You also have to consider if something away from the pool is energized. In that case, current would be more likely to flow towards the pool if you have a big bonding jumper between the bonding grid and the grounding electrode.
Opinions On Bonding Pool's Equipotential Grid Directly To System Ground Electrode
- Thread starter Hanstb
- Start date
The EGC already does that, I fail to see how the net result would vary by any significant amount, what would vary greatly is the amplitude of the current flowing through the equipment. All roads lead to Rome, all we are discussing is how much traffic there is on each road, the current will make it to the pool either way.
The pool EPG is not isolated, never could be as long as the equipment is bonded to it, all we are doing by bonding the EPG to the system ground is proportioning the current flow and diverting some of it away from the equipment, pool gets energized either way.
Thank you James,
Referring to my posts as knowledge may be overly generous, but I appreciate it none the less.
It does not address the principal question being discussed in this thread, but for those of you that may want to learn more about equipotential bonding as it relates to swimming pools, this is a very well authored report from the NFPA:
Evaluation of "Alternate Equipotential Bonding Means" to Reduce Voltage Gradients In Pool Areas
Referring to my posts as knowledge may be overly generous, but I appreciate it none the less.
It does not address the principal question being discussed in this thread, but for those of you that may want to learn more about equipotential bonding as it relates to swimming pools, this is a very well authored report from the NFPA:
Evaluation of "Alternate Equipotential Bonding Means" to Reduce Voltage Gradients In Pool Areas
- Nov 12, 2017
- 11,972
- Pool Size
- 12300
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
I will pit my limited understanding against yours! Together we will create an even greater limited understanding!! 
I can't speak knowledgeably to every purpose of the residential ground system, nor to how multiple grounds might increase the level of danger to humans. Only what I've pieced together from my own logic. I'm not even sure what a ground rod is doing for the system. The ground wire is connected to the neutral wire in the main breaker box, and both can deliver the current back to the original source (the neutral of the incoming mains), to complete the circuit. The ground typically does so only when a fault occurs and the hot wire comes in contact with a grounded surface, like the case of some appliance (GFCIs have significantly reduced even that purpose). I've assumed this provides a better path for the electricity than a human standing on the dirt, or otherwise electrically connected to the earth or a grounded surface. I've always assumed that ground rods had more to do with lightning than anything else, but I'm only guessing there. I suppose they are connecting the surrounding earth to the main's neutral wire. So that anything a human can touch, or stand on, has no voltage potential to that of the neutral wire or grounded item.
What I understand about bonding is that it doesn't matter what the grounds are doing, or if they even exist at all, or if they are damaged, or if they've been electrically charged somehow. Or how much voltage is applied to the pool or its equipment, from any source, ground(s) or otherwise. By bonding all the components of a pool and its surrounding area (every item a human can connect with his body), you eliminate the voltage difference (potential) between all the items, and therefore any possibility that a dangerous amount of current can traverse through the flesh. It doesn't matter if the voltage of the items are 1V higher than some other point across the yard, or down the street, or 1000V, as long as the voltage difference between the two touched items is zero (which is achieved by the bond wire). Much like a bird can sit on a high voltage line, there is no path to any other items within reach that are of a different voltage (I'm probably not using the correct terms.), so the bird is safe. So even if your pool got charged somehow, from a local leak or from down the block, and you were in it, the current from the water would not travel through you to the ladder or the concrete deck, because there is already a much easier path for it to take, an 8G copper wire. Now whether that wire was connected to a ground wire, in one or more places, or to the breaker box, or the pole down the street, it wouldn't matter, because the difference in voltage between the two things you can physically attach yourself to is 0. Now if the items weren't bonded with a single, uninterrupted 8G wire, and relied on each being connected to the earth through a ground rod or to the neutral wire through some other various means, then you could have a problem. Because significant voltage differences could exist between two items with only a few feet between them (like if one was wet, and the other wasn't, or the items were of a different material). So then your impedance mismatch would matter greatly. And a lighting strike down the street would matter, as the voltage traveling through the dirt or other conduits could enter the various components at different voltage levels. Enough to harm a person, for sure. But not so when the bond wire is properly installed.
