Question about equipotential bonding & grounding

[michaelkingdom]

I'm a home inspector learning about equipotential bonding of the pool area. My question is, how is the equipotential bonding system at the pool area tied into the main grounding system?

I understand that all metal objects near the pool need to be bonded so that if a metal component becomes energized the voltage is dissipated over the equipotential plane. What I don't understand is how that energy makes its way back to the house's grounding system and back to the ground rod. Are they connected somewhere (maybe at a ground at the pool electrical shut off switch?) Or does the pool's rebar act as an independent ground?

 

[Dennis Alwon]

The equipotential bonding ties eerything together and ends at the bonding lug on the pool motor. That is it's only connection back to the wiring system. The purpose of the equipotential bonding is to keep any gradient voltages at the same potential

 

[don_resqcapt19]

I'm a home inspector learning about equipotential bonding of the pool area. My question is, how is the equipotential bonding system at the pool area tied into the main grounding system?

I understand that all metal objects near the pool need to be bonded so that if a metal component becomes energized the voltage is dissipated over the equipotential plane. What I don't understand is how that energy makes its way back to the house's grounding system and back to the ground rod. Are they connected somewhere (maybe at a ground at the pool electrical shut off switch?) Or does the pool's rebar act as an independent ground?

Energy does not want to get back to a ground rod. It wants to get back to its source.

The pool bonding is not about energy going somewhere...it is about keeping everything in the pool area at the same voltage so there there are no potential differences from any one conductive object in the pool area to any other conductive object in the pool area.

 

[iwire]

The bonding grid has nothing to do with sending energy back to the panel.

It's only purpose as Dennis said is to keep everything at the pