Objectionable Current, New NEC Requirements and Existing Installations and More

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Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code, Jim will help you solve it. Send questions to codefaqs@gmail.com. Answers are based on the 2017 NEC .

Objectionable current

We are installing racks to contain audiovisual equipment that will be used to edit films. The owner is concerned about electrical noise and the impact on the audiovisual equipment. There is a significant amount of additional grounding installed in this building, including a ground ring, chemical ground rods and the bonding of each vertical steel column. The audiovisual equipment racks will each be supplied with six 120-volt (V) circuits for receptacle outlets. The owner has requested that we do not terminate equipment-grounding conductors (EGCs) on the receptacles supplying the equipment in attempt to eliminate electrical noise. The racks will be bonded to the vertical steel columns for the fault return path. Can we consider the EGC connection as objectionable as seen in 250.6 because we are concerned about interference?

No. Section 250.6(B), Alterations to Stop Objectionable Current, does provide four permitted alterations to stop objectionable current provided that the requirements of 250.4(A)(5) or (B)(4) are met. Section 250.4 provides general requirements for grounding and bonding and (A) addresses grounded systems. An effective ground-fault current path is required by 250.4(A)(5). This requires electrical equipment and other conductive material that are likely to become energized to be installed in a manner that creates a low-impedance ground-fault current path to facilitate the operation of an overcurrent-protective device. This ground-fault current path must be capable of safely carrying the maximum ground-fault current. Relying on a bonding conductor to a vertical steel column does not result in an effective ground-fault current path. Section 300.3(B) requires that all conductors of the same circuit, including the grounding conductor, all EGCs and bonding conductors be installed in the same raceway, cable, etc. There is no relief in 300.3(B)(1) through (4), in this case.

New NEC requirements and existing installations

Our area is now subject to the requirements of the 2017 NEC. Requirements for overcurrent protective devices (OCPDs) supplying marinas in Article 555 were changed from the 2014 NEC to now require ground-fault protection (GFP) that does not exceed 30 milliamperes (mA). Since there are no requirements for replacements, how do I handle a circuit-breaker replacement for shore power? Isn’t this similar to a service upgrade and AFCI requirements where we are not required to install an AFCI CB? Is a replacement CB supplying shore power required to have GFP?

The NEC is not retroactive, meaning that an existing installation is not generally required to be upgraded when a newer edition of the NEC modifies an existing requirement. For example, a marina installed in 2001 is not required to upgrade to 30 mA GFP for all shore power to comply with the 2017 NEC. Some local jurisdictions may exempt replacements of a circuit breaker from any Code requirement or the need for an inspection. It is important to note that some jurisdictions are implementing legislation to upgrade electrical systems in marinas due to electric-shock drownings (ESD) that occurred in their jurisdiction. For example, look at local requirements in Kentucky, Tennessee and West Virginia. In many cases, the real question is: “will replacement of devices trigger or require an electrical inspection?”. If an ESD occurs, there will likely be a third-party civil suit.

Modifications to existing electrical systems and equipment are, in general, required to be in compliance with the edition of the NEC in effect at the time the replacement occurs. This question references the requirements of 210.12(D) as an example to illustrate that replacement CBs in a marina would not have to provide GFP. This requirement is based solely on extensions or modifications to the branch circuit and not the upstream OCPD. Section 210.12 does not require the replacement of an existing CB be upgraded to an AFCI CB. Section 210.12(D) exists to provide that clarity. Without the requirements in 210.12(D), an electrical inspector could require all dwelling-unit service upgrades to include AFCI protection as required in 210.12(A). It is extremely important to note that there is no such requirement in Article 555. The requirements in the introduction of the NEC are clear: 90.2(A) indicates that the NEC covers “ … the installation and removal of electrical conductors, equipment …” and 555.1 Scope clarifies that Article 555 covers “… the installation of wiring and equipment in the areas … .” The removal and replacement of CBs supplying shore power must comply with the NEC that is currently adopted.