Are you worried that if one end of your bonding grid is connected to ground in one way, and another end is not grounded, or grounded in a different way, and then you are somehow able to connect yourself between those two ends, that you'll get a shock? I suppose there could be a voltage potential there, however far fetched the logistics of that event might be, but it's still got a big ol' copper wire between the two ends that is going to take the brunt of the current before it ever harmed you. Technically, your body would still pass some amount of current, because you are a conductive path connected in parallel with the bond wire. But basic electrical math (calculating amps through each of two or more resistors connected in parallel) would reveal the current through you would be virtually undetectable by you, and certainly in no way harmful. The voltage applied to you would only be caused by the resistance of the 8G copper wire running between the two items you can reach (infinitesimal, which is why they spec 8G), not how the two opposite ends were grounded, nor the resistance between the grounds attributed to the dirt between them. Actually, to be accurate, the dirt would also be a path, also in parallel with you and the bond wire, and would actually reduce the current running through you. No matter, the bond wire would be the path that would most affect the current through the flesh, not the dirt. And that current will be very close to zero.
As James has pointed out many times in this forum, the complexities of electricity are far beyond the scope of this forum, and certainly far beyond my understanding of them. So buyer beware. This is what electricians are for!!
And, as James has alluded to, if yours was a real concern, there would be a code to address it. Some percentage of building codes exist because someone, somewhere, somehow, got hurt or killed. Many codes exist to protect against very unlikely possibilities. So if it's of any comfort, however twisted, if there isn't a code for it, nobody has ever been significantly hurt because of it, and won't ever likely be. (Completely skewed and unfounded logic!) Someone got hurt in a pool, they came up with bonding (NOT grounding) as the preventative solution, and coded the heck out of it to make sure it got done correctly. Since (as I understand it) grounding doesn't help or hurt the protection the bonding is providing, there was no need to include any more about it than they did in the code that addresses bonding. (That's my own conclusion.)
I can't speak knowledgeably to every purpose of the residential ground system, nor to how multiple grounds might increase the level of danger to humans. Only what I've pieced together from my own logic. I'm not even sure what a ground rod is doing for the system. The ground wire is connected to the neutral wire in the main breaker box, and both can deliver the current back to the original source (the neutral of the incoming mains), to complete the circuit. The ground typically does so only when a fault occurs and the hot wire comes in contact with a grounded surface, like the case of some appliance (GFCIs have significantly reduced even that purpose). I've assumed this provides a better path for the electricity than a human standing on the dirt, or otherwise electrically connected to the earth or a grounded surface. I've always assumed that ground rods had more to do with lightning than anything else, but I'm only guessing there. I suppose they are connecting the surrounding earth to the main's neutral wire. So that anything a human can touch, or stand on, has no voltage potential to that of the neutral wire or grounded item.
What I understand about bonding is that it doesn't matter what the grounds are doing, or if they even exist at all, or if they are damaged, or if they've been electrically charged somehow. Or how much voltage is applied to the pool or its equipment, from any source, ground(s) or otherwise. By bonding all the components of a pool and its surrounding area (every item a human can connect with his body), you eliminate the voltage difference (potential) between all the items, and therefore any possibility that a dangerous amount of current can traverse through the flesh. It doesn't matter if the voltage of the items are 1V higher than some other point across the yard, or down the street, or 1000V, as long as the voltage difference between the two touched items is zero (which is achieved by the bond wire). Much like a bird can sit on a high voltage line, there is no path to any other items within reach that are of a different voltage (I'm probably not using the correct terms.), so the bird is safe. So even if your pool got charged somehow, from a local leak or from down the block, and you were in it, the current from the water would not travel through you to the ladder or the concrete deck, because there is already a much easier path for it to take, an 8G copper wire. Now whether that wire was connected to a ground wire, in one or more places, or to the breaker box, or the pole down the street, it wouldn't matter, because the difference in voltage between the two things you can physically attach yourself to is 0. Now if the items weren't bonded with a single, uninterrupted 8G wire, and relied on each being connected to the earth through a ground rod or to the neutral wire through some other various means, then you could have a problem. Because significant voltage differences could exist between two items with only a few feet between them (like if one was wet, and the other wasn't, or the items were of a different material). So then your impedance mismatch would matter greatly. And a lighting strike down the street would matter, as the voltage traveling through the dirt or other conduits could enter the various components at different voltage levels. Enough to harm a person, for sure. But not so when the bond wire is properly installed.
