This article was posted 09/08/2005 and is most likely outdated.

Grounding versus Bonding, Part 11 of 12
 

 
Topic - Grounding versus Bonding, Part 11 of 12
Subject - Pools, fountains, and similar installations

September 8, 2005 

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Grounding versus Bonding, Part 11 of 12

Pools, fountains, and similar installations

Mike Holt for EC&M Magazine

The bonding and grounding requirements of pools can make you feel like you're in over your head.

What comes to mind when you think of pools, spas, hot tubs, and similar installations? Most people would say fun and relaxation. But the person trying to properly ground and bond these is more likely to say confusion and frustration. Why? Because of a wrinkle to what we've covered thus far in this series. To help us iron out that wrinkle, let's recap three basic concepts:

  1. When you ground, you connect something to the earth. Think of this as earthing .
  2. When you bond, you create a conductive path between metallic objects.
  3. Bonding is the method by which you create a low-impedance path for fault current.

But with pools and other such installations, the NEC throws a new bit of lingo at us: equipotential bonding . The purpose of equipotential bonding is to bring metallic objects to the same potential. This reduces the shock hazard, which is obviously an important consideration for people immersed in a container of water.

The intention of equipotential bonding is to reduce earth voltage gradients in the area around a permanently installed pool or similar installation by the use of a common bonding grid per 680.26(B) and (C).

Equipotential bonding is not intended to provide a low-impedance ground-fault current path to the source (which would assist in clearing a ground fault) as required by 250.4(A)(3). It has nothing to do with creating a path for fault current. Therefore, the 8 AWG or larger solid copper equipotential bonding conductor required by 680.26(C) isn't required to extend to (or attach to) any panelboard, service equipment, or electrode.

In addition, to equipotential bonding is the requirement that any wiring method used for equipment associated with the pool, spa, or hot tub is to include an insulated copper equipment grounding (bonding) conductor. You must size this conductor per 250.122, but in no case can it be smaller than 12 AWG copper (Figure 680-7). Various other requirements apply, depending on the type of raceway used. These requirements all work toward providing an effective ground-fault current path.

Pool lights

We can all agree that the goal when wiring luminaires in a pool is to light up the pool, not its occupants. This is why branch-circuit conductors for an underwater luminaire must contain an insulated copper equipment grounding (bonding) conductor sized per Table 250.122. In no case can this conductor be smaller than 12 AWG (Figure 680-19).

The equipment grounding (bonding) conductor for the underwater luminaire must not be spliced [680.23(F)(2)], unless one of two conditions exists (Figure 680-20):

  1. More than one underwater luminaire is supplied by the same branch circuit. If so, the equipment grounding (bonding) conductor can terminate at a listed pool junction box that meets the requirements of 680.24(A).
  2. The equipment grounding (bonding) conductor terminates at the grounding terminal of a listed pool transformer, GFCI, clock switch, or manual snap switch that is located between the panelboard and a junction box connected to the conduit that extends directly to the underwater luminaire.

The branch-circuit conductors for the underwater luminaire must not occupy raceways, boxes, or enclosures containing other conductors on the load side of a GFCI or transformer-unless one of the following conditions exists:

  1. The other conductors are GFCI protected.
  2. The other conductors are grounding (bonding) conductors.
  3. The other conductors supply a feed-through type GFCI.
  4. The other conductors are in a panelboard.

Junction Boxes

The junction box (deck box) that connects directly to an underwater permanently installed pool, outdoor spa, or outdoor hot tub luminaire forming shell must be listed as a swimming pool junction box and equipped with threaded entries or a nonmetallic hub [680.24] (Figure 680-21). It also must be constructed of copper, brass, or corrosion-resistant material approved by the authority having jurisdiction. You must provide electrical continuity between all metal conduit and the grounding (bonding) terminals within the junction box.

Also, you must ensure the junction box has at least one more grounding (bonding) terminal than the number of conduit entries [680.24(D)]. Typically, there are four grounding (bonding) terminals in the junction box and three conduit entries. Finally, you must provide a strain relief at the enclosure where you terminate the flexible cord of an underwater luminaire [680.24(E)].