Through a tentative interim amendment (TIA), Article 555 now requires feeders, branch circuits and receptacles be provided with GFP not exceeding 30 mA. It is very important to note that 555.3 has been modified by TIA 17-15 significantly expanding GFP requirements. The TIA adds two new definitions for docking facility and marina. Additionally, the TIA significantly modified Section 555.3 to require GFP in accordance with 555.3(A) and (B) for all docking facilities other than floating buildings covered in Article 553. GFP is required for all branch circuits and feeders for currents exceeding 30 mA. Additional text permits the feeder OCPD to be coordinated with downstream GFP. Section 555.3(B) requires all receptacles providing shore power to be provided with GFP not exceeding 30 mA in lieu of the GFCI requirements in 210.8.

This is a question that you should also ask the local authority having jurisdiction and the electrical inspector.

Vertical support of conductors

Where are the NEC requirements for supporting high-voltage feeders in vertical raceways? Part II of Article 300 contains requirements for more than 1,000V, but there is no section for vertical support.

Section 300.19, Supporting Conductors in Vertical Raceways, applies to all voltages. Article 300, General Requirements for Wiring Methods and Materials, is logically separated in two parts. Part I is for general requirements and Part II is for requirements for over 1,000V, nominal. The requirements in Part I are general in nature and apply to all systems, including those rated below and over 1,000V. The requirements of Section 300.19 are not based on the conductor’s voltage. Applying this requirement involves identifying the type of conductor as (1) copper, or (2) aluminum or copper-clad aluminum and the conductor size. Due to the difference in the weight of the material, copper conductors must be supported at shorter intervals. Where necessary in Part I, a reference to installations below and over 1,000V is included as seen in 300.2(A) and 300.3(C). Part II contains requirements that apply only where the voltage is over 1,000V, nominal.

Concrete-encased electrode connection

Are connections from the grounding electrode conductor to the concrete-encased electrode required to be accessible? We have an inspector that wants us to have the contractor pouring the grade beams to leave a piece of rebar sticking up through the grade beam so that he can see where we make our connection. Is that a Code requirement?

No, that method is permitted in 250.68(C)(3) but is not required. A rebar-type concrete-encased electrode installed in accordance with 250.52(A)(3) with an additional rebar section extended from its location within the concrete to an accessible location that is not subject to corrosion is permitted (not required) for connection of grounding electrode conductors and bonding jumpers. Where a rebar leaves a grade beam (in contact with the earth), there is a possibility of corrosion. The general rule in 250.68(A) requires all mechanical elements used to terminate a grounding electrode conductor or bonding jumper be accessible. Section 250.68(A) Exception No. 1 permits an encased or buried connection to a concrete-encased, driven, or buried grounding electrode to not be accessible.

Termination of stranded conductor

Is it permitted to separate the strands of a grounding conductor and land them under two screws in a terminal bar? We had a 3/0 AWG grounding electrode conductor specified for a smaller system and the terminal bar would not accept a 3/0 copper. We installed a separate lug.

No, that would be a violation of Section 110.3(B). Terminal bars and lugs will be marked with the minimum and maximum size conductors permitted.

Panelboards in damp or wet locations

In unfinished basements, we have always mounted panelboards on backboards, unistrut or other material to prevent the metal from being in contact with the block or concrete due to potential moisture problems. When questioned by the company owner, I could not locate a Code requirement to support my installation method. Is it required to keep the panelboard off of a masonry surface in contact with the earth?

You are correct, the NEC requires a minimum airspace. Panelboards are defined in Article 100 as being designed to be placed in a cabinet or cutout box placed in or against a wall, partition or other support and accessible only from the front. Cabinets are covered in Article 312, Cabinets, Cutout Boxes, and Meter Socket Enclosures. Section 312.2, Damp and Wet Locations, requires surface-mounted cabinets in damp or wet locations be placed or equipped so as to prevent moisture or water from entering and accumulating within the cabinet and the cabinet must be mounted so there is at least ¼-in. airspace between the cabinet and the wall or other supporting surface. There is an exception for nonmetallic enclosures which are permitted to be installed without the airspace on a concrete, masonry, tile or similar surface.

About the Author

Jim Dollard

Code Columnist

Jim Dollard is the safety coordinator for IBEW Local 98 in Philadelphia. He is a member of the NEC Correlating Committee, NEC CMP-10, NEC CMP-13, NFPA 70E, NFPA 90A/B and the UL Electrical Council. He can be reached at codefaqs@gmail.com.

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