutral vs. ground bar
Why do we have a neutral bar and a ground bar in panels? Aren’t they the same thing? Don’t they serve the same purpose?
The neutral bar is a collection point or terminal strip for intentionally “grounded” conductors (Section 230.75). The ground bar is a collection point or terminal strip for “grounding” conductors (Section 408.40). Don’t mix conductors that serve different purposes until you are required to do so, usually at the service. Grounded conductors carry the unbalanced load of the phase conductors. Grounding conductors carry fault current. The last two statements are correct only until they reach the main service panel. At that point, when the main bonding jumper is installed (the one that grounds the neutral bar), the fault current flows from the ground bar through the metal panel frame and through the main bonding jumper to the neutral bar where it splits, and some fault current flows through the grounding-electrode conductor to the utility source. The remainder flows through the system grounded conductor back to the utility source. If, however, you were to install grounded and grounding conductors to the same grounded terminal in a subpanel, you would be establishing a parallel path for grounded conductor (neutral) current flow. That is, normal return currents would be present on both the grounded conductor and the grounding conductor, which, in some cases, could be a metal raceway. A word of caution: “Do not bond the neutral bar in other than the main service panel” [Section 250.24(A)(5)].
Exposed NM cable
Where in the Code does it say that all exposed NM cable runs below 7 feet must have raceways?
NEC 334.15(B) requires that, in exposed work, NM cable must be protected, by conduit or other means, where necessary from physical damage. This doesn’t mean it has to be installed in a complete raceway system, only that some type of protection by conduit may be used. The Code section states “where necessary,” and installation of extra protection in the garage was considered necessary by the authority having jurisdiction (AHJ). The AHJ also felt that, where the cable was installed above 7 feet, it was adequately protected.
Can the grounded (neutral) service-entrance conductor be installed as a bare copper conductor in a metal raceway?
NEC Section 230.41 Exception permits a bare copper grounded conductor to be used in a raceway or as part of a cable assembly.
Marking the high phase conductor
I’m running a circuit to a three-phase motor from a 120/240V, three-phase, delta service. Is it required to mark the high phase conductor with an orange color? Article 430 doesn’t state anything about this.
NEC 110.15 requires that the high phase conductor must be marked at each point on the system where a connection is made only if the grounded conductor is present.
TROUT answers the Code Question of the Day on the NECA-NEIS website. He can be reached at firstname.lastname@example.org.