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Old 07-14-2012, 08:43 AM   #16
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danpik, EXCELLENT write up. Thanks.

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Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
Answers based on the 2011 NEC.
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Old 07-14-2012, 09:21 AM   #17
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I concur, that must have taken some time to write, but most helpful to the OP I'm sure!
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Old 07-14-2012, 12:00 PM   #18
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Thanks guys. That writeup was an evolution over several weeks this spring on the pool forum I am on. For some reason it seems like there was an unusually large amount of questions this spring about pool shocks (electrical). There was also a large amount of misinformation about grounding and bonding being thrown out there as well. I usually will not get into the specifics of how to do the bonding on the posters pools as I am not there to see them in person but, instead, do as you have and refer them to read the code on what is required. I wrote the explanation more to clear up the confusion on the difference between the two and the reasons both exist. It still amaizes me that some people think a ground rod stuck in the dirt will protect them. I also have fixed about 20 bonding issues on pools around here this summer due to handyman instalations. I had a toe to toe with one of them a couple of weeks ago about this very thing. I ultimatly blew him in to the code people in town for doing an unpermitted install on a pool.
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Old 07-14-2012, 12:32 PM   #19
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Quote:
Originally Posted by danpik View Post
For some reason it seems like there was an unusually large amount of questions this spring about pool shocks (electrical).
Here's another.
What was the lowest voltage that you had a complaint about? Was it from a man (women and children are more sensitive)?

Thanks.
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Old 06-21-2015, 09:15 AM   #20
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What type of decking material are you using. Stone, pavers, brick, concrete are all cosidered conductive surfaces and need to have a proper bond system installed. Do not move forward with this project untill you have a good understanding of why the bonding system is important and why it exists. I fix about 8-10 pools each year for customers who complain of electrical shocks when getting in and out of the pool, when touching the metal fence around the pool while standing on a wet deck, touching the ladder while standing on the deck, Etc, Etc, Etc.

I am a pool owner and a member of a pool owners forum. This question comes up almost weekly.

I wrote this a while back to help some people with understanding the difference between bonding and grounding......

Bonding and grounding are two often misunderstood concepts.

To start, we will look at grounding first. In the 120 volt electrical supply system for your pool pump there are 3 wires. Hot, Neutral, and ground. The hot and Neutral serve to move power from the source and back to the source so the pump can run. The ground wire in this system serves only as a non resistive conductive path back to source should something happen internally in the pump. For example, if, for some reason, the hot wire came in contact with the motor housing, the housing could become energized. Without the ground present, the housing could sit there waiting to shock any unsuspecting person or animal who happened to touch it. You would be the conductor to ground. Ground being the ground you are standing on. Now, because the resistive properties of the ground you are standing on are too high for the current to short circuit back to the source, it would most likely not trip the overcurrent protection (fuse, breaker). A couple of times here I have referred to "source". This is the power company transformer on the pole out at the street. The hot and neutral connections are both on this transformer and the returning current wants to get back to what is called the center tap on the transformer either via the grounding system or the neutral system. If there is a ground wire present in the circuit, the hot wire coming in contact with the motor housing would immediately trip the overcurrent protection as there would be a dead short in the system.

Bonding. The really mis-understood concept.
Have you ever experienced a static shock?...You know, you shuffle your feet across a carpet in the dry season and touch a metal doorknob. If you were bonded to that doorknob when you shuffled across the floor you would not have felt the shock when you touched it. Everything in the universe has what is referred to as electrical potential. Humans have a certain potential, a piece of steel has its own potential, water its own, etc, etc, etc. Most times this potential is not different enough to feel it. When you shuffle your feet on the carpet though, your potential changes from that of the doorknob. When you get close enough to the doorknob though both you and the doorknob want to get to the same potential. when that happens, a spark jumps the gap and evens out the potential. Fortunately there is little amperage behind it so there is no chance of getting electrocuted and since the event is a one time discharge you just dismis it. Now, lets look at your pool. your pool pump is grounded back to the source thru the ground wire. But, it still is at some level of electrical potential. Your pool water is at some other level of potential, your heater at its own level, heck, the ground you are standing on is at some level of potential. This means that all of the items in the vicinity have some varying degree of electrical potential. Under most circumstances these potentials are so close to each other that you never feel any kind of shock. however, every once in a while something happens to change the potential of one of the items. It could be a stray voltage induced from an underground electrical service, It could be a slight resistive leakage of current in your pumping system. What ever it is there is a potential difference. Now imagine you are getting out of the pool and as you touch the metal side of the pool you get the shock of your life. Hopefully not enough to kill you but a good shot none-the-less. Guess what? You just became the bonding conductor in the system. Had all of the components in the system been bonded together by the #8 bonding wire you never would have felt it. The wire is a non-resistive path between all of the components and since electricity is lazy, it will take the least resistive path. This bonding system will also protect you if you were standing on the ground and decided to touch the water to see how warm it is. If the bond is in place there would be no potential difference between the water and the ground even if there were a stray current floating around.

