pool bonding @12 feet height

Status
Not open for further replies.
J

jvf

Member
Location
Maui
Occupation
electrician
Hello,
Tried to search the forums for a possible explanation of bonding height requirements but couldn’t find any. As the resident electrician, I’m reviewing pool bonding for a contractor friend. I happened to watch the Mike Holt video where he expresses bewilderment (my sentiment as well) about the requirement to bond items such as metal roof flashing within the 5/12 limit but WAY up in the air that no one could ever touch. Can anyone provide a real world example of a pool related electrical injury that has happened because of someone touching a non-bonded roof flashing or metal deck railing 10 or 11 feet off the pool deck and 4 feet away from the edge (no diving boards installed for anyone to launch themselves, either)? Alternately, can anyone propose a scenario of how such an injury could actually occur? For that matter, how can someone get hurt if the window or slider frame isn’t bonded either?
Thanks,

jvf
 
Dennis Alwon said:
My guess is the distance was figured based on the length of the pool hand leaf skimmer. IDK.... I doubt you will find an example but what I said may help understand why it is there.
Click to expand...

Who knows, but that’s a great guess. With my vacuum/skimmer pole, I’ve bumped my flashing and metal gutter for my roof many times on accident not realizing how long the dang thing is. It’s probably 10’ and 10’ from the pool edge too. So 5/12 is easily attainable.
 
Thanks for responding guys,

That IS a great guess. I suppose the thing to do would be to find and contact the authors of this portion of the code to see how scrambled their brains were (or how desperate they were to appear to be “doing something” to “improve” the code book). But, it is another example of the hopelessness of the situation. As I watched Mike’s video during the portion explaining that ag buildings were among the areas that needed serious consideration of an equipotential plane all I could think of was that, at some point, the cows were going to be straddling the earth and the equipotential plane at the same time. Then what? Sure enough, later he explained that in order to deal with this the concept of an equipotentail “gradient” was introduced with the bonding grid diving into the earth in an attempt to gradually bring the animals onto the equipotential gradient area.

Now, here we are at the pool. At some point, someone is going to bridge the great divide and straddle the fence. Imagine that your precious 10 yr. old daughter has just gotten out of the shower and walked barefoot across the damp concrete deck above the pool to see who is in the water. As she grabs the bonded handrail to look over the scene, she is now likely grounded and will be shocked accordingly if conditions allow. So, who shall we energize, the pool guy for a moment or our daughter? I vote for the pool guy. Based on size, he will have a better chance of “getting loose” if things are really amiss so I’d prefer not to purposely energize the handrail. Mike further gave the example of the dish guy getting shocked on the roof while investigating why the set top boxes kept frying. Talk about unintended consequences. NASCAR, and the racing community in general, seems to do a much better job at avoiding the unintended consequences of a safety improvement possibly because their response is an attempt to fix a real situation that caused someone serious harm. Back in the day when the good ole USA still had a manufacturing base I ran our test and development lab and managed all the UL, CSA, etc. files. During product development we had an engineer that would stay up at night imagining all the things that could or might go wrong and try to devise preemptive schemes and “fixes”. One was more likely to have been struck by lightning 3 times in one day and survived than to have encountered the vast majority of his paranoid meanderings. In a similar vein, I think it’s more likely that many of these code changes are coming about in the same way. Someone imagined that the pool guy might touch the handrail with the skimmer basket handle. “O no!” we have to do something about that! And, off we go down the rabbit hole. So again, I ask, has anyone actually been hurt because of lack of bonding in this situation?

But, maybe I’m old and all ate up. Either way, we’ll give up and follow Mike’s advice: “If it’s in the code-just do it”.

Thanks,

jvf
 
jvf said:
Thanks for responding guys,

That IS a great guess. I suppose the thing to do would be to find and contact the authors of this portion of the code to see how scrambled their brains were (or how desperate they were to appear to be “doing something” to “improve” the code book). But, it is another example of the hopelessness of the situation. As I watched Mike’s video during the portion explaining that ag buildings were among the areas that needed serious consideration of an equipotential plane all I could think of was that, at some point, the cows were going to be straddling the earth and the equipotential plane at the same time. Then what? Sure enough, later he explained that in order to deal with this the concept of an equipotentail “gradient” was introduced with the bonding grid diving into the earth in an attempt to gradually bring the animals onto the equipotential gradient area.

