Swimming Pools or Natural Body of Water

[Dennis Alwon]

Met a guy who is installing a natural pool. Here is a wiki definition

A natural swimming pool or natural swimming pond (NSP) is a system consisting of a constructed body of water, where the water is contained by an isolating membrane or membranes, in which no chemicals or devices that disinfect or sterilize water are used, and all clarifying and purifying of the water is achieved through biological filters and plants rooted hydroponically in the system.


So there is a hole in the ground with a membrane laid at the bottom and extending over the side for a few feet. He wants the overhang as long as possible. There is no overflow other than when it rains it pours over the top and then onto this membrane. Water is pulled from the bottom of the pool where the plants are located. The water is injected back into the pool about 2' down in the deep end where the swimming occurs.

No chlorine just a sand filter. He was trying to get by and not have any equipotential bonding. I told him, IMO he had to but the equipotential bonding was going to be under the rubber membrane.

So you see where this is going-- how effective do you think the equipotential bonding will be if there is a rubber membrane sitting atop the soil. I told him he still had to have it since, IMO it is a pool as well as a artificial body of water or is it? How does this differ from a pond or lake?

Just thought it was an interesting situation and wondered what you all thought. This is not exactly what it will be but the idea is there.

http://www.inspirationgreen.com/natural-pools-swimming-ponds.html

 

[Dennis Alwon]

I got the pic working

 

[ActionDave]

I'm going with Artificial Body of Water. No one ever said you couldn't swim in a ABW.

 

[Dennis Alwon]

I'm going with Artificial Body of Water. No one ever said you couldn't swim in a ABW.

The one that is going in will not have the overflow as this one has unless there is heavy rains. No chemicals seems to change some things but it is not pertinent in the NEC

 

[Dennis Alwon]

The question is more the equipotential bonding.


This pic is more like it but instead of the deck there will be just that membrane coming over the edge of the pool.

 

[don_resqcapt19]

You will have to bond the equipment and the water. If there is no earth type material on top of the membrane, I would think the perimeter surface would start at the outside edge of the membrane.

 

[kwired]

Forget code for a minute, and ask what is there to produce any voltage potential?

We have similar issue at natural bodies of water - nothing is really there to produce potential until we introduce things like boat docks with power on them. Many electrocutions at boat docks have happened even with GFCI protection because the shock hazard was from things that equipotential bonding grid would help with yet are somewhat impossible to provide at such a large body of water.

I would also show the owner some good examples of what could happen both with and without the equipotential bonding grid and maybe you can make the owner realize just how much this may be worth. Even below a non conductive liner it will still have some effect. With a non conductive liner you are building a huge capacitor, and AC current still flows through a capacitor, DC current only charges and discharges from a capacitor.

 

[Dennis Alwon]

You will have to bond the equipment and the water. If there is no earth type material on top of the membrane, I would think the perimeter surface would start at the outside edge of the membrane.

That is my gut feeling also but then suppose there was a deck with non conductive material - like Trex. The world is changing-- the line between a pool and a pond with aeration has been blurred imo.

 

[kwired]

I think you need to look harder at the definitions in 680 and 682

from 680:

Permanently Installed Decorative Fountains and Reflection
Pools. Those that are constructed in the ground, on the
ground, or in a building in such a manner that the fountain
cannot be readily disassembled for storage, whether or not
served by electrical circuits of any nature. These units are
primarily constructed for their aesthetic value and are not
intended for swimming or wading.


Permanently Installed Swimming, Wading, Immersion,
and Therapeutic Pools. Those that are constructed in the
ground or partially in the ground, and all others capable of
holding water in a depth greater than 1.0 m (42 in.), and all
pools installed inside of a building, regardless of water depth,
whether or not served by electrical circuits of any nature.


Pool. Manufactured or field-constructed equipment designed
to contain water on a permanent or semipermanent basis and
used for swimming, wading, immersion, or therapeutic purposes.


from 682:

Artificially Made Bodies of Water. Bodies of water that
have been constructed or modified to fit some decorative or
commercial purpose such as, but not limited to, aeration
ponds, fish farm ponds, storm retention basins, treatment
ponds, and irrigation (channel) facilities. Water depths may
vary seasonally or be controlled.

