Here's how a joint-venture of electrical contractors met NEC Article 680 requirements in their installation of 52 wet-niche fixtures in this world-class aquatic facility.
The installation of 52 underwater wet-niche lighting fixtures (24 in the diving pool and 28 in the competition pool) in this world-class aquatic facility required strict compliance with a number of provisions of Article 680 in the National Electrical Code. These requirements are worth detail study, so let's use the accompanying drawings to see how Code compliance was achieved.
NEC requirements met by installing contractor
The installing contractor, a joint venture of Cleveland Electric Co. and Yukon Electric Co., faced many NEC requirements in their task. The following is a listing of these requirements.
Sec. 680-20(a)(1) requires any underwater lighting fixture (line-voltage, or low voltage, wet-niche or dry-niche) be designed in such a way that it will prevent electric shock from any combination of fault conditions, when in use without protection by a ground fault circuit interrupter (GFCI). However, the next paragraph mandates that any underwater fixture operating at a voltage over 15V, such as a 120V underwater fixture (as in this case), must be GFCI-protected to prevent shock hazards during relamping. In the Aquatic Center, this provision is accomplished by the use of 20A, 120V, GFCI-type circuit breakers in the lighting panelboards.
Sec. 680-20 (a)(2) establishes 150V as the maximum allowable supply voltage for underwater lighting fixtures. This is a logical requirement, since incandescent lamps are the usual light source for these applications.
Sec. 680-20 (a)(3) sets a limitation on mounting distance of a fixture below water level. When installed, the top edge of the fixture must be at least 18 in. below the normal water level, as seen in Fig. 2, on page 63. The intent here is to keep the fixture away from a person's chest area, because this is the vital part of the body concerning electric shocks in swimming pools. Thus, the chest of a swimmer, who is hanging onto the edge of the pool, would not normally be against the fixture.
Sec. 680-20(a)(4) says that a wet-niche fixture, if of the type requiring submersion in the water for proper cooling, must have some type of low water detector or cutoff integral to the fixture to prevent overheating if contact with pool water is not maintained. This type of fixture must be marked "Submerse Before Lighting." The product sheer for the wet-niche fixture used at the Aquatic Center provides clear instructions. It states the following: "Low water safety sensor probe must be at top of light assembly when installed."
Sec. 680-20(b)(1) requires that conduit be used between the forming shell and the junction box or transformer enclosure (if low voltage lamps are used). The conduit must be rigid metal or IMC made of brass or other approved corrosion-resistant metal, or it may be rigid nonmetallic conduct. Use of rigid nonmetallic conduit requires a No.8 AWG insulated copper equipment grounding conductor run in the conduit and connected to the junction box or transformer enclosure and the metal forming shell of the fixture. The wording of this provision eliminates any question about the need for brass or other corrosion-resistant metal when either rigid or intermediate metal conduit is used. It is required. Of course, it's important to remember that if rigid nonmetallic conduit is used (as was done in the Aquatic Center), it must be sized large enough to allow the insertion of both the fixture cord and the insulated No. 8 AWG equipment grounding conductor.
The insulated copper equipment grounding conductor required with rigid nonmetallic conduit is terminated at an approved grounding terminal in the junction box (or transformer enclosure) and at the inside terminal of the grounding/bonding terminal on the fixture's forming shell. This conductor has an equipment grounding function, not a bonding function. It's in addition to, and of a completely different function than, the No. 8 bonding conductor usually connected to the external bonding lug.
The bonding conductor, which must be solid, connects the forming shell to the common bonding grid, as required by Sec. 680-22(a) and (b). The No. 8 insulated copper equipment grounding conductor must be stranded, however. (Sec. 310-3 requires all No. 8 and larger conductors in raceway to be stranded.) The two exceptions given do not apply here. And it's important to also remember that Sec. 310-12(b) will normally require that the insulation be colored green.
Sec. 680-20(b)(2) requires the fixture-cord jacket end and the conductor terminations within the fixture be covered by, or encapsulated in, a suitable waterproof or potting compound. In addition, the inside forming shell termination of the grounding conductor also must be covered with the same type of material because, as experience has shown, corrosion occurs if these connections are exposed to pool water. Note, in Fig. 2, that the fixture on the Aquatic Center project uses an inside/outside grounding/bonding terminal.
Also, as seen in Fig. 2, the stainless steel forming shell has a 1-in. threaded conduit entry for the 1-in. PVC, Schedule 40 conduit run from the junction box. This conduit contains the supply cord, which consists of three No.10 insulated conductors. The cord is terminated at a lamp socket for a 500W, 120V reflector lamp; the end of the cord within the fixture is also encapsulated in a suitable potting compound [epoxy resin], as required.
Sec. 680-20(b)(3) states that a wet-niche underwater light fixture must be secured and grounded to the forming shell by a positive locking device that ensures a low-resistance contact. This locking device requires a tool for removing the fixture from the forming shell. This provision, which is accomplished in the fixture's design, provides added assurance that the fixture will remain grounded because the metal forming shell provides a bond between the race-way (or No. 8 AWG insulated copper conductor in PVC) connected to the forming shell and the noncurrent-carrying metal parts of the fixture.