Now, here we are at the pool. At some point, someone is going to bridge the great divide and straddle the fence. Imagine that your precious 10 yr. old daughter has just gotten out of the shower and walked barefoot across the damp concrete deck above the pool to see who is in the water. As she grabs the bonded handrail to look over the scene, she is now likely grounded and will be shocked accordingly if conditions allow. So, who shall we energize, the pool guy for a moment or our daughter? I vote for the pool guy. Based on size, he will have a better chance of “getting loose” if things are really amiss so I’d prefer not to purposely energize the handrail. Mike further gave the example of the dish guy getting shocked on the roof while investigating why the set top boxes kept frying. Talk about unintended consequences. NASCAR, and the racing community in general, seems to do a much better job at avoiding the unintended consequences of a safety improvement possibly because their response is an attempt to fix a real situation that caused someone serious harm. Back in the day when the good ole USA still had a manufacturing base I ran our test and development lab and managed all the UL, CSA, etc. files. During product development we had an engineer that would stay up at night imagining all the things that could or might go wrong and try to devise preemptive schemes and “fixes”. One was more likely to have been struck by lightning 3 times in one day and survived than to have encountered the vast majority of his paranoid meanderings. In a similar vein, I think it’s more likely that many of these code changes are coming about in the same way. Someone imagined that the pool guy might touch the handrail with the skimmer basket handle. “O no!” we have to do something about that! And, off we go down the rabbit hole. So again, I ask, has anyone actually been hurt because of lack of bonding in this situation?

But, maybe I’m old and all ate up. Either way, we’ll give up and follow Mike’s advice: “If it’s in the code-just do it”.

Thanks,

jvf
Click to expand...
If you can find the year a change was made and then look up the proposal (or public input more recent years) as well as the reports on those proposals by the CMP's you will know what the CMP was thinking when the change was made.

As far as livestock and the gradual incline at boundaries, you have to remember a cow has four legs and much longer "wheel base" than humans do, so therefore they are exposed to a wider zone than humans typically are just standing there on the ground.

The pool - as you get farther away from the water the risks to lessen, as you are in much more vulnerable situation when immersed in the water then when standing on even wet ground. But you mentioned the 10 yr old walking across the pool deck and grabbing the hand rail. If this is a hand rail within close distance to pool then it and the deck are supposed to be bonded and will be same potential.

A perimeter fence away from the pool could bring more risk, but pretty much about same risk as same type of fence around a baseball field or something similar. That is still a much reduced risk compared to being immersed or partially immersed in the water when you make contact.
 
bwat said:
Who knows, but that’s a great guess. With my vacuum/skimmer pole, I’ve bumped my flashing and metal gutter for my roof many times on accident not realizing how long the dang thing is. It’s probably 10’ and 10’ from the pool edge too. So 5/12 is easily attainable.
Click to expand...

My pool house is 8’ away and 10’ to the gutter. I hit it all the time with my pole.
I’m pretty sure the gutter isn’t bonded.
 
Hi kwired,

The deck that the girl will walk across is not the pool deck which we will of course bond for good reasons. She will be on the 2nd floor deck of the house which overlooks the pool. So, in the "where does it all end?" scenario, to follow the code's logic one would also have to bond the deck above where the handrail resides. Or, not bond the handrail in the first place. If we are to believe Mike's presentation, one person has already been hurt by touching bonded roof flashing and getting shocked. But, I'm still waiting to hear a report of anyone at pool level getting shocked because something far above their heads that they will never be able to reach was NOT bonded.

jvf
 
jvf said:
Hi kwired,

The deck that the girl will walk across is not the pool deck which we will of course bond for good reasons. She will be on the 2nd floor deck of the house which overlooks the pool. So, in the "where does it all end?" scenario, to follow the code's logic one would also have to bond the deck above where the handrail resides. Or, not bond the handrail in the first place. If we are to believe Mike's presentation, one person has already been hurt by touching bonded roof flashing and getting shocked. But, I'm still waiting to hear a report of anyone at pool level getting shocked because something far above their heads that they will never be able to reach was NOT bonded.

jvf
Click to expand...
Only way for that to happen is to have another object within that person's reach that is not at same potential.

