Equipotential Planes, Marking Transformers and More

By Jim Dollard | Jan 15, 2020
Electrical device. Shutterstock/ Nar Studio

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. Send questions to [email protected] Answers are based on the 2020 NEC .

Equipotential planes

Does the Code require an equipotential plane for grounding of electrical equipment controlling pumps in ponds? This installation consists of feeders that run to disconnects and control equipment for decorative fountains in multiple ponds located at a golf course. If required, how do we get this done? Is a ground ring OK?

Yes, an equipotential plane for grounding of electrical equipment is required. Article 682 contains requirements for electrical equipment installed in and around natural and artificially made bodies of water. Section 682.33 mandates equipotential planes be installed and explains that they are intended to mitigate step and touch voltages at electrical equipment. Equipotential planes are required to be installed adjacent to all outdoor service equipment or disconnecting means that control equipment in or on water, that have a metallic enclosure and controls accessible to personnel and that are likely to become energized. This will include all metal enclosures that control equipment in or on the water as they are all likely to become energized.

All of the equipment referenced in 682.33(C) and the equipotential plane must be bonded together with solid copper conductors that are insulated, covered or bare and are not smaller than 8 AWG. All connections must be made by exothermic welding or by listed pressure connectors or clamps that are labeled as being suitable for the purpose and are of stainless steel, brass, copper or copper alloy. The equipotential plane must encompass all of the walking surface around the equipment. It is required to be constructed of wire mesh or other conductive elements that are on, embedded in or placed under the walking surface and not more than 3 inches deep. The plane must extend 3 feet in all directions from the equipment where a person would be able to stand and come in contact with the equipment.

Marking transformers for storage

At a recent presentation I attended, there was discussion on marking transformers to prohibit storage. Does this apply to all transformers indoors and outdoors? Where do we apply this marking, and what should it say?

The requirement you are referencing is Section 450.9, which addresses ventilation of transformers. The general rule is to ensure that the transformer can dispose of heat and that transformers with ventilating openings be installed so that those openings are not blocked by walls or other obstructions. A new last sentence was added in the 2020 NEC in this section that requires marking to prohibit storage. It is not uncommon to see material stored on top of transformers. In fact, when work is performed in an electrical room, the top of the transformer typically becomes a workbench. Material stored on top of a transformer will act as insulation, increasing the amount of heat inside the enclosure. This new marking requirement applies only to top surfaces of transformers that are both horizontal and readily accessible. For example, a transformer in an electrical room that is readily accessible with a horizontal surface 4 feet above the floor must be marked on the top of the transformer to prohibit storage. A large transformer with a horizontal surface 6 feet above the floor would not be as readily accessible and would not require marking. This requirement does not provide specific words to include in the marking. One example would be to create labels for the top of each transformer enclosure with the words, “Do Not Store Material on This Surface.”

Habitable room

Article 210 has multiple requirements that reference “habitable rooms.” There is confusion with interpretations when referencing a habitable room. Do we just use the building code to figure this out?

The 2020 NEC now includes a definition in Article 100 of habitable room. It is a room in a building for living, sleeping, eating or cooking. The definition clearly excludes bathrooms, toilet rooms, closets, hallways, storage or utility spaces, and similar areas.

Equipment secured to grounded metal supports

Does section 250.136 permit a single equipment grounding conductor (EGC) terminated on a metal support rack to act as the EGC for all equipment mounted on the metal rack?

No, Section 250.136 does not permit the metal supports to act as EGC for other equipment. It permits the metal rack to be considered as being connected to an EGC if the metal rack or structure is connected to an equipment grounding conductor by one of the means indicated in 250.134. In general, this means that metal enclosures supported by the metal rack are grounded with an EGC of the wire type that is contained within the raceway, or cable, containing the circuit conductors supplying the equipment. This simply recognizes that the metal support structure can be considered as being connected to an EGC.

Reconditioned electrical equipment?

There are multiple new requirements in the 2020 NEC for reconditioned electrical equipment. Does this prohibit an electrical contractor from installing used equipment that is still in good shape? I have seen refurbished equipment advertised. Is that to be reconditioned?

First, we must address used equipment, which is not reconditioned equipment. In order to answer your question, we must refer to the general definition of “reconditioned” in Article 100. This definition contains two sentences. Reviewing them one at a time will allow us to fully understand what is, and what is not considered to be reconditioned equipment.

In the NEC , the word “reconditioned” means electromechanical systems, equipment, apparatus or components that are restored to operating conditions. Electromechanical systems are mechanical and electrically operated. The word “apparatus” means technical equipment or machinery needed for a particular activity or purpose. The words “equipment” and “components” are commonly understood. This sentence clearly states that, in order to be considered as reconditioned, the equipment was not operating, it was not functioning properly, something was wrong, and it was necessary to take action to restore the equipment to operating condition. This points out that used equipment in operating condition is not considered to be reconditioned.

The second sentence of the definition for reconditioned: This process differs from normal servicing of equipment that remains within a facility, or replacement of listed equipment on a one-to-one basis. Normal servicing of equipment would include, but not be limited to, required maintenance and replacement of worn contacts or overcurrent devices.

This sentence clarifies that this process differs from normal servicing of equipment that remains within a facility, which is a very important part of this definition. It clarifies that the normal servicing occurs within a facility, which means that the equipment continues to reside in the same place so that there is continuity and control over the equipment, its operating condition and the condition of maintenance. We know the history of the equipment and all normal servicing that may have been performed. A facility can be a single building, a campus-style complex or multiple locations such as cell towers under single ownership.

The second sentence also clarifies that replacement of listed equipment on a one-to-one basis does not constitute reconditioning. There are new requirements in the NEC that permit reconditioning equipment under prescribed conditions and, in some cases, these rules prohibit reconditioning.

An informational note that follows the definition provides clarity by explaining that the term reconditioned is frequently referred to as rebuilt, refurbished or remanufactured. These new requirements for reconditioned equipment are safety-driven and are intended to ensure the integrity of electrical distribution systems and utilization equipment.

It is imperative to require that all electrical equipment meet the requirements of applicable product standards and all manufacturers’ instructions. Just as seen in Section 90.1(A) that outlines the purpose of the NEC , it is practical to provide requirements to ensure the integrity of electrical equipment to safeguard people and property from hazards arising from the use of electricity.

OSHA and the NEC ?

Does the NEC require that electrical equipment be approved by OSHA? The informational note in 110.3(C) seems to infer that OSHA approval is required.

No. The general requirement in 110.3(A) lists the considerations of electrical equipment for suitability in installations governed by the NEC . Section 110.3(B) requires equipment that is listed, labeled or both be installed and used in accordance with any instructions included in the listing or labeling. Section 110.3(C) was added in the 2017 NEC revision cycle to address product testing, evaluation and listing (product certification) and requires that these functions be performed only by recognized qualified electrical testing laboratories.

Additionally, this requirement mandates that product testing, evaluation and listing be in accordance with applicable product standards recognized as achieving equivalent and effective safety for equipment installed to comply with the NEC . The informational note does not contain requirements. It does reference the fact that OSHA recognizes qualified electrical testing laboratories that perform evaluations, testing and certification of products to ensure that they meet the requirements of both the construction and general industry OSHA electrical standards. The informational note also states that when product certification is done under a qualified electrical testing laboratory program, the listing mark signifies that the tested and certified product complies with the requirements of one or more appropriate product safety test standards.

About The Author

DOLLARD is retired safety coordinator for IBEW Local 98 in Philadelphia. He is a past member of the NEC Correlating Committee, CMP-10, CMP-13, CMP-15, NFPA 90A/B and NFPA 855. Jim continues to serve on NFPA 70E and as a UL Electrical Council member. Reach him at [email protected].


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