The Differences Between Grounding and Bonding – Part 11 of 12
Courtesy of www.MikeHolt.com.
This article is the eleventh in a 12-part series on the differences between grounding and bonding.
Three Chapter 6 Articles have significant implications for grounding and bonding special equipment:
- Article 600 — Electric Signs and Outline Lighting.
- Article 680 — Swimming Pools, Fountains, and Similar Installations.
- Article 690 — Solar Photovoltaic (PV) Systems.
Electric signs and outline lighting
Metal equipment of signs, outline lighting systems, and skeleton tubing must connect to the circuit equipment grounding conductor (EGC) of a type recognized in Sec. 250.118 [Sec. 600.7(A)(1)].
If the EGC is of the wire type, size it per Sec. 250.122 [Sec. 600.7(A)(2)]. Make EGC connections per Sec. 250.130 in a method specified in Sec. 250.8 [Sec. 600.7(A)(3)].
Metal parts of signs and outline lighting systems must be bonded together and connected to the transformer or power-supply EGC [Sec. 600.7(B)(1)]. Bonding is not required if the power supply is Class 2-rated [Sec. 600.7(B)(1) Exception].
Make bonding connections per Sec. 250.8 [Sec. 600.7(B)(2)]. To bond secondary circuit conductors for neon tubing, you can use listed flexible metal conduit or listed liquidtight flexible metal conduit if the total length of the flexible metal conduit does not exceed 100 ft [Sec. 600.7(B)(4)].
Bonding conductors must be copper and at least 14 AWG [Sec. 600.7(B)(7)]. Bonding conductors installed outside a sign or raceway must be protected from physical damage.
Swimming pools, fountains, and similar installations
Many of these requirements intend to equalize potential between metal parts, thus you will see “equipotential bonding” used in Art. 680.
Terminals for grounding and bonding equipment must be identified as suitable for use in wet and corrosive environments and be listed for direct burial use [Sec. 680.7].
The wiring methods to a pool-associated motor must contain an insulated copper EGC sized per Sec. 250.122. The EGC must be at least 12 AWG [Sec. 680.21(A)(1)].
If raceway running to an underwater luminaire is metal, then it must be listed and identified as red brass or stainless steel [Sec. 680.23(B)(2)(a)].
A nonmetallic raceway run to the forming shell of a wet-niche luminaire must contain an 8 AWG insulated (solid or stranded) copper conductor that terminates to the forming shell unless a listed low-voltage lighting system that does not require grounding is used [Sec. 680.23(B)(2)(b)].
Branch-circuit [Sec. 680.23] or feeder [Sec. 680.25] wiring installed in corrosive locations must contain an insulated copper EGC sized per Sec. 250.122, but no smaller than 12 AWG. It must also be a rigid metal conduit, intermediate metal conduit, rigid polyvinyl chloride conduit, or reinforced thermosetting resin conduit [Sec. 680.14] or liquidtight flexible nonmetallic conduit [Sec. 680.23(F)(1)].
Branch-circuit conductors for all through-wall underwater pool luminaires must have insulated copper EGCs without joint or splice except as permitted in Sec. 680.23(F)(2)(a) and (b). Size branch-circuit and feeder EGCs per Sec. 250.122, but they must be at least 12 AWG.
The circuit EGC for the underwater pool luminaire cannot be spliced, except for the two applications described in Sec. 680.23(F)(2)(a) and (b).
The branch-circuit conductors for the underwater pool luminaire on the load side of a GFCI or transformer [to comply with Sec. 680.23(A)(8)] cannot occupy raceways or enclosures with other conductors unless the other conductors are [Sec. 680.23(F)(3)]:
(1) GFCI-protected or,
(2) EGCs/bonding jumpers as required by Sec. 680.23(B)(2)(b) or,
(3) Supply conductors to a feed-through-type GFCI.
The junction box [Sec. 680.24(A)], transformer enclosure, or GFCI enclosure [Sec. 680.24(B)] for an underground pool luminaire must connect to the grounding terminals of the supply-circuit panelboard [Sec. 680.24(F)] (Fig. 1).
The function of equipotential bonding is to eliminate voltage gradients in the pool area and not to provide a path for ground-fault current. Equipotential bonding in the vicinity of swimming pools reduces the potential differences (shock hazards) created by stray currents or piping connected to the swimming pool.
To accomplish equipotential bonding, the parts of a permanently installed pool listed in Sec. 680.26(B)(1) through (B)(7) must be bonded with a solid copper conductor at least 8 AWG with a listed pressure connector, terminal bar, or other listed means per Sec. 250.8(A) [Sec. 680.26(B)] (Fig. 2). This equipotential bonding is not required to extend to any panelboard, service disconnect, or grounding electrode.
Conductive pool shells must conform to Sec. 680.26(B)(1). For example, unencapsulated structural reinforcing steel bonded by steel tie wires or the equivalent [Sec. 680.26(B)(1)(a)].
Perimeter surfaces must be attached to the concrete pool reinforcing steel at a minimum of four points uniformly spaced around the perimeter of the pool [Sec. 680.26(B)(2)]. In addition, they must conform to other requirements of Sec. 680.26(B)(2)(a), (b), or (c). Many of these requirements are new with the 2020 cycle.