Hopefully this helps clear some of this up
Many thanks to you for posting such an informative and well written explanation of an often misunderstood concept. Thanks for taking the time to do so.
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Old 06-22-2015, 12:53 PM   #21
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You mean bonded.
by nec verbiage, yes. but the last step which is not a requirement is to take that bonding to the gnd stakes and service gnd. so by verbiage, if its all "gnd'd" then such grounding makes a bonding grid.
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Old 06-22-2015, 08:25 PM   #22
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by nec verbiage, yes. but the last step which is not a requirement is to take that bonding to the gnd stakes and service gnd. so by verbiage, if its all "gnd'd" then such grounding makes a bonding grid.
I have no idea what you are suggesting...
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Old 06-23-2015, 09:41 PM   #23
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I have no idea what you are suggesting...
1) if the potential in center of pool is 1kv for just a 2x2 area but its only 0.001v at the edge, and the pool is 100% correctly done in bonding grid, what does the bonding do for that potential issue thats in center of pool?
2) salt water = ions, you are not likely to get shocked in a salt water pool where the railings are in the water (wire bonded or not).
3) if you "GND" everything (pool water, metal, decking), we know there's a diff between GND and Bonding by their definitions, but if its all GND'd then its all at same GND potential, therefore a conclusion is made, its also all equipotential bonded and the potential is not an unknown, we expect it to be close to zero. thus, stray current from a branch gfi that enters the "bonded/gnd'd" connection should trip the gfi.

i cant really dumb it down any more than that.

Last edited by concrete_joe; 06-23-2015 at 09:46 PM.
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Old 06-24-2015, 05:31 AM   #24
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IMO, you are overthinking why we bond swimming pools.
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Old 06-24-2015, 05:38 AM   #25
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You realize when we bond a swimming pool, we are not trying to bring the voltage to zero, but mask the voltage already existing. So let's say the grounded conductor from the utility company is 4 volts, since we bond our grounding conductors to the grounded conductor, the equipment grounding conductor at the pool motor is now 4 volts, so when we bond everyone at the pool that is metal we are actually energizing everything at 4 volts. This is how bonding works, we are just masking the problem, because it's impossible to remove it.
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Old 06-24-2015, 05:48 AM   #26
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Quote:
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The wire is a non-resistive path between all of the components and since electricity is lazy, it will take the least resistive path.
It is a great write-up, but the above is not strictly correct. Current takes all paths between point A and point B in its effort to complete a circuit. The current does split (current divider circuit from basic electrical theory) in proportion to the resistance of each path relative to the total resistance. In your example of bonding, there is some (very small) current flowing thru the human, but you are correct that the bonding wire takes MOST of the current.

I mention this because equipotential bonding is very effective at 120V. When you start getting into higher distribution voltages (above 20 kV) and transmission voltages, injuries can still occur, even with equipotential bonding in place. Bonding is still the safest bet, but injury is possible.

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Old 06-24-2015, 06:12 AM   #27
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thus, stray current from a branch gfi that enters the "bonded/gnd'd" connection should trip the gfi.
The GFCI will trip with or without a bonding grid. The "stray" voltage will cause an imbalance in the circuit that will cause the GFCI to trip. Bonding and grounding have nothing to do with a GFCI

Last edited by danpik; 06-24-2015 at 06:18 AM.
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Old 06-24-2015, 06:17 AM   #28
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Quote:
Originally Posted by busman View Post
It is a great write-up, but the above is not strictly correct. Current takes all paths between point A and point B in its effort to complete a circuit. The current does split (current divider circuit from basic electrical theory) in proportion to the resistance of each path relative to the total resistance. In your example of bonding, there is some (very small) current flowing thru the human, but you are correct that the bonding wire takes MOST of the current.

I mention this because equipotential bonding is very effective at 120V. When you start getting into higher distribution voltages (above 20 kV) and transmission voltages, injuries can still occur, even with equipotential bonding in place. Bonding is still the safest bet, but injury is possible.

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I do agree with you 100% on the "least resistance" part. I may have to change the wording in that. Since most laypeople think that way I mistakenly wrote it that way. It probably should have been expressed differently.
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Old 06-24-2015, 06:18 AM   #29
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Quote:
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1) if the potential in center of pool is 1kv for just a 2x2 area but its only 0.001v at the edge, and the pool is 100% correctly done in bonding grid, what does the bonding do for that potential issue thats in center of pool?
You'd have to have some pretty long arms to reach from the middle of the pool to the edge... I'm not sure how your scenario would exist in the real world.





Quote:
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2) salt water = ions, you are not likely to get shocked in a salt water pool where the railings are in the water (wire bonded or not).
You should make this proposal in the next NEC.... see how that works out for you.



Quote:
Originally Posted by concrete_joe View Post
3) if you "GND" everything (pool water, metal, decking), we know there's a diff between GND and Bonding by their definitions, but if its all GND'd then its all at same GND potential, therefore a conclusion is made, its also all equipotential bonded and the potential is not an unknown, we expect it to be close to zero. thus, stray current from a branch gfi that enters the "bonded/gnd'd" connection should trip the gfi.

i cant really dumb it down any more than that.
Bonding does not bring the voltage to zero, it brings everything to an equal value, whatever that value maybe....
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Old 06-24-2015, 09:37 AM   #30
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we are just masking the problem, because it's impossible to remove it.
or is it??


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