Bonding Metal Parts to the Equipotential Bonding Grid

Ensure the following parts of a permanently installed pool, outdoor spa, or outdoor hot tub are bonded together and to the equipotential bonding grid.

(1) All metallic parts of reinforcing metal not encapsulated with a nonconductive compound. The usual steel tie-wires that secure rebar together are considered suitable for bonding the reinforcing steel together (Figure 680-22). Where conductive reinforcing steel of the permanently installed pool, outdoor spa, or outdoor hot tub shell and deck is not available, provide-per 680.26(C)-for an alternative means to eliminate voltage gradients that would otherwise be provided by unencapsulated, bonded reinforcing steel.

(2) All metal forming shells for underwater wet-niche luminaire.

(3) Metal fittings within or attached to the permanently installed pool, outdoor spa, or outdoor hot tub structure, such as ladders and handrails.

(4) Metal parts of electrical equipment associated with the circulating system (water heaters and pump motors) and metal parts of equipment associated with pool covers.

(5) Metal cables, metal raceways, metal piping, and all fixed metal parts of electrical equipment-except those separated from the pool by a permanent barrier located within:

  • 5 ft horizontally of the inside walls of the permanently installed pool, outdoor spa, or outdoor hot tub.
  • 12 ft above the maximum water level of the permanently installed pool, outdoor spa, or outdoor hot tub; or any observation stands, towers, platforms, or diving structures.

The Equipotential Bonding Grid

All metal parts specified in 680.26(B) must be bonded to an equipotential bonding grid with a solid copper conductor not smaller than 8 AWG. The termination of the bonding conductor must be made by exothermic welding, listed pressure connectors, or listed clamps that are labeled as suitable for the purpose. An equipotential bonding grid must extend under paved walking surfaces for 3 ft horizontally from the water.

The equipotential bonding grid must be formed from either or both of:

(1) The structural reinforcing steel of a concrete permanently installed pool, outdoor spa, or outdoor hot tub, tied together by the usual steel tie wires.

(2) The metal walls of a permanently installed pool, outdoor spa, or outdoor hot tub.

But, what if neither of these is available? Where structural reinforcing steel or the walls of bolted or welded metal permanently installed pool, outdoor spa, or outdoor hot tub structures are not available, you must construct an equipotential bonding grid as follows:

(a) The equipotential grid can be constructed with 8 AWG bare solid copper conductors that are bonded to each other at all points of crossing by exothermic welding, listed pressure connectors of the set screw or compression type, listed clamps, or other listed fittings [250.8].

(b) The equipotential bonding grid must cover the contour of the permanently installed pool, outdoor spa, or outdoor hot tub, and deck extending 3 ft horizontally from the water. The equipotential bonding grid must be arranged in a 1 ft x 1 ft network of 8 AWG conductors, with a tolerance of 4 in.

All equipotential bonding terminations must be by exothermic welding, listed pressure connectors of the set screw or compression type, listed clamps, or other listed fittings [250.8].

Let's go back for a moment to a frequently misapplied term: grounding. One of the myths about grounding (earthing) is that it reduces shock hazards by bringing everything to ground potential. Because the earth is not of uniform conductivity, that can hardly be the case. Another myth is that grounding (earthing) provides a common reference point. This, also, defies logic.

What about that common reference? If ground (earth) is not it, what is? You can establish a common reference by constructing a bonding grid, not an earthing connection . Connect your bonding path to the grounding grid, and all of the objects are at an equal potential.

When you have equal potential, then by definition you do not have a voltage difference. Without a voltage difference, there can be no current flow. Thus, you use an equipotential bonding system-not a grounding system-to reduce shock hazards.

This is the final article in this series. If you've read them all, you now understand the difference between grounding and bonding-and the purpose of one vs. the other. By not confusing the two, you can eliminate some common causes of unsafe installations.