Are you worried that if one end of your bonding grid is connected to ground in one way, and another end is not grounded, or grounded in a different way, and then you are somehow able to connect yourself between those two ends, that you'll get a shock? I suppose there could be a voltage potential there, however far fetched the logistics of that event might be, but it's still got a big ol' copper wire between the two ends that is going to take the brunt of the current before it ever harmed you. Technically, your body would still pass some amount of current, because you are a conductive path connected in parallel with the bond wire. But basic electrical math (calculating amps through each of two or more resistors connected in parallel) would reveal the current through you would be virtually undetectable by you, and certainly in no way harmful. The voltage applied to you would only be caused by the resistance of the 8G copper wire running between the two items you can reach (infinitesimal, which is why they spec 8G), not how the two opposite ends were grounded, nor the resistance between the grounds attributed to the dirt between them. Actually, to be accurate, the dirt would also be a path, also in parallel with you and the bond wire, and would actually reduce the current running through you. No matter, the bond wire would be the path that would most affect the current through the flesh, not the dirt. And that current will be very close to zero.
As James has pointed out many times in this forum, the complexities of electricity are far beyond the scope of this forum, and certainly far beyond my understanding of them. So buyer beware. This is what electricians are for!!
And, as James has alluded to, if yours was a real concern, there would be a code to address it. Some percentage of building codes exist because someone, somewhere, somehow, got hurt or killed. Many codes exist to protect against very unlikely possibilities. So if it's of any comfort, however twisted, if there isn't a code for it, nobody has ever been significantly hurt because of it, and won't ever likely be. (Completely skewed and unfounded logic!) Someone got hurt in a pool, they came up with bonding (NOT grounding) as the preventative solution, and coded the heck out of it to make sure it got done correctly. Since (as I understand it) grounding doesn't help or hurt the protection the bonding is providing, there was no need to include any more about it than they did in the code that addresses bonding. (That's my own conclusion.)
One argument that can be made in favor of connecting the bonding grid to the grounding electrode is that it could provide a redundant path to ground if the original equipment grounding conductor is damaged or removed.
For example, in this thread
Rust from pool light ground wire
a pool service company wanted to remove a bonding jumper that connected the metal light niche forming shell to the light junction box.
The purpose of the bonding jumper is to provide a supplemental ground path in addition to the ground wire in the light cord.
Since the metal light niche forming shell is bonded to the equipotential bonding grid via the external bonding lug, it could provide a backup path to ground if the bonding grid is connected to the grounding electrode.
The service company said that they routinely remove the bonding/grounding jumper.
Even if the bonding/grounding jumper is removed, the light cord still contains a ground. So, the ground path is not completely defeated but it's less than required and it demonstrates one way a ground path can be compromised.
Overall, I don't know that I would connect the bonding grid to the grounding electrode but I don't think that I would necessarily disagree with someone who did.
For example, in this thread
Rust from pool light ground wire
a pool service company wanted to remove a bonding jumper that connected the metal light niche forming shell to the light junction box.
The purpose of the bonding jumper is to provide a supplemental ground path in addition to the ground wire in the light cord.
Since the metal light niche forming shell is bonded to the equipotential bonding grid via the external bonding lug, it could provide a backup path to ground if the bonding grid is connected to the grounding electrode.
The service company said that they routinely remove the bonding/grounding jumper.
Even if the bonding/grounding jumper is removed, the light cord still contains a ground. So, the ground path is not completely defeated but it's less than required and it demonstrates one way a ground path can be compromised.
Overall, I don't know that I would connect the bonding grid to the grounding electrode but I don't think that I would necessarily disagree with someone who did.
- Nov 12, 2017
- 11,972
- Pool Size
- 12300
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
I was just thinking about a damaged bond wire, and there is redundant backup for that, too. To some degree, the ground wires are back ups, if less effective ones. The two components that I discovered were not bonded, were all connected by grounds, so they were technically on the bonding grid, which was attached to the same grounding system elsewhere (just not with a sufficient gauge wire). The big loop itself also adds some redundancy, I think. I don't know if that was the primary intention of the circle of wire traversing the entire perimeter of the pool, but it seems to me the circle is like running two wires to everything. If the wire becomes severed between, say, the ladder and the light, they would each still be connected to the grid, because the wire is connected to each component from both directions. Now I'm sure the wire branches off to a single wire in many places, like back to the pad, for example, but at least around the pool, where the bigger risk of shock exists, there is some redundancy provided by the circle.
The main purpose of a ground rod in a residential electrical service is to provide a path in the event of a high voltage surge such as that from an electrical storm. A ground rod will not clear a fault(trip a breaker) in the event of a short circuit in an appliance. The groundedconductor (ie: neutral) is there to provide the zero volt reference to do that. This is one of the reasons the only connection between your grounding circuits in your home and the neutral can only be connected at the first disconnect in the service (main panel). Any other neutral/ground connections can put neutral current on the ground wire too. Connecting the bonding grid of a pool to the grounding system is not specifically prohibited in the NEC. In fact, a properly wired system may have a connection already if the pump or heater and other components connected to the bonding grid are also grounded as they use the same metal structure of the component for the connection points.