Metal fittings sized over 4 in. in any dimension and within (or attached to) the pool structure (e.g., ladders and handrails) must be connected to the swimming pool equipotential bonding means [Sec. 680.26(B)(5)]. As of the 2020 NEC, metallic pool cover anchors 1 in. or less in any dimension and 2 in. or less in length do not have to be bonded to the equipotential bonding means.
Metal parts of electrical equipment associated with the pool water circulating system must be connected to the swimming pool equipotential bonding means [Sec. 680.26(B)(6)].
Fixed metal parts within 5 ft horizontally [Sec. 680.26(B)(7) Exception No. 2] and 12 ft vertically [Sec. 680.26(B)(7) Exception No. 3] from the inside wall of the pool must be connected to the swimming pool equipotential bonding means. [Sec. 680.62(B)(7)].
Exception No. 1: Those separated from the pool by a permanent barrier that prevents contact by a person don’t have to be bonded.
If the pool water in a nonconductive pool structure does not have a direct electrical connection to one of the bonded parts described in Sec. 680.26(B), an approved corrosion-resistant conductive surface that is at least 9 sq in. in contact with the water must be bonded per Sec. 680.26(B) [Sec. 680.26(C)].
Where bonded items such as ladders, rails, or underwater luminaires are in direct contact with the pool water and provide the required surface area, it is considered to comply with this requirement.
Equipotential bonding of perimeter surfaces for outdoor spas and hot tubs is not required if the four conditions enumerated in Sec. 680.42(B) are met.
For fountains, the following equipment must connect to the circuit EGC [Sec. 680.54(A)]:
(1) Other than listed low-voltage luminaires not requiring grounding, all electrical equipment within the fountain or within 5 ft of a fountain inside wall.
(2) All electrical equipment associated with the recirculating system.
(3) Panelboards that are not part of the service equipment and supply any electrical equipment associated with the fountain.
Six types of parts, as listed in Sec. 680.54(B)(1) through (6), must be bonded and connected to an EGC on a fountain branch circuit.
The grounding requirements of Sec. 680.21(A), Sec. 680.23(B)(3), Sec. 680.23(F)(1), and (2), Sec. 680.24(F), and Sec. 680.25 apply to fountains [Sec. 680.55(A)]. Fountain equipment supplied by a flexible cord must have all exposed metal parts connected to an insulated copper EGC that is an integral part of the cord [Sec. 680.55(B)].
For hydromassage tubs, the five types of parts listed in Sec. 680.74(A)(1) through (5) must be bonded (for example, pump and blower motors).
Metal parts required to be bonded by Sec. 680.74(A) must be bonded using a solid copper conductor at least 8 AWG. Bonding jumpers are not required to extend to any remote panelboard, service disconnect, or any electrode [Sec. 680.74(B)].
When installing a double-insulated circulating pump or blower motor, allow for the fact the replacement might not be double insulated. To do this, terminate a bonding jumper to the EGC of the motor branch circuit, and make it long enough to terminate the other end on the replacement motor.
Solar photovoltaic (PV) systems
Exposed metal parts of PV module frames, electrical equipment, and any enclosure containing PV system conductors must connect to the PV system circuit EGC per Sec. 250.134 or Sec. 250.136 [Sec. 690.43].
Metallic support structures listed, labeled, and identified for bonding and grounding metal parts of PV systems can be used to bond PV equipment to the metal support structure that has been connected to the PV circuit EGC [Sec. 690.43(B)].
Metallic support structures used as an EGC must have identified bonding jumpers between separate metallic sections, or the support structure must be identified for equipment bonding purposes and connect to the PV circuit EGC as required by Sec. 690.43.
The bonding requirements contained in Sec. 250.97 apply only to solidly grounded PV system circuits operating over 250V to ground [Sec. 690.43(D)].
EGCs for PV system circuits must be sized per Sec. 250.122, based on the circuit overcurrent protection ampere rating [Sec. 690.45] (Fig. 3).
Where no overcurrent protective device is used in the PV system direct-current circuit, size the EGC for the system’s direct-current circuit per Table 250.122, based on an assumed overcurrent device for the circuit sized per Sec. 690.9(B).
Increases in EGC size due to voltage drop are not required.
A building or structure supporting a PV system must use a grounding electrode system installed per Part III of Art. 250 [Sec. 690.47(A)].
The PV array EGCs must connect to a grounding electrode system per Part VII of Art. 250. This connection is required in addition to the EGC requirements in Sec. 690.43(C). Size the PV array EGCs per Sec. 690.45.
For specific PV system grounding configurations as permitted in Sec. 690.41(A), apply Sec. 690.47(A)(2) if it's solidly grounded or Sec. 690.47(A)(1) if it’s not.
Special equipment, same goal
From these three Articles (600, 680, and 690), you can see there’s more to bonding some equipment than what you find in Art. 250. Equipment in Chapter 6 is there because something about it means Chapters 1 through 4 are not enough. But always, the goal of bonding is to reduce or eliminate differences of potential.
These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.
