Opinions On Bonding Pool's Equipotential Grid Directly To System Ground Electrode

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Hanstb

Hanstb

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Sep 20, 2018
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Miami, FL
Hello All,

I am curious as to the preferred practice amongst TFP experts regarding bonding the pool’s equipotential grid to the homes earth ground electrode, CEE, Ufer, etc.

NEC 680 does not require or prohibit this connection, it simply states:

“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 way I interpret NEC 680, it leaves it up to the engineer/electrician to decide whether or not to bond the pool’s equipotential grid to the home’s primary electrode.

I am neither an electrical engineer nor a licensed electrician; a professional builder built my pool, and to the best of my knowledge it is code complaint. The equipotential grid in my case is NOT bonded directly to the earth ground at the service entrance.

The reason for my curiosity is, I have always been lead to believe that multiple paths to earth on an equipment grounding circuit are undesirable and possibly dangerous, as such multiple earth grounds, if present, should be bonded together.

The pool itself is a basically a massive CEE (concrete encased electrode) and for all intensive purposes an Ufer ground, since all the pool equipment is bonded to the pool, and simultaneously connected to the homes equipment ground, wouldn’t this crate an alternate path to ground requiring that the pool’s equipotential bonding grid be bonded directly to the service entrance electrode via a direct connection utilizing a # 6 solid copper conductor? The NEC doesn’t require it, and I have been unable to get a definitive answer from my local BP, electrician, or inspector, I keep hearing “you can, but the NEC does not require it.” I have read articles by Mike Holt, a recognized expert on the National Electrical Code, and other industry sources, that while very detailed and informative, also do not address this question beyond “it's allowed but not required”, I am more interested in “is it a best practice” than if it’s required. The NEC is very detailed when it comes to the relationship between the pool and electrically served equipment, metal structures, etc., I am surprised this is not explained in greater detail within the code, or perhaps I'm just missing something.

Curiously enough Mike Holt drills down on the importance of not creating multiple paths to ground and goes into great detail in his videos and articles as to why that is unadvisable and possibly hazardous. He also has numerous articles relating to pool bonding and pool safety, but I have been unable to locate a specific answer to the question of bonding the pool grid to the primary grounding electrode beyond the text contained in the NEC which is not conclusive.

I am inclined to treat the pool as an additional ground and bond it to the primary electrode, but if anyone could offer greater insight or possibly provide additional references as to the rules and best practices, I would really appreciate it.

Thank you!
 
I will offer my personal opinion which is not to be considered TFP’s position.

The equipotential bond on a pool serves a single purpose - to ensure that the water and all metallic items and equipment in contact with the water are always connected by the lowest possible impedance pathway. The entire purpose of bonding is to ensure that the water and anything connected to it are always at the same electrical potential. Therefore, it really doesn’t matter if it’s connected to the service ground or not. Theoretically, voltage is a difference in potential energy (electrical) between two points in a circuit. So, there is no fundamental difference in a circuit if Point A is at zero volts and Point B is at 1V OR Point A is at 10,000V and Point B is at 10,001V. The difference is still 1V.

Connecting the bonding system to the earth ground really has no impact on the functional reason for having the bonding system in the first place.

I will also say that it is my understanding that, in the National electrical code, the only TRUE earth grounding point is at the main service panel and it’s at that point that the neutral bus and ground bus are tied together. So creating any additional earth grounds somewhere else in the circuit is really not “best practices”.
 
Most equipment that has a EGC (Equipment Grounding Conductor) will also be bonded (light niche, pump, heater etc.). So, the bonding grid is connected to the ground at multiple points.

As long as everything is done to code, I wouldn't go trying to overthink it. The NEC is pretty comprehensive.

I'm sure that the issue has probably been debated by the experts who write the NEC. If they thought that it was a good idea, they would require it.
 
JoyfulNoise said:
I will offer my personal opinion which is not to be considered TFP’s position.

The equipotential bond on a pool serves a single purpose - to ensure that the water and all metallic items and equipment in contact with the water are always connected by the lowest possible impedance pathway. The entire purpose of bonding is to ensure that the water and anything connected to it are always at the same electrical potential. Therefore, it really doesn’t matter if it’s connected to the service ground or not. Theoretically, voltage is a difference in potential energy (electrical) between two points in a circuit. So, there is no fundamental difference in a circuit if Point A is at zero volts and Point B is at 1V OR Point A is at 10,000V and Point B is at 10,001V. The difference is still 1V.

Connecting the bonding system to the earth ground really has no impact on the functional reason for having the bonding system in the first place.

I will also say that it is my understanding that, in the National electrical code, the only TRUE earth grounding point is at the main service panel and it’s at that point that the neutral bus and ground bus are tied together. So creating any additional earth grounds somewhere else in the circuit is really not “best practices”.
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All that tracks perfectly with my understanding, but while the equipotential bond's primary purpose is to ensure that the water and all metallic items and equipment in contact or close proximity with the water are always connected by the lowest possible impedance pathway, it also CREATES an additional earth ground, herein lies my doubt about bonding.

The pool shell and decking is essentially a concrete encased electrode; it IS an earth ground, as described in the NEC, just like an Ufer ground in slab or foundation. (At lest our pool meets the NEC requirement.)

Section 250.52(A)(3) clearly specifies what constitutes a concrete-encased electrode. The concrete-encased electrode can be bare, zinc-galvanized, or other steel reinforcing bars or rods of not less than ½ inch in diameter coated in electrically conductive material (concrete in this case). It can be installed in one continuous 20-foot length, or, if in multiple pieces, it can be connected by the usual steel tie wires, exothermic welding, welding or other effective means to create a 20-foot or greater length. A concrete-encased electrode can also be constructed using 20 feet or more of bare copper conductor not smaller than 4 AWG.

Although I agree that creating any additional earth grounds in the circuit is really not “best practices” we are doing just that by bonding the pools equipotential grid back to the pool equipment, and that is why I am asking about bonding the grid to the primary ground at the service entrance panel, to create the lowest impedance path between the two earth grounds, just as if we where bonding two grounding electrodes as per the NEC.

JamesW said:
Most equipment that has a EGC (Equipment Grounding Conductor) will also be bonded (light niche, pump, heater etc.). So, the bonding grid is connected to the ground at multiple points.

As long as everything is done to code, I wouldn't go trying to overthink it. The NEC is pretty comprehensive.
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Again I agree, and that is precisely the issue I have with not bonding the pool grid to the system ground via a direct connection, it is bonded via the equipment grounds and bonding lugs on the various pieces of electrical equipment, so in the event of a lightning strike that energizes the ground (I’m not talking about direct strikes), that pulse will travel through that equipment from one grounding point to the other, possibly damaging the equipment.

I may certainly be overthinking this, I have been guilty of that before, but I just can't shake the feeling I'm missing a piece of the puzzle. I will concede that the NEC is pretty comprehensive, but it's not always crystal clear, and in this case the reference to bonding the equipotential grid to the system ground is not definitive.

Thanks for chiming in!
 
Over-thinking it....yeah, just a bit. There’s two things to keep in mind about this topic.

First, pool bonding cares nothing about the details of the entire electrical system as a whole. It is first and foremost a redundant safety feature of pool design. It’s entire purpose is to protect you and anyone swimming in your pool from getting shocked, whether that be a little tingle from a low voltage stray current or a cardiac arrest inducing 120V/240V shock. Bonding is agnostic when it comes to grounding.

Second, building codes are not necessarily interested in the correct scientific answer to a problem. There are many requirements in the codes (plumbing, electrical, building, etc) that are not black & white / right or wrong but, rather, represent a trade-off. So yes, the pool shell acts likes a CEE....so what? If someone proposed a code based on having multiple ground points that stated “a pool shell shall not be more than XX distance away from the service panel ground” in order to minimize the potential of some stray lightening strike causing trouble, then that could easily over-burden pool designs. Pools vary in shape, size, surface types, distance to power sources, etc, etc, and so one could easily envision a pool not being built because the code becomes too restrictive.

So, in terms of safety and flexibility, bonding represents the least restrictive way of making a pool safe without overburdening the design by chasing down transient, and possibly irrelevant, electrical circuit issues. Since there's no a priori way of knowing what effect tying the bonding loop to the service ground would have on specific pools and homes, then there’s no reason to have a hard & fast rule in the code. This is likely why it’s not stated in a black & white manner but simply stated as “you can do it if you want to but it’s not required”. I doubt you’d find any electrician, or even the sainted Mike Holt, who would come down conclusively on one side or the other.

So, sure, having multiple ground points due to bonding might (or might not) create an issue with a specific pool installation, but the existence of a bonding loop for safety takes precedence over any other consideration.

I believe in Canada pool code requires the bonding system to be connected to the panel ground. But I don’t think there are any studies that show that particular arrangement to be superior to pools that are not connected to ground.
 
 
JoyfulNoise said:
So yes, the pool shell acts likes a CEE....so what?
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Your statement is the crux of my question, the pool shell is a CEE, and as such may be required to be bonded via a dedicated jumper to the ground electrode system per NEC 250.50.

I understand NEC 860 in so far as the requirements, function, and purpose of the pool's equipotential bonding grid is concerned, my question pertains only to bonding that system to the home's primary ground electrode (or ground electrode system) via a dedicated jumper, unifying the pool's shell and EP grid to the grounding electrode system in compliance with NEC 250. NEC 680 does not require this connection, and the text contained in that section would suggest it is optional:

680.26 (B): Bonded Parts. The parts specified in 680.26(B)(1) through (B)(7) shall be bonded together using solid copper conductors, insulated covered, or bare, not smaller than 8 AWG or with rigid metal conduit of brass or other identified corrosion-resistant metal. Connections to bonded parts shall be made in accordance with 250.8. An 8 AWG or larger solid copper bonding conductor provided to reduce voltage gradients in the pool area shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes.

However, NEC 250.50, by my interpretation, does require the bonding of the pool's structure and the system ground.

250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.

Exception: Concrete-encased electrodes of existing buildings or structures shall not be required to be part of the grounding electrode system where the steel reinforcing bars or rods are not accessible for use without disturbing the concrete.

The above reference clearly requires the bonding of the pool shell to the grounding electrode system, as it is PRESENT, the exception, in my case, does not apply because a connection point exists via the EP bonding grid and the concrete need not be disturbed to install the jumper.

250.50 (A) Electrodes Permitted for Grounding. (3) Concrete-Encased Electrode. A concrete-encased electrode shall consist of at least 6.0 m (20 ft) of either (1) or (2):

(1) One or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (1∕2 in.) in diameter, installed in one continuous 6.0 m (20 ft) length, or if in multiple pieces connected together by the usual steel tie wires, exothermic welding, welding, or other effective means to create a 6.0 m (20 ft) or greater length; or

(2) Bare copper conductor not smaller than 4 AWG
Metallic components shall be encased by at least 50 mm (2 in.) of concrete and shall be located horizontally within that portion of a concrete foundation or footing that is in direct contact with the earth or within vertical foundations or structural components or members that are in direct contact with the earth. If multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.
Informational Note: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in “direct contact” with the earth.

250.50 (A)-(2) Wold apparently exempt the pool from being bonded if there where more than one CEE present, that is not our case as the system ground is a traditional rod type electrode, and no other connected CEE exists, the home does not have an Ufer ground, only ground rod electrodes and well casings, which are bonded as per NEC Section 250. Additionally, in my estimation, this exception is assuming that the additional CEEs are not incidentally bonded via an equipment grounding connection as is the case with the pool's EP grid, but this is my take and not addressed in the code.

One more thing of note, the equipment grounding connections of the pool equipment do not satisfy the bonding requirements of an electrode system if required, while they do provide a conductive path between the EPG and the EGC, this connection does not comply with NEC's definition of a system bonding jumper.

tim5055 said:
Well, I also think you are Over-thinking it a bit, but if you want to lear more - here is the guy to listen to

You said you read some of his stuff, but here are his classes on the pool.
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Mike Holt's videos are an outstanding resource, I viewed the ones posted, and others, several times before authoring my original post, I was unable to find a reference to this specific question in the free videos, articles and white papers published by Mike Holt.

I originally wanted to post this question on Mike Holt's forum, but the rules over there limit participation to electricians and industry professionals, I am neither of those things.

I appreciate all the comments thus far, and I would like to clarify that I am not asserting anything, I am asking, attempting to learn the facts and am in no way suggesting I'm right, chances are I'm not, I would like to know for sure. I am also in no way suggesting things should be one way or another, I am seeking comprehension of the rules and best practices, nothing more. Please remember I am asking in the context of my own home and pool, I am not a pool professional or otherwise involved in the trade.

I also don't see the harm in bonding the pool shell to the system ground, while it may be impractical after construction, during the build it's not likely to pose a significant challenge, and would not dictate the location of the pool in relation to the service entrance, it would merely require a compliant jumper to be installed between the two.

My interim conclusion, barring further research, is that a bonding jumper between the pool shell and the system grounding electrode, whether required or not, is a good 'best practice' and at minimum can cause no harm, and would meet code, provided the connection is made in accordance with NEC 250.

I appreciate everyones comments, thank you!
 
If it were a "best practice" I think it would be addressed in the NEC. As it is, they don't worry about it enough to address it even stating as you posted "shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes."

If you feel more comfortable, do it.
 
The NEC contains a list of electrodes that must be used where present. All of the grounding electrodes described at 250.52(A)(1) through (A)(7) shall be bonded together to form this grounding electrode system (see Figure 4). In the 2017 NEC, clarification was brought forward by CMP-5 that this did not include the steel reinforcement of an in-ground permanently installed swimming pool.

Members of Code Making Panel-5 (CMP-5) determined that it was never the intent of the NEC to use a pool bonding grid as a grounding electrode.

In this case, the authorities and experts from CMP-5 received a public input(s) asking for clarification to the connection of the structural steel of in-ground permanently installed swimming pools as part of the grounding electrode system. Their conclusion was that this should not be done, thus resulting in another item that is not to be used as part of the grounding electrode system.

By making a connection in this fashion, this would make the swimming pool (and possibly its users) a “super-target” for any stray currents or ground-fault current introduced on this grounding electrode system. This could potentially introduce safety hazards to the occupants of the pool during events such as lightning strike-induced stray currents.

https://iaeimagazine.org/magazine/2018/03/06/in-ground-conductive-pool-shells-for-swimming-pools/
Click to expand...

The NEC specifically says that the bonding grid is not required to be connected to the main ground.
 

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tim5055 said:
If it were a "best practice" I think it would be addressed in the NEC.

If you feel more comfortable, do it.
Click to expand...

While I see your logic, I tend to disagree, there are occasions where best practices are not detailed in regulatory documents.

tim5055 said:
"shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes."

If you feel more comfortable, do it.
Click to expand...

One of my gripes with the how the NEC addresses this issue is the ambiguity of 680.26. All I can glean form the incongruence of 680.26 vs. 250.50 is, not all pool shells and/or EP grids meet the criteria of a CEE, so 680.26 does not establish the requirement, however, those pool shells and EP grids that do meet the criteria for a CEE as set fort in 250.50, are required to be bonded to the ground electrode system.

Again I am not certain of my interpretation, but I am convinced 680.26 does not exempt the pool shell from the CEE requirements found in 250.50, and in my experience, when two regulations overlap, the more restrictive code applies.
 
An 8 AWG or larger solid copper bonding conductor provided to reduce voltage gradients in the pool area shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes.
Click to expand...

In my opinion, this makes it very clear that the NEC specifically exempts the pool bonding grid from any requirement to connect it to the ground electrode.

The wording is "shall not be required". There's no ambiguity about it.

I would not connect it because it could potentially attract fault currents originating elsewhere towards the pool.
 
JamesW said:
In my opinion, this makes it very clear that the NEC specifically exempts the pool bonding grid from any requirement to connect it to the ground electrode.

The wording is "shall not be required". There's no ambiguity about it.

I would not connect it because it could potentially attract fault currents originating elsewhere towards the pool.
Click to expand...

Thank you James!

While I maintain that the reference in 860.26 is ambiguous, not requiring and prohibiting are two different things, the recent amendment to 250.50 is not.

250.50 (B)-(3)
(B) Not Permitted for Use as Grounding Electrodes. The following systems and materials shall not be used as grounding electrodes:
(1) Metal underground gas piping systems
(2) Aluminum
(3) The structures and structural reinforcing steel described in 680.26(B)(1) and (B)(2)

I guess I am not the only one who is confused by this issue.

Thanks again for all the replies, TFP has proven to be an outstanding resource!

EDIT: After researching 250.50 (B)-(3) a bit further, I am not convinced it prohibits bonding the EPG to the system ground, but rather only prohibits using the pool's EPG as part of the REQUIRED grounding electrodes.
 
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Did someone mention overthinking!?! ;) That's my specialty!

I couldn't properly bond my equipment on my pad without also creating a direct path from the bond wire to the main panel ground, through a substantially heavy gauge wire (more than 8). It's inherent in the way everything is grounded to the sub panel's chassis, to which the bond wire is connected via a bond lug. My bond wire is grounded, in multiple places, and there is no other option...

So even if you decided you didn't want to connect your bond to the primary ground, how would you accomplish that?
 
https://iaeimagazine.org/magazine/2018/03/06/in-ground-conductive-pool-shells-for-swimming-pools/

The above reference helps clarify. The main points are that the pool bonding grid and rebar cannot be used as a grounding electrode and that the bonding grid is excluded from the requirements to connect to the grounding electrode.

The bonding grid is going to be connected to the primary grounding electrode via multiple EGCs (Equipment Grounding Conductors). That's unavoidable. You can connect further if you want, but I don't think that I would.

The bonding grid does constitute a grounding electrode but it cannot be used as such.

For safety, the primary grounding electrode should be sufficient for the installation so that the pool bonding grid does not become the default grounding electrode.
 
The pool is a grounding electrode, whether you jumper it to the primary electrode or not is immaterial, at best it changes the impedance of that path to ground. While using it as the primary ground has definite disadvantages, and as such is prohibited by the NEC (2017 change), it's still part of the ground electrode system, no two ways about it.

I still believe there is more to this than is clearly explained in the NEC and the article James posted above, but I am certainly not qualified to expand on it!

I am dubious of the suggestion made in the IAEI article, that putting a #6 wire to a grounding rod (as opposed to whatever the cumulative grounding effect of all the equipment grounds is, plus the massive water filled CEE six feet in the ground) somehow turns the pool into a "supper target".

By the way, I asked two licensed electricians and an inspector this question, they all responded with "it's not required, but you can do it if you want, up to you" so yea, this is clear as mud...

I am very curious as to what the impedance to ground is of the pool as compared our system grounding electrodes, I am going to see if I can have that value measured accurately, I have a hunch the difference is trivial, it would not surprise me if it met the 25 ohm standard, if it did, then this discussion is somewhat moot.
 
One more observation, one that in large part contributed to my original post, all our pool equipment, and by consequence of the EGC, our entire electrical installation has multiple paths to ground, is that not widely regarded as a no no? The whole idea of bonding the EPG to the grounding electrode system was to eliminate the potential for multiple paths to ground with different potentials, which I was always lead to believe was a dangerous condition.

Food for thought.
 
I'm not sure how a slight difference in impedance is going to cause a human harm. It might be measurable, but so what? Same goes for any combo of the differences between the bond wire and ground and earth. Ideally it would all be zero, but because of the age and nature of the connections, and different types of contact to earth, and length of the various wires, and who-knows-what-all-else, some difference in impedance(s) is inevitable, and unavoidable, right? But as long as the difference in electrical potential is always negligible, with or without a fault in the works, then a human can't be harmed by touching two different components at the same time. The ground is providing one type of protection, the bond is providing another. Both important. They each do their own specific job whether they are connected together or not. Which, I'd have to guess, is why there is no need to connect them, or make sure they are not connected, or even tailer, somehow, how they are connected. None of that matters. If the bonding is done correctly, you won't get a shock while reaching for your ladder. If the grounding is done correctly, you won't get a shock from some malfunctioning piece of equipment, etc. Connecting the two systems, or disconnecting them (not that you could do that), shouldn't alter now they each work, as long as they are each built correctly (to code).

I'm just thinking out loud. I don't have any real knowledge of the finer points, I'm just fascinated by this topic ever since I discovered that my "electrician" (aka unqualified pool guy) left off several bond connections. I'm guessing he assumed that the components were already grounded, so why bother (I'm not guessing that he was just lazy about it.). So pardon me while I continue to learn about this stuff by interrupting those who know more about it than I do!! ;)
 
The primary path to ground is the EGC (equipment grounding conductor). As long as this is done correctly to code, it should be sufficient.

I think that if you were going to connect the bonding grid to the grounding electrode, you would want to do it in a way that the grid was connected equally everywhere.

For example, if you had a big 100' x 100' copper mat and you wanted to connect it to the grounding electrode, you would run a bonding jumper from each corner of the mat so that you don't generate a potential difference based on the impedance of the mat.

In any case, it shows the importance of the code. Because electricity is so complicated, it's easy to miss important details even if you understand electricity.
 
Dirk,

I'm not the person to listen to when it comes to electricity and how these systems operate, but I will share my limited understanding in hopes of better explaining what brought about this thread in the first place.

Electricity wants to flow from the point of origin back to the point of origin, not necessarily to the earth, the EGC, as James says, is the primary fault path, but not to ground necessarily, but rather back to the point of origin, yes they are interconnected at the service entrance, but the EGC exists to trip the over current protection device and de-energize the circuit in the event of a fault by carrying the current back to its origin. Only the over current device can de-energize the circuit and eliminate the hazard, simply connecting the fault to ground won't eliminate the touch voltage or hazard potential.

The reason you don't want multiple ground electrodes that are not bonded as part of your EGC is that the current would have to travel through the earth to return to the point of origin, the earth is a very poor conductor and the protection device may take considerably longer to trip if it trips at all, this condition could create a danger to persons as well as a fire hazard. A ground rod with a resistance of 25 ohms would not provide an adequate fault current path, the circuit would remain energized because the fault current would only be about 5 amps, this low a current would not trip a 15 amp breaker, but if you touched this circuit (while in contact with ground), you would get shocked. Make sense?

In the specific case we are discussing, a pool's EPG, this is not the issue, and the pool equipment ground is not compromised as it still has a bonded path to the origin through the EGC, the fact it also has an alternate path to ground is irrelevant, in the event of a fault sufficient current will flow through the EGC back to the point of origin and trip the protection device. At least this is how I understand it.

Now in the conditions I refer to above, I am discussing a fault that originated on your electrical system and the current was looking for a place to go, what I am concerned with regarding the pool's EPG is current that originates from outside your electrical system and looks to enter the system through your earth ground electrodes. Examples of this are nearby lightning strikes (not direct hits, all bets are off in that scenario), power line faults, or issues originating in neighboring structures. In this case the ground becomes energized and when the electricity comes to a point in the ground where you have a ground rod it too will become energized and the energy will flow from that electrode through whatever is connected to it to the next point where it contacts the earth. Electricity follows all paths available in inverse proportion to the impedance of the paths, current flows through all available paths simultaneously. The magnitude of the current flowing in each path depends on the voltage and impedance of each path. The lower the impedance of the path, the greater the current, the higher the impedance of the path the lower the current, this is all provided the voltage remains constant. So if you have two electrodes in the earth, the current will flow between them, the purpose of the bonding jumper is to carry as much current as possible directly through the bonding wire and minimize the current that flows through the other connected paths possibly damaging equipment and creating hazards to people and property.

My thought regarding the EPG was that bonding it to the system ground electrode would lessen the magnitude of the current flowing through the equipment via the interconnection of the EPG and the EGC in the event the ground became energized by an external source, not to protect the people in the pool from stay current or to provide an effective path to clear a fault, those two functions are unaffected bu bonding the pool structure to the system ground. This is one of the reasons we bond metal well casings to the earth ground system, it seemed to me the same logic would holt true for the pool, but alas people smarter than me disagree.

The above information should not be regarded as fact, it's nothing more than my limited understanding, relayed here only and alone for the benefit of further discussion.
 

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