Dan
Dan
I have researched this topic a bit further since my last post, but have been unable to locate a definitive answer, I have strong doubts that 250.50 (B)-(3) prohibits bonding the pool grid to the system ground, and may only prohibit using the pool's EPG as part of the required system grounding electrodes, but of course, that is not definitive either. It seems the more I read the more confusing this becomes.
250.50 (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)
Informational Note: See 250.104(B) for bonding requirements of gas piping.
The informational note attached to 250.50 (B) is of interest, while 250.50 (B) (1) prohibits the use of a metal underground gas pipe as a grounding electrode, 250.104 (B) requires that the metal underground gas pipe be bonded!
250.104 (B) Other Metal Piping. If installed in or attached to a build‐ ing or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to any of the following:
So it would seem 250.50 (B) was not intended to prohibit bonding, it only prohibits the use of those structures and/or components as part of the required system grounding electrodes.
I was surprised by the lack of consensus amongst members of the Mike Holt Code Forum reading this very issue, and some of the individuals posting on those threads are purported to be members of the code making panels that contribute to the NEC, including one engineer that specifically states he is a member of Code Making Panel-5. I don't know if linking to a post on another forum is an acceptable practice, and I don't want to draw the ire of the moderators, but if you are interested that forum has numerous posts dealing with this very question, you will find dissenting opinions on this whole issue. (The forum rules over there do not allow non industry personnel to post, or I would have posted my question there.)
I found one post particularly interesting, the OP talks about a pool installation where the system grounding electrode is within 5 feet of the pool and as such required to be bonded to the EPG as per NEC 680.26 (B) (7), that spurred an interesting discussion.
I would like to clear up a possible misunderstanding about my original question and the intent of bonding the EPG to the system grounding electrode, after which I will refrain from making any additional attempts to clarify this topic as I am not in any way qualified to do so, and I do not frequent the Holliday Inn.
I was only concerned with providing additional equipment protection from voltage surges, while not negatively impacting safety of life. I am not trying to make the pool safer for swimmers, I was only asking if bonding the pool to the grounding electrode system would provide additional protection for the pool equipment in the event of a nearby lightning strike or other event that would energize the pool shell, without diminishing the EPG's ability to perform it's primary function nor introducing a potential risk to swimmers.
It's clear to me that our pool is up to code as it was built, and is safe for swimmers. I am not seeking to make any DIY modifications to my electrical installation, however, I would have hired an electrician to install the bonding jumper, and may still, if I had been able to quantify the benefit, for now there does not seem to be a consensus, and opinions are all over the map. By the way, my electrician is willing to do it, and our AHJ is willing to sign off on the installation, so go figure...
Thank you once again to those of you who replied, while this topic may lie outside of the scope of this forum, there are undoubtably members who are subject matter experts in the NEC and have been involved with every aspect of pool construction and residential electrical installations.
Best regards to All
250.50 (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)
Informational Note: See 250.104(B) for bonding requirements of gas piping.
The informational note attached to 250.50 (B) is of interest, while 250.50 (B) (1) prohibits the use of a metal underground gas pipe as a grounding electrode, 250.104 (B) requires that the metal underground gas pipe be bonded!
250.104 (B) Other Metal Piping. If installed in or attached to a build‐ ing or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to any of the following:
So it would seem 250.50 (B) was not intended to prohibit bonding, it only prohibits the use of those structures and/or components as part of the required system grounding electrodes.
I was surprised by the lack of consensus amongst members of the Mike Holt Code Forum reading this very issue, and some of the individuals posting on those threads are purported to be members of the code making panels that contribute to the NEC, including one engineer that specifically states he is a member of Code Making Panel-5. I don't know if linking to a post on another forum is an acceptable practice, and I don't want to draw the ire of the moderators, but if you are interested that forum has numerous posts dealing with this very question, you will find dissenting opinions on this whole issue. (The forum rules over there do not allow non industry personnel to post, or I would have posted my question there.)
I found one post particularly interesting, the OP talks about a pool installation where the system grounding electrode is within 5 feet of the pool and as such required to be bonded to the EPG as per NEC 680.26 (B) (7), that spurred an interesting discussion.
