2011 The Top Revisions to this Edition of the NEC

Editor's note: In this month's article, Mike Holt focuses on bonding and grounding electrical circuits.

450.14 Disconnecting Means

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A new section will require a disconnecting means for most transformers.

450.14 Disconnecting Means. For transformers other than Class 2 and Class 3, a means is required to disconnect all transformer ungrounded primary conductors. The disconnecting means must be located within sight of the transformer unless the location of the disconnect is field-marked on the transformer and the disconnect is lockable. (Fig. 17)

Analysis: Although many Code users have believed that this requirement already existed, in previous NEC editions transformers were one of the only pieces of equipment that didn't require a disconnecting means. Although there were no documented injuries to warrant this change, it's hard to argue that this requirement doesn't enhance safety.

517.16 Receptacles with Insulated Grounding Terminal

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Receptacles with insulated grounding terminals are no longer allowed in a patient care area.

517.16 Receptacles With Insulated Grounding Terminals. Receptacles having insulated grounding terminals (isolated ground receptacles) [250.146(D)] aren't permitted to be installed in patient care areas. (Fig. 18)

Analysis: In a rather substantial change to the health care provisions, isolated ground receptacles are no longer permitted in patient care areas. The wiring method in these locations requires two equipment grounding conductors — one of the wiring method type; the other in the form of an insulated green conductor [517.13]. Using an isolated ground receptacle defeats the entire concept of this dual equipment ground concept by effectively removing the metal wiring method equipment grounding conductor. In these areas, the patient is often involved in an invasive procedure, meaning the human skin is broken, typically by an incision. When this is the case, the patient is much more vulnerable to electric shock. In fact, current applied directly to the circulatory system of the patient can easily cause death at current levels lower than even a GFCI will protect against. Previous editions of the NEC included an Informational Note telling the Code user that the use of these receptacles was a bad idea in these areas. With this change, the Code rule now recognizes that fact and prohibits the practice altogether.

680.26 Equipotential Bonding

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The requirements for swimming pool bonding were revised…again.

680.26(B)(2) Perimeter Surfaces. An equipotential bonding grid must extend 3 ft horizontally beyond the inside walls of a pool, outdoor spa, or outdoor hot tub, including unpaved, paved, and poured concrete surfaces. Perimeter surfaces less than 3 ft that are separated by a permanent wall or building 5 ft in height or more require an equipotential bonding grid on the pool side of the permanent wall or building.

The bonding grid must comply with (a) or (b) and be attached to the conductive pool reinforcing steel at a minimum of four points uniformly spaced around the perimeter of the walls of a pool, outdoor spa, or outdoor hot tub.

1. Structural Reinforcing Steel. Unencapsulated structural reinforcing steel in concrete shells secured together by steel tie wires [680.26(B)(1)(a)].

2. Alternative Copper Conductor Grid. Where the structural reinforcing steel isn't available (or is encapsulated in a nonconductive compound, such as epoxy), an equipotential bonding grid meeting all of the following requirements must be installed (Fig. 19):

   1. The bonding grid must be 8 AWG solid copper, arranged in the manner described in 680.26(B)(1)(b)(3).

   2. The bonding grid must follow the contour of the perimeter surface extending 3 ft horizontally beyond the inside walls of pool.

   3. Listed splicing devices must be used.

   4. The grid must be secured in or under the deck or unpaved surface within 4 in. to 6 in. of the underside of the deck.

(3) Metallic Components. Metallic parts of the pool, outdoor spa, or outdoor hot tub structure must be bonded to the equipotential grid.

4) Underwater Metal Forming Shells. Metal forming shells and mounting brackets for luminaires and speakers must be bonded to the equipotential grid.

(5) Metal Fittings. Metal fittings sized 4 in. and larger that penetrate into the pool, outdoor spa, or outdoor hot tub structure, such as ladders and handrails, must be bonded to the equipotential grid.

(6) Electrical Equipment. Metal parts of electrical equipment associated with the pool, outdoor spa, or outdoor hot tub water circulating system, such as water heaters and pump motors and metal parts of pool covers, must be bonded to the equipotential grid.

Ex.: Metal parts of listed double insulation equipment isn't required to be bonded to the equipotential grid.

Double-Insulated Water-Pump Motors. If a double-insulated water-pump motor is installed, a solid 8 AWG copper conductor from the bonding grid must be provided for a replacement motor.

Pool Water Heaters. Pool water heaters must be grounded and bonded in accordance with equipment instructions.

(7) Fixed Metal Parts. All fixed metal parts must be bonded to the equipotential grid, including but not limited to metal-sheathed cables and raceways, metal piping, metal awnings, metal fences, and metal door and window frames.

Ex. 1: If separated from the pool, outdoor spa, or outdoor hot tub structure by a permanent barrier that prevents contact by a person.

Ex. 2: If located more than 5 ft horizontally of the inside walls of the pool, outdoor spa, or outdoor hot tub structure.

Ex. 3: If located more than 12 ft measured vertically above the maximum water level.

(C) Pool Water. Pool water must have an electrical connection to one or more of the bonded parts described in 680.26(B). If none of the bonded parts is in direct connection with the pool water, the pool water must be in direct contact with an approved corrosion-resistant conductive surface that exposes not less than 9 sq in. of surface area to the pool water at all times, and it must be bonded in accordance with 680.26(B). (Fig. 20)

Analysis: This section has been revised extensively over the last few Code change cycles, and this one is no exception. Recent revisions have left gaping holes in the requirements not to mention plenty of room for misunderstanding, misinterpretation, and misapplication. The changes in the 2011 edition of the NEC seek to remedy these problems.

