Saturday, November 30, 2013

Swimming Pool Bonding Grid

Gounding and Bonding ARE NOT the same thing!

I frequently hear the incorrect statement that "grounding and bonding are the same thing."  Though closely related and even interconnected, they are not the same thing.

Purpose of Bonding

Bonding is installed to ensure that every metallic component of a swimming pool has the same electrical impedance - that is, the same resistance to electricity.  The impedance of a bonding grid should be ZERO.


Redundancy exists in many components attached to a bonding grid, to ensure that the impedance is exactly the same for all attached components.

A case study:
A large pool contained numerous light fixtures housed in PVC niches and connected to PVC conduit.  

Every niche had a bonding wire connecting it's exterior bonding lug to the reinforcing steel in the shotcrete.  

None of the niches had the required interior bonding wire installed.

The impedance reading of all of the niches varied between 250 and 500 ohms, except for one.  That one niche had 0 ohms of resistance.  Why?

The bonding wire from the equipment pad was connected to the clamp on the reinforcing steel, then continued down to the bonding lug on the back of that one niche.  Yes, it also happened to be the niche closest to the equipment pad.

Though all of the other niches were connected to the bonding grid, the concrete and steel created resistance between those niches and the one niche with the "home-run" bonding wire.

The purpose of the internal insulated green #8 bonding wire, is to provide another path to ensure that the impedance is and remains at -ZERO- .

Fatal Path to Ground

All of the grounding wires at a property are interconnected.  At the service entrance (electrical meter), there is a grounding rod.  It's purpose, is to discharge any stray voltage. 

However, the grounding rod may not always present the best source of ground for electricity.  The hundreds of yards of wet steel and concrete in the backyard may actually be a better ground.... so electricity takes the path of least resistance & discharges itself into the earth through the shell of the swimming pool.  Though the water may in fact be energized, a proper bonding grid keeps it all safe.

Now, along comes a swimmer.  They touch a metallic part of the swimming that is properly bonded back to the pool steel & bonding grid.  Though the swimmer is a part of the "loop" they do not feel anything - because the electricity is not discharged into the earth (it loops back).

Now, the swimmer touches a metallic component that is not properly bonded or has a high impedance.  The swimmer is now in the direct path of the electricity as it discharges into the earth through the metallic component.  The swimmer is shocked - maybe even fatally.  Why?  They are in the path to ground for the electricity.

When there is a loop and the impedance is zero, humans are not affected.  But, when the human being is a part of the circuit as the electricity is discharged into the earth - they are shocked.

Simply stated:  The purpose of a bonding grid is to ensure that all of the components have the same potential (impedance) to ground.

Contact the author, Paolo Benedetti of Aquatic Technology Pool and Spa at: or 408-776-8220. 
 Visit his website at: 
All Contents © Aquatic Technology Pool & Spa, 2013. 
All rights reserved.

Sunday, November 24, 2013

ACI 318-11 thicker stronger shotcrete pools

ACI 318-11 requires that the shotcrete walls on salt water pool be increased in strength and thickness.  Shotcrete is defined as either the wet or dry process of pneumatically placing concrete.

ACI - The American Concrete Institute

ACI is the definitive expert on concrete.  So much so, that they publish a myriad of standards that relate to concrete and it's use.

ACI Standard 318-11, "Building Code Requirements for Structural Concrete" has been directly incorporated into the International Building Code (adopted by 48 States, except Minnesota) and by the California Building Code.  This effectively makes it the law of the land. 

ACI 318-11 changes the requirements

ACI 318-11 redefined the parameters of the required coverage of concrete required over the reinforcing steel.  Prior versions of ACI 318 were ambiguous as to what was actually defined as sulfate or corrosive conditions.

ACI 318-11 establishes the additional shotcrete protection required when exposed to defined levels of sulfates, water containing chlorides (salts) and permeability.

ACI 318-11, Table 4.2.1 indicates that shotcrete swimming pools are required to meet the criteria for Permeability - P1 (condition defined as: "in contact with water where low permeability is required") AND Corrosion Resistance - C2 ( a condition defined as: "concrete exposed to moisture and an external source of chlorides from
deicing chemicals, salt, brackish water, seawater, or spray from these sources").

The resulting P1 and C2 classifications require specific mix design ratios (ACI 318-11, Table 4.3.1).

ACI 318-11, Table 4.3.1, P1 classification sets a maximum water to cement ratio (w/cm2) of 0.50 and a MINIMUM 28 day compressive strength (f'c) of 4,000 PSI.  While the C2 classification establishes a maximum water to cement ratio (w/cm2) of 0.40 and a MINIMUM 28 day compressive strength (f'c) of 5,000 PSI.

Therefore, any swimming pool that is going to be treated with sodium compounds is REQUIRED to have a maximum water to cement ratio (w/cm2) of 0.40 and a designed compressive strength (f'c) of 5,000 PSI.  Sodium compounds utilized in swimming pool sanitization include sodium chloride (chlorine), sodium bromide (bromine) or sodium (salt-electrolysis chlorination).

The C2 classification (Table 4.3.1) further specifies that the requirements of ACI 318-11, 7.7.6 "Corrosive Environments" be met.  Section 7.7.6 states that the coverage over reinforcing steel shall not be less than 2 inches for walls and slabs subject to such corrosive environments.

Structural Engineers & Building Departments

Many structural engineers and building departments do not abide by the requirements of ACI 318-11.  They either attempt to justify design criteria less than the standards, are not versed on the most up to date requirements or simply fail to comply with the codes.

When there is an issue of structural integrity on your pool, the most recently adopted version of the IBC, CBC or ACI standards will apply in court, whether or not they were enforced by the engineer or building inspector.

Do you want to be left hanging with a structural engineer who will have to defend his decision to design a structure that was below the requirements of the building codes?  
Do you want to take the risk that he will be able to convince a jury of lay people that a weaker structure is acceptable?

I thought not!

Contact the author, Paolo Benedetti of Aquatic Technology Pool and Spa at: or 408-776-8220. 
Visit his website at: 
All Contents © Aquatic Technology Pool & Spa, 2013. 
All rights reserved.