Equipotential bonding grid & ground rod

[70runner]

New owner, older pool (circa 1980s). There is a grounding rod near my pool equipment pad. It is currently connected to the equipotential bonding grid (couple pumps, blower, heater). As far as I can tell this grid only includes the pool equipment and not the pool structure. As I understand it, the grounding rod should be directly connected to the ground bus of the detached pool subpanel and not the bonding grid. Is that correct?

Should be bonding grid include the subpanel housing?

 

[tim5055]

I am not an electrician, but I do not think that is correct. I do not believe there should ever be a connection between the bonding grid and the house wiring.

Part 680.26 states:

680.26 Bonding.

(A) Performance. Bonding as required by this section is intended to help reduce or eliminate voltage gradients in the pool area by forming a common bonding grid. Bonding is not required to provide a low-impedance ground-fault current path.

FPN: The bonding requirements contained in this section are not intended to require an 8 AWG copper conductor to be bonded to a panelboard, service equipment or electrode.

(B) Bonded Parts. The following parts of a pool, outdoor spa or hot tub shall be bonded to a common bonding grid of the type specified in 680.26(C).

(1) Metallic Parts of Structure. All metallic parts of the water structure, including the reinforcing metal of the pool shell, coping stones, and deck, shall be bonded to a common bonding grid [680.26(C)]. Steel tie-wires made up tight are suitable for bonding reinforcing steel together. Figure 680-19 un680-19 680-26B1 01.cdr

(2) Underwater Lighting. Metal forming shell used to contain underwater pool, outdoor spa, and hot tub luminaires and speakers.

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

(4) Electrical Equipment. Metal parts of electric equipment associated with the pool, outdoor spa and hot tub water circulating system, such as water heaters and pump motors.

Where a double-insulated water-pump motor is installed, a solid 8 AWG copper conductor shall be provided from the bonding grid to an accessible point in the motor vicinity.

(5) Metal Wiring Methods and Equipment. Metal piping, fixed metal parts, observation stands, towers, platforms, or diving structures, as well as metallic surfaces of electrical equipment located within 5 ft horizontally of the inside walls of the pool, outdoor spa or hot tub, and within 12 ft above the maximum water level.

Author's Comment: Bonding is required for diving structures, sliding glass door frames, windows, fences, screen enclosures, heater equipment, and the metal cases of electrical equipment, such as the blower, chlorinator, etc. located within 5 ft of the water’s edge.

(C) Common Bonding Grid. The metallic parts of a pool, outdoor spa or hot tub specified in 680.26(B) shall be electrically bonded to a common bonding grid by a solid conductor not smaller than 8 AWG. The termination of the bonding conductor shall be made by exothermic welding, or clamps labeled (listed) as being suitable for the purpose. The common bonding grid can consist of any of the following: Figure 680-20 un680-20 680-26C.cdr
(1) The structural reinforcing steel of the concrete pool, outdoor spa or hot tub that is secured by steel tie-wires.
(2) The wall of a bolted or welded metal pool.
(3) A solid copper conductor, insulated, covered or bare, not smaller than 8 AWG

The bonding grid is a relatively new addition to the NEC and there is still much confusion over its implementation.

I would recommend contacting your "Authority Having Jurisdiction (AHJ) and speak with an electrical inspecotor or plans reviewer. They can advise what version of the code your AHJ has adopted and what requirement are in place. Most probably your older pool is grandfathered under the old code.

 

[danpik]

Re: Equipotential bonding grid & ground rod

Ground rods are not used nor required for a bonding loop/grid/system, etc. Ground rods are required for service installations, including sub panels. current NEC requirements for ground rods is 1 rod with measured 25 ohms or less resistance or two rods connected together 6 feet apart. Someone mistakenly drove that rod thinking that any bonding current would drain off that way. All it is really doing as it is now is putting the earth near it into the same voltage potential as the components it is connected to. Your sub panel from the main should have 4 wires feeding it (2 hots, one neutral and one ground). The pool should have a copper wire buried around the perimeter of the pool and connected to at least 4 equally space points. It is then connected to the water bond and the pump(s)heater and other components

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I am not an electrician, but I do not think that is correct. I do not believe there should ever be a connection between the bonding grid and the house wiring.