The connection of the copper bonding grid discussed in 680.26(B)(1)(b)(1) has been addressed. When nonconductive structural reinforcing steel is used in a pool, a bonding grid of 8 AWG copper conductors is required, but previous editions of the Code didn't address how to connect the grid to itself. This NEC cycle clarifies that the grid must be bonded together at all points of crossing in the grid, and the bonding means must comply with the connection provisions of 250.8. Also, 680.26(B)((2)(b) was revised, requiring a copper grid instead of the single conductor permitted in 2008. Fortunately, this provision isn't used often as it would be an incredibly time consuming and expensive solution.

A clarification was also made regarding the bonding of the pool deck. It isn't uncommon for a pool deck to be less than 3 ft when a wall, fence, or other structure is near the pool. Previous editions of the Code didn't tell the user how to handle the situations, but now it's clear that the bonding doesn't need to extend to the other side of the wall, provided the wall (or fence) is no less than 5 ft in height.

The bonding of nonelectric metal parts has been clarified. Section 680.26(B)(7) has long required that “metal wiring methods and equipment” be bonded to the equipotential grid discussed in this section. One question that often comes up, however, is whether the “equipment” contemplated in this rule applies to only “electrical equipment,” as defined in Art. 100 — or if it's intended to apply to all equipment, including nonelectrical equipment. This change clarifies that this provision does, in fact, apply to nonelectrical equipment, such as metal fences and similar items.

Lastly, the exception allowing for a permanent barrier separating metal parts has been clarified. A change to the exception makes it clear that such a barrier must prevent a person from contacting metal parts and equipment that aren't bonded.

680.73 Accessibility

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The accessibility of the receptacle supplying a hydromassage tub has been revised.

680.73 Accessibility. Electrical equipment for hydromassage bathtubs must be capable of being removed or exposed without damaging the building structure or finish. Where the hydromassage bathtub is cord-and plug-connected with the supply receptacle accessible only through an access opening, the receptacle must face toward the opening and be within 1 ft of the opening.

Analysis: When a hydromassage tub is cord- and plug-connected, it isn't uncommon to find the receptacle beneath the tub arranged in a manner that makes it nearly impossible to see, much less use. Oftentimes, these receptacles are several feet away from the access opening, facing away from the person trying to access the receptacle. This change now requires that such a receptacle be installed close to the access opening (within 1 ft), and it must also be facing toward the opening.

690.47 Grounding Electrode System

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The requirements for PV grounding electrode systems have been greatly revised.

690.47 Grounding Electrode System.

(B) Direct-Current Systems. If installing a DC system, a grounding electrode system must be provided in accordance with 250.166 with a grounding electrode conductor in accordance with 250.64.

A common DC grounding-electrode conductor is permitted to serve multiple inverters with the size of the common grounding electrode and the tap conductors in accordance with 250.166. The tap conductors must be connected to the common grounding-electrode conductor in such a manner that the common grounding electrode conductor remains without a splice or joint.

(C) Alternating-Current (AC) and Direct-Current (DC) Grounding Requirements. PV systems with DC modules having no direct connection between the DC grounded conductor and AC grounded conductor must be bonded to the AC grounding system by one of the methods listed in (1), (2), or (3).

Note 1: ANSI/UL 1741, Standard for Inverters, Converters, and Controllers for Use in Independent Power Systems have the grounding electrode conductor (GEC) connection point identified. In PV inverters, the terminals for the DC and AC equipment grounding conductors common with each other are marked DC GEC terminal.

Note 2: For utility-interactive systems, the existing premises grounding system serves as the AC grounding system.

1. Separate DC Grounding Electrode System Bonded to the AC Grounding Electrode System. A separate DC grounding electrode bonded to the AC grounding electrode system with a bonding jumper sized to the larger of the existing AC grounding electrode conductor or DC grounding electrode conductor specified by 250.166.

   The DC grounding electrode conductor or bonding jumper to the AC grounding electrode system can't be used as the required AC equipment grounding conductor.

2. Common DC and AC Grounding Electrode. A DC grounding electrode conductor sized in accordance with 250.166 run from the marked DC grounding electrode connection point to the AC grounding electrode.

   Where an AC grounding electrode isn't accessible, the DC grounding electrode conductor is permitted to terminate to the AC grounding electrode conductor by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process [250.64(C)(1)].

   The DC grounding electrode conductor or bonding jumper to the AC grounding electrode system can't be used as the required AC equipment grounding conductor.

3. Combined DC Grounding Electrode Conductor and AC Equipment Grounding Conductor. An unspliced, or irreversibly spliced, combined equipment grounding/grounding electrode conductor run from the marked DC grounding electrode connection point along with the AC circuit conductors to the grounding bus bar in the associated AC equipment.

   The combined equipment grounding/grounding electrode conductor must be sized to the larger of 250.122 or 250.166 and be installed in accordance with 250.64(E).

Analysis: Section 690.47(B) has been revised to clarify that a common grounding electrode conductor can be used to ground multiple inverters. This concept isn't new to the NEC, as similar provisions can be found in 250.30 for separately derived systems. As you can see, (C) has been extensively revised again. Changes to this edition of the NEC are intended to incorporate the concepts of the 2005 and 2008 editions into clear, easily understandable text.

In a somewhat surprising change, 690.47(D) was deleted. That section required that ground and pole-mounted PV arrays have a grounding electrode. This requirement was added in the 2008 edition and was intended to be optional. But the language that was used made it mandatory. By removing the rule altogether, it's still optional, but now isn't mandatory.