If deck is conductive material but for some reason electrically isolated from rail, that might happen. Otherwise there would need to be some other conductive object that is at a different potential and the person would have to touch it and rail at same time.

About only somewhat ordinary way to get shocked by an object far above when standing at pool level would be as mentioned earlier in this thread - using a long handled skimmer or vacuum pole that is conductive.
 
I agree that the potentials must be different but until I have a full set of plans I still have concerns that it could happen. In Mike’s presentation he went to the guy’s house and felt for himself the consequences of touching the unbonded deck surface while touching the bonded pool water. So, if we are required to bond the handrail and it happens to be isolated from a grounded, conductive deck then someone nowhere near the pool could get shocked. Are Mike and I the only ones that think it’s ridiculous to purposely energize a previously un-energized part of a building far removed from the pool thus potentially (no pun intended) causing a shock hazard that did not exist before? What am I missing here? I would honestly like to find a realistic presentation of just what dangerous situation this requirement mitigates based on field reports of shock incidents and a desire to eliminate some real danger in spite of causing another. This structure is being built in California. Fortunately, again according to Mike, most of California utilities mitigate this neutral to ground voltage by using “double bushing” transformers (what ever that means electrically so I’m interested in learning more about it). Therefore, I’m gambling that there will be no real danger in our case but still……
 
jvf said:
Are Mike and I the only ones that think it’s ridiculous to purposely energize a previously un-energized part of a building far removed from the pool thus potentially (no pun intended) causing a shock hazard that did not exist before?
Click to expand...
The concept of this is manifest in the rule that EGCs shall not interconnect grounding receptacles on an ungrounded circuit.
 
jvf said:
I agree that the potentials must be different but until I have a full set of plans I still have concerns that it could happen. In Mike’s presentation he went to the guy’s house and felt for himself the consequences of touching the unbonded deck surface while touching the bonded pool water. So, if we are required to bond the handrail and it happens to be isolated from a grounded, conductive deck then someone nowhere near the pool could get shocked. Are Mike and I the only ones that think it’s ridiculous to purposely energize a previously un-energized part of a building far removed from the pool thus potentially (no pun intended) causing a shock hazard that did not exist before? What am I missing here? I would honestly like to find a realistic presentation of just what dangerous situation this requirement mitigates based on field reports of shock incidents and a desire to eliminate some real danger in spite of causing another. This structure is being built in California. Fortunately, again according to Mike, most of California utilities mitigate this neutral to ground voltage by using “double bushing” transformers (what ever that means electrically so I’m interested in learning more about it). Therefore, I’m gambling that there will be no real danger in our case but still……
Click to expand...
Same thing can happen when there is no pool at all. No bonding of a conductive deck surface and introduce any object connected to an equipment grounding conductor in one way or another. The shock potential is enhanced near a pool and is biggest risk for someone immersed/partially immersed in the pool.

Double bushing transformer basically means the primary does not utilize MGN and needs full voltage insulated bushings on both input leads because it is fed with two ungrounded conductors. Use of this means there is no current on a grounded neutral, which is also bonded to the secondary neutral.

A major problem with MGN is rise in voltage on the neutral over true earth because of voltage drop on the neutral, that neutral is bonded to all the secondary grounded conductors, if you don't bond them together you are likely to have a voltage between them.

I think most POCO's use MGN and mostly line to neutral transformers. In order to eliminate all possibility of voltage rise on the neutral you about have to not use any transformers that connect to the neutral other than for bonding/grounding purposes. If you went with all two bushing transformers but then added one here or there that does use neutral, you just introduced current to the neutral and there will be voltage drop on that neutral if there is current on it.
 