While it is true that there is no intentional connection to the service ground, there is an inadvertent one thru the chassis of the pump or heater where both the ground and bond connect

 

[tim5055]

Re: Equipotential bonding grid & ground rod

Ground rods are not used nor required for a bonding loop/grid/system, etc. Ground rods are required for service installations, including sub panels. current NEC requirements for ground rods is 1 rod with measured 25 ohms or less resistance or two rods connected together 6 feet apart. Someone mistakenly drove that rod thinking that any bonding current would drain off that way. All it is really doing as it is now is putting the earth near it into the same voltage potential as the components it is connected to. Your sub panel from the main should have 4 wires feeding it (2 hots, one neutral and one ground). The pool should have a copper wire buried around the perimeter of the pool and connected to at least 4 equally space points. It is then connected to the water bond and the pump(s)heater and other components

- - - Updated - - -



While it is true that there is no intentional connection to the service ground, there is an inadvertent one thru the chassis of the pump or heater where both the ground and bond connect

As he has a pool built in 1980, decades before the bonding grid was added to the electrical code I doubt if he has any "bonding" at all. From his description I'm going to assume he has a ground rod and the pump is grounded to it and probably the panel.

The bonding requirement was added to the NEC in the 2005 edition and it depends on If/when the AHA adopted the 2005 code. Heck, I have heard of some locations that still use the 2008 code today....

 

[70runner]

I am not an electrician, but I do not think that is correct. I do not believe there should ever be a connection between the bonding grid and the house wiring.

Part 680.26 states:
FPN: The bonding requirements contained in this section are not intended to require an 8 AWG copper conductor to be bonded to a panelboard, service equipment or electrode.

The bonding grid is a relatively new addition to the NEC and there is still much confusion over its implementation.

I would recommend contacting your "Authority Having Jurisdiction (AHJ) and speak with an electrical inspecotor or plans reviewer. They can advise what version of the code your AHJ has adopted andwhat requirement are in place. Most probably your older pool is grandfathered under the old code.

You nailed this. Interpretation of this Fine Print Note is what I've been struggling with...precisely because of what danpik notes in his followup... that the bonding grid is indirectly connected to ground (and a ground rod if appropriate) via the pump/heater bonding lug and EGC. How is this different electrically from a "not intended to require" direct connection?

As to the AHJ, this is just a small sample of issues with how the pool electrical system was arranged, not the least of which is the feeder to the pool subpanel is located in a Zinsco panel (about to be replaced) and uses twin #12awg conductors off each 40 amp CB. Got lotsa stuff to work on.

 

[Bama Rambler]

By the "not intended to require" statement, they mean that you don't have to extend the bonding grid to the sub panel or intentionally ground it to a rod, but they don't prohibit the bonding grid being connected to the grounding system. Some countries prohibit the bonding grid from being connected to the grounding system at all.

 

[danpik]

How is this different electrically from a "not intended to require" direct connection?

All I can say is, "Welcome to the NEC"

 

[tim5055]

All I can say is, "Welcome to the NEC"

I wouldn't restrict it to the NEC. Any/all of the building codes have issues because they are created by committee and then a governing body gets to decide if they are going to adopt, not adopt, adopt some parts or adopt with amendments.

If you want to have interesting reading search out some of the electrical forums and look at the discussions regarding pool bonding. It will shock your world.

 

[danpik]

I wouldn't restrict it to the NEC. Any/all of the building codes have issues because they are created by committee and then a governing body gets to decide if they are going to adopt, not adopt, adopt some parts or adopt with amendments.

If you want to have interesting reading search out some of the electrical forums and look at the discussions regarding pool bonding. It will shock your world.

I am a member on three different electrician forums. Believe me, I know. It is amazing how many supposed experts still don't understand what the bonding does. Heck, I have seen where electricians think that a ground rod will clear a fault on a residential circuit, or any circuit for that matter.

 

[70runner]

Re: Equipotential bonding grid & ground rod

By the "not intended to require" statement, they mean that you don't have to extend the bonding grid to the sub panel or intentionally ground it to a rod, but they don't prohibit the bonding grid being connected to the grounding system. Some countries prohibit the bonding grid from being connected to the grounding system at all.

I guess they use a lot of double insulated pumps and what to do about the heater & blower?

After sifting though all this, my plan is to uninsulated 8awg copper bond the 2 pumps, heater, and blower, remove the direct bond to ground rod connection, and not extend the grid directly to the subpanel. Tie the subpanel to the ground rod and call it a good NEC day.

 

[danpik]

Unfortunately, what you are doing will, in reality, be useless as a bonding grid.

There is currently another thread going on that has a problem with it's bonding grid. It may help explain why the bonding grid is needed

The real need for bonding is not the pumps and heater, but instead, it is the pool water, structure and surfaces around it. These are where the voltage gradients show up that cause the problems. Don't get me wrong, there can be voltage gradients between the mechanical systems as well and these are tied into the bonding system around the pool as well. As I stated earlier, the ground rod was mistakenly driven in the thought that any "stray Voltage" would drain off to the earth thru the rod, What it is really doing, is bringing the voltage potential of the earth into the same potential as the pool equipment. at one time in the past there was no clear NEC requirement on ground rods for sub panels so I imagine the original installer thought it would be safer to "ground" the pool equipment. This mistaken grounding actually provides no short circuit protection for the equipment. This is the job of the feeder/supply wiring ground lead.

 

[70runner]

I don't disagree with the ineffectiveness of this bonding grid beyond the pool pad equipment. To achieve NEC bonding grid nirvana, I would need to cut a trench around the pool cool decking, lay a copper bonding wire, tie it to the light nitch (another circuit in another panel), trench the bonding wire to the pool pad grid, then add a water bond. An expensive, major construction project.

As to the NEC requirement for a detached subpanel GEC/ground rod, I believe that's pretty straightforward.

If the other thread is the one I'm thinking of, in that case it would seem an incomplete pool structure grid (3 sides only) may be worse than no grid at all. Which begs the question, how does one determine if his/her NEC certified, all inclusive pool bonding grid is adequate?

 

[danpik]

I don't disagree with the ineffectiveness of this bonding grid beyond the pool pad equipment. To achieve NEC bonding grid nirvana, I would need to cut a trench around the pool cool decking, lay a copper bonding wire, tie it to the light nitch (another circuit in another panel), trench the bonding wire to the pool pad grid, then add a water bond. An expensive, major construction project.

It entirely possible that there is a grid under/in the deck. However, when I see a pump motor bond hooked to a ground pin, it is not usually the case. Check your deck box for your light connection. There may be a bonding wire in there too, connected to the niche. This would give you some sort of indication as to if there is any hope for a grid/loop

As to the NEC requirement for a detached subpanel GEC/ground rod, I believe that's pretty straightforward.

Yes, no brainer. However, how it is connected to the sub panel can be a bit of a mystery to some. The sub, by todays code, should have 4 wires (240 system) running to it from the main. There will be 2 hots, one white Neutral and a green or bare copper ground wire. If there are 4 wires, the neutral should be floating (not bonded to the box/ground) and the ground rod will be attached to the ground bar.

If the other thread is the one I'm thinking of, in that case it would seem an incomplete pool structure grid (3 sides only) may be worse than no grid at all. Which begs the question, how does one determine if his/her NEC certified, all inclusive pool bonding grid is adequate?

That is the one. It does go to show how effective the copper wire is in the concrete. three sides show no potential difference while the one side that has no wire does show the difference in potential