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Comments
  • WHY WOULD A PORTABLE SPA, WITH A PLASTIC BASE, AND WOOD FRAME WITH PLASTIC CABINETS, NEED THE BONDING GRID EXTENDING 3' FROM WATER'S EDGE? HOW IS IT POSSIBLE FOR SOMEONE TO GET SHOCKED BY STEPPING OUT OF THE SPA?

    BRIAN
    Reply to this comment
  • Reply from: Mike Holt   
    Visit www.MikeHolt.com, and go to the Technical link, then click on the Stray Voltage link for info on stray voltage/current.
    Reply to Mike Holt


  • When wiring a wet niche, what is the purpose of the #8insulated wire on the inside of the niche. When the light is 120V. The threaded screw goes through the the niche. Outside you use #8 uninsulated and inside #8 insulated, same point. The outside bond creates the conductive path, the insides goes to the tie box through the conduit that is attached to niche. You also have the fixture grounding wire in the cable going through the conduit to the tie box.


    Reply to this comment

  • Great series. I learned a lot (but glad it's "over"-whew). Now I always specify Ground Fault monitors/protection for pools, marinas, etc. Code is a only minimum; what's wrong with exceeding the code a little when it comes to life safety? If the owner doesn't want to spend the money, let HIM delete it.


    Reply to this comment

  • Great series. Are there any pictures to accompany the last article (12 of 12)to help the 'slow learners' who seem to need a picture. If pictures which refer to the points in article 12 appear elsewhere throughout the series, it might be helpful to reference those locations whereever applicable. Regards, TBrown, Austin, TX


    Reply to this comment

  • Mike,

    In Canada (Ontario)the ESA requires (not each municipality) that the water pipes for the pools are bonded even if they are PVC. So the common practice is to insert a metallic tube inside the PVC and bond the metalic tube That way the water is bonded even if the level of the water inside the pool is insignificantly low. Is there a practice similar like this one in USA.

    Thanks, Filip


    Reply to this comment

  • Article 680 requirements for underwater lights are a moot point for these reasons:

    1. Fiber optic underwater lights have turned 120 volts underwater lights into dinosaurs. There are some 12 volt DC light emitting diode lights on on the market which would require electricity underwater. You can also get fiber optic landscape lights and a project for 2006 is to install such lights in the pit underneath a rock crusher at work. The maintenance factors for fiber optic lights have no comparison because the bulb and color filter can be located in a dry area in the case of underwater and landscape lights. In the case of industrial lighting the light source can be located in a less corrosive, dirty, or otherwise hostile environment.

    2. Brass conduit is only available with a National Sanitation Foundation listing. Article 680 permits approved rather than listed conduit but then the inspector has to come out and examine the pipe for internal smoothness. Brass pipe is also more expensive than fiber optics.

    Michael R. Cole
    Reply to this comment

  • Actually, as electrical systems age worldwide there will be more instances of underground wiring leaking electricity into the earth, creating nasty tingle voltages on everything.

    I one time had to bond the water supply pipes and drain pipes for an ordinary bathtub to each other and the electric service grounding electrode conductor. They had a failed underground electrical line that was leaking electricity into the soil which in turn partially energized the drain pipes and basement floor. Their properly grounded washing machine had a naasty tingle voltage as well and to fix that I had to cut the power to the failed underground wiring that went to a detached garage. The underground line was about 20 or 30 feet long and was leaking 7 amps at 120 volts during a DROUGHT!

    In his book, Old Electrical Wiring, David Eli Shapiro relates how electricity was crawling up the slime inside of the plastic drainpipe for a shower. He never did find the source but it was getting the homeowner's attention. Good application for inserting a length of copper pipe in plastic pipes and bonding that.

    I have also encountered a mobile home park where tree roots and grass roots were penetrating the O-rings of gasketed 3034 PVC sanitary sewer pipe. After accounting for manholes and handholes which a made on concrete ( which is semiconductive ) there are lots of places where electricity could enter a sanitary sewer. The sanitary sewer people need to be informed that gasketed 3034 PVC sewer pipe joints need to be wrapped with copper coil or other deterrent to plant roots.

    Michael R. Cole
    Reply to this comment
  • Reply from: steetuall   
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    Reply to steetuall



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