Sec. 680-21 covers the junction boxes and enclosures used in conjunction with pool fixtures. On the Aquatic Center project, the junction box is used only as a splicing point for the fixture and branch circuit conductors. At the Aquatic Center, the fixture cord of a wet-niche fixture is spliced to the branch circuit home run conductors extending back to the panelboard.
The use of a flush deck box to feed line-voltage lighting fixtures is no longer permitted (except where approved dry-niche fixtures include flush boxes as part of an approved assembly). The reasoning is that deck boxes installed flush in the concrete adjacent to a pool have been major sources of failure of branch circuit, grounding, and fixture conductors due to water accumulation within the box. (An exception to the basic rule allows a flush box for a low voltage lighting fixture).
In all cases, junction boxes must be made of a corrosion-resistant material and come with threaded hubs or bosses for conduit connection. They also must have an integral, approved, corrosion-resistant means for ensuring electrical continuity. These boxes have their own listing category and are constructed very differently than the usual weatherproof junction boxes.
Sec. 680-21(a)(4) gives the minimum requirements for elevation and distances involving installation of junction boxes. They cannot be less than 8 in. above the maximum water level and must be at least 4 in. above the ground or pool deck, whichever provides the greatest elevation. Additionally, they cannot be less than 4 ft from the inside of the pool, unless separated from the pool by a permanent barrier, such as a wall. These requirements are seen in Fig. 2.
Sec. 680-21(c) warns against creating a hazard where junction boxes are elevated as required. They must have physical protection against damage if located on the walkway around the pool. For that reason, they may be installed under a diving board or adjacent to a permanent structure. Sec. 680-21 (e) requires strain relief in swimming pool junction boxes so anyone inadvertently pulling on the fixture cord while relamping won't disturb the grounding connections.
At the Aquatic Center, the junction boxes are in three large enclosures spaced along the north side of the pool deck, more than 20 ft back from the pool edge. Each is mounted inside an architecturally designed, 3-ft-high monument having a 120V duplex GFCI receptacle and a suitable cover. The junction boxes are located behind a faceplate containing flush receptacles for electrical and electronic timing equipment; these receptacle circuits are low-voltage signal circuits. On the south side of the Center, the three enclosures (and timing faceplates) are recessed into the wall of the permanent stands.
As Fig 2 shows, junction boxes are usually intended to be supported by the entering raceways; this supporting method involves other Code provisions. Specifically, Sec. 347-3(b) forbids the use of rigid non-metallic conduit to support equipment, and a box is clearly equipment, given the definition in Article 100. Therefore, and in accordance with Sec. 370-23 (d), these boxes must be supported by rigid or intermediate metal conduit, secured not more than 18 in. away.
Sec. 680-22 (Bonding) requires that, in general, all metal parts within 5 ft of the inside walls of a pool and not separated by a permanent barrier as well as all metal parts of electrical equipment associated with the pool water circulating system must be bonded together. That usually includes, in addition to the forming shells of underwater lights, ladders, rails, reinforcing bars, and equipment in the pump room.
The objective of bonding all metal together and then grounding the interconnected metal components is to bring everything within touch to the same electrical potential, thereby eliminating voltage gradients. Studies have shown that a swimmer with water in his ears exposed to voltage gradients as low as 4V can become disoriented and drown.
Sec. 680-22(a) spells out, in detail, the components that must be bonded together. A generalization can be made that all metal parts within 5 ft of the inside walls of the pool not separated by permanent barrier and all metal parts of electrical equipment associated with the pool water circulating system must be bonded together. Note that bonded together does not mean that all of these parts must be connected to each other. In this instance, it means that these parts be connected to a common bonding grid by means of a No. 8 AWG solid copper conductor. At the Aquatic Center, the grid is a No.8 AWG solid copper conductor installed underground and under the pool deck, except where it extends into the pump (mechanical) rooms.
Sec. 680-24 lists equipment that must be grounded. These include wet- and dry-niche underwater lighting fixtures, all electrical equipment within 5 ft of inside walls of the pool, all electrical equipment associated with the recirculating system of a pool, junction boxes and transformer enclosures, and panelboards supplying any electrical equipment associated with a pool.
Required grounding methods are given in Sec. 680-25. The importance of understanding the difference between bonding and grounding becomes evident when the provisions of this section are considered. Essentially, this section calls for grounding using an equipment grounding conductor run in conduit with the supply conductors. Also, all equipment grounding conductors must be terminated at an equipment grounding terminal. On the other hand, the grounding conductor required by Sec. 680-22 does not have to be in conduit; it may be connected directly to enclosures.
Aquatic Center background information
The general contractor for the project is Gaston-Thacker/Whiting-Turner. Architectural design was a joint venture by Stanley, Love-Stanley. P.C. and Smallwood, Reynolds, Stewart, Stewart & Associates, Inc. The electrical engineers were Newcomb & Boyd. The electrical installation was performed as a joint venture project by Cleveland Electric Co., with Gerald "Mac" McDaniel as contract manager, and Yukon Electric Co., with Don Sheffield as general foreman. All firms are in Atlanta.