I think if it is intended to be used for swimming, wading, immersion or therapeutic purposes - you have a 680 application.

 

[kwired]

I will say that definition of an artificially made body of water may need some tweaking, but would mostly be for large bodies of water. Just look at some of the reservoirs that are at least partially man made that cover thousands or millions of acres, and consider there is a lot of swimming or similar activity in those man made bodies of water, then imagine the task of constructing an equipotential plane throughout the reservoir. Probably not impossible but not all that practical, and very expensive.

 

[Dennis Alwon]

I don't think I need to look harder at the def. I am playing devils advocate a bit. I agree art 680 should be used-- it was just an interesting situation I had not seen. The equipotential bonding I was not certain of-- code requires 18-24" from the inside edge-- IMO, I would install equipotential bonding ring at 18-24 under the membrane and another 18-24" outside the membrane to cover all bases.

 

[Dennis Alwon]

The other thing I noticed about these pools is that they don't seem to have the fence that would be required to keep children out when no one is around.

Kwire- you are saying that the equipotential bonding would work even if it were under the membrane?

 

[mwm1752]

If there is a potential difference from the earth you are standing on with one foot and the water body your other foot is submersed in trouble follows --- bonding the water & having a equipotential plane bond appears to be required.

 

[Dennis Alwon]

If there is a potential difference from the earth you are standing on with one foot and the water body your other foot is submersed in trouble follows --- bonding the water & having a equipotential plane bond appears to be required.

Again I think we all agree that equipotential bonding and bonding the water is required. In the scenario I heard about the water level changes depending on the rain since there is no overflow. I think he is thinking about making an area outside the pool that will drain. If that is the case then the bonding either goes under the membrane, outside the membrane or both- the nec did not have this in mind for pools.

 

[kwired]

Kwire- you are saying that the equipotential bonding would work even if it were under the membrane?

Not saying it is ideal, but will have some function.

If you connected an ungrounded conductor to said grid, I'm pretty certain you would be able to read at least some voltage between the water and a remote ground point, and you would not want to be caught between the pool and the close perimeter if for some reason you did not have that grid extended away from the perimeter

 

[GoldDigger]

....the equipotential bonding would work even if it were under the membrane?

To some extent.
1. If there are gaps in the membrane above water level, then the soil on top of that part of the membrane might end up close to the potential of the soil immediately below it, so in that specific case a bonding grid under the membrane would help to control that potential.
2. The portion of the grid below the membrane would serve as a partial cage to keep any potential gradients under the pool from causing step potentials beyond the boundary of the membrane. On the other hand, if the problem is that water and the rest of the equipotential grid is elevated above remote ground because of limited ground conductance, then the the part of the grid under the membrane will not do anything to limit step potential beyond the edge of the membrane.

 

[PetrosA]

I don't do pools at all, nevertheless, this is an interesting thread. In a regular pool, is the equipotential bonding to protect against faults in the lighting system, pump system or both? If the pump is a factor, would some kind of belt driven pump (which eliminates any possibility of the water becoming energized by a fault in the pump) or a 12V pump eliminate the need to build the equipotential bonding?

 

[GoldDigger]

I don't do pools at all, nevertheless, this is an interesting thread. In a regular pool, is the equipotential bonding to protect against faults in the lighting system, pump system or both? If the pump is a factor, would some kind of belt driven pump (which eliminates any possibility of the water becoming energized by a fault in the pump) or a 12V pump eliminate the need to build the equipotential bonding?

I think that if there is any way for there to be a stray voltage gradient across the footprint of the pool (utility primary fault) or the possibility of water itself being energized, as by a falling overhead wire or even a powered gadget brought into the pool area and energized from a local receptacle or an extension cord, then the need for an equipotential grid is still there.
It would only change what items needed to be bonded.

 

[don_resqcapt19]

The other thing I noticed about these pools is that they don't seem to have the fence that would be required to keep children out when no one is around. ...

Around here the local building code would require the fencing...it is even required for many storm water retention ponds. I think the local code applies if the water can be 2' or deeper.

 

[GoldDigger]

The fence does not have to be close to or even in sight of the pool if access to the entire area that contains the pool is effectively controlled. Unless local regulations affect that.

Tapatalk!