I would like to clear up a possible misunderstanding about my original question and the intent of bonding the EPG to the system grounding electrode, after which I will refrain from making any additional attempts to clarify this topic as I am not in any way qualified to do so, and I do not frequent the Holliday Inn.
I was only concerned with providing additional equipment protection from voltage surges, while not negatively impacting safety of life. I am not trying to make the pool safer for swimmers, I was only asking if bonding the pool to the grounding electrode system would provide additional protection for the pool equipment in the event of a nearby lightning strike or other event that would energize the pool shell, without diminishing the EPG's ability to perform it's primary function nor introducing a potential risk to swimmers.
It's clear to me that our pool is up to code as it was built, and is safe for swimmers. I am not seeking to make any DIY modifications to my electrical installation, however, I would have hired an electrician to install the bonding jumper, and may still, if I had been able to quantify the benefit, for now there does not seem to be a consensus, and opinions are all over the map. By the way, my electrician is willing to do it, and our AHJ is willing to sign off on the installation, so go figure...
Thank you once again to those of you who replied, while this topic may lie outside of the scope of this forum, there are undoubtably members who are subject matter experts in the NEC and have been involved with every aspect of pool construction and residential electrical installations.
Best regards to All
In one of my code classes I took a while back this was brought up. The intent of this was to dis-allow the use of the gas pipe as THE grounding electrode. Years ago, many electricians used the gas and water piping as a grounding electrode instead of driving a rod. The reason the code was added primarily is that most gas piping underground is or is being converted to plastic and thus would provide no ground. Also, since the meter serves as the bonding connection between the house and the underground piping, there is the possibility of gas and sparks mixing when a meter is disconnected. There is some push to dis-allow the use of water piping for the same reason. In fact, several years ago a water tech in my town was seriously hurt when he was pulling a water meter. There was no bonding jumper in place and when he broke the connection he became the current path for the homes electrical system. It was later discovered that the neutral to the street was compromised and the homes neutral path was using the water pipe to get back to the neutral connection on the pole via the neighbors house.
Dan
- Nov 12, 2017
- 11,972
- Pool Size
- 12300
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
A note about one of the purposes of the equipment grounding conductor.
There are 3 wires coming from the service transformer. 2 hot and 1 neutral (center tap). The neutral is grounded at the transformer. The neutral is also grounded at the home.
Because the neutral is grounded at the transformer and the home, the ground between the transformer and the home becomes a parallel path for the current that is intended to travel through the neutral.
As long as the neutral is sufficient, the current traveling through the ground should be small. If the neutral is compromised, the current going from the home to the transformer through the ground can increase significantly.
If a power wire in an appliance contacts the metal case of the appliance, the case becomes charged. If a person touches the case and is grounded, current can flow through the person into the ground and back to the grounded neutral at the home.
One of the purposes of the equipment grounding conductor is to provide a low impedance path from the equipment to the homes main neutral so that a power to casing fault creates enough current to trip the breaker.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html
There are 3 wires coming from the service transformer. 2 hot and 1 neutral (center tap). The neutral is grounded at the transformer. The neutral is also grounded at the home.
Because the neutral is grounded at the transformer and the home, the ground between the transformer and the home becomes a parallel path for the current that is intended to travel through the neutral.
As long as the neutral is sufficient, the current traveling through the ground should be small. If the neutral is compromised, the current going from the home to the transformer through the ground can increase significantly.
If a power wire in an appliance contacts the metal case of the appliance, the case becomes charged. If a person touches the case and is grounded, current can flow through the person into the ground and back to the grounded neutral at the home.
One of the purposes of the equipment grounding conductor is to provide a low impedance path from the equipment to the homes main neutral so that a power to casing fault creates enough current to trip the breaker.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html
- Nov 12, 2017
- 11,972
- Pool Size
- 12300
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
Thanks James. That was all clear in my head, though I'm sure I didn't express it well enough in my posts. The vocabulary is part of my challenge. I appreciate being able to describe what I think I know about any given topic here at TFP, and either get that confirmed or corrected. I hope that in this thread that was clear, that my posts here were less about informing anyone about anything, but rather checking that my growing understanding about grounding and bonding and their differences and purposes is on the right path.
I suspect the intent of 250.50 (B) (3) is also to preclude the use of the pool shell as THE primary grounding electrode, and not to prohibit the bonding of the pool to the ground electrode system.
I continue to look for an ironclad answer, if I find it, I will update this post.