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

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: info@aquatictechnology.com or 408-776-8220. 
 Visit his website at: www.aquatictechnology.com. 
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