Thank You,

That was a perfect explanation of a double bushing transformer. Hopefully Mike is correct and SCE uses them. This property actually has a transformer vault at the top of our hill. We ran conduit down to their 15k (I believe) vault near the road and they planted the 240v step down transformer next to our meter panels. I’ll call them at some point to see what they used. As I’ve been thinking about all this I started to realize just what you pointed out: because of the distribution system, ANYTHING securely connected to equipment ground is subject to having a voltage potential with respect to earth ground. What a bizarre situation. But, except for certain scenarios-like swimming pools-practical experience shows that there is little real danger. Which is why I think a handrail 4,1/2 feet back and 11.1/2 feet up from the pool edge presents no danger to anyone remotely near the pool and shouldn’t need to be bonded because of other problems that could cause. During my 20+ years in manufacturing I won many battles during the product approval process with UL as I argued against provisions in our Standard that I felt were ridiculous or physically impossible to occur. But, I’m not about to take on an NEC committee over this (although there are several other issues that I’d also like to discuss with them) so we’ll keep our heads down and just worry about making the inspector happy.

jvf
 
jvf said:
Thank You,

That was a perfect explanation of a double bushing transformer. Hopefully Mike is correct and SCE uses them. This property actually has a transformer vault at the top of our hill. We ran conduit down to their 15k (I believe) vault near the road and they planted the 240v step down transformer next to our meter panels. I’ll call them at some point to see what they used. As I’ve been thinking about all this I started to realize just what you pointed out: because of the distribution system, ANYTHING securely connected to equipment ground is subject to having a voltage potential with respect to earth ground. What a bizarre situation. But, except for certain scenarios-like swimming pools-practical experience shows that there is little real danger. Which is why I think a handrail 4,1/2 feet back and 11.1/2 feet up from the pool edge presents no danger to anyone remotely near the pool and shouldn’t need to be bonded because of other problems that could cause. During my 20+ years in manufacturing I won many battles during the product approval process with UL as I argued against provisions in our Standard that I felt were ridiculous or physically impossible to occur. But, I’m not about to take on an NEC committee over this (although there are several other issues that I’d also like to discuss with them) so we’ll keep our heads down and just worry about making the inspector happy.

jvf
Click to expand...
It is not a problem with properly bonded pools, other than possibly at the boundary like you are concerned about, but at the pool edge is still much higher risk.

Where it is a problem is at marina's, docks, etc. where it is not practical to install equipotential bonding for the entire body of water like it is for a pool, and we usually talk about a couple incidents (almost always a death involved) at these kinds of places at least once or twice a year on this site. Haven't heard any stories yet this year though.

Your underground conduit for the transformer primary? what size conduit did you run? If only 2 inch or even 2.5 inch probably has medium volt cable with center ungrounded and concentric grounded conductor and is operating line to neutral. It would not be large enough to pull multiple ungrounded conductors of that voltage rating.
 
Yes,

I remember reading about horrible accidents happening at marinas occasionally and it’s terrible. We’re pondering how to bond our concrete pool deck surface. As reinforcement, in lieu of rebar, construction calls for corrugated metal sheets (I believe my contractor friend said they used to be called W sheets) and a 6*6 mesh grid with #10 wire (too small to connect to if #8 is minimum size for anything). The sheets aren’t very wide and he thinks they get spot welded (or something) together on site so at least it’s contiguous (I’d hate to think about bonding a few dozen separate sheets). Hopefully, this system is used around pools enough to have bonding hardware readily available (we’re good at finding hardware). But if not, how to connect the bond wire? I asked him to see if acceptable lugs could be welded to the sheet at various points around the pool to bond to the pool shell but, not being a very good welder, I’m not sure if dissimilar metals can be welded together. Possibly we could drill through and clamp a terminal with washers and bolts being careful of material used. If none of this is practical (or acceptable to the inspector) I suppose the backup will be the old “run the copper wire around the pool” idea and bond to it. Knowing my friend, he might do that anyway. No one will ever be able to accuse us of under building.

Edison had us run a 4” conduit down the hill which we dutifully mandreled while pulling in the mule tape (the crews know us well enough to trust us) but I didn’t pay much attention to what they pulled in. We have a 400A meter and a 200A ag meter.

P.S. In case I’ve misled anyone by using the wrong nomenclature, our rapidly fading from this discussion stainless steel handrail should have been referred to as the deck railing itself. The bottom of any given post is what will be almost 12’ up. If we do have to bond this beast, we’ll have to figure how to bury the bond wire in a nearby column or something. Running it up the wall outside to get to the roof flashing like someone did in Mike’s presentation ain’t gonna cut it on this building.



jvf
 
Status
Not open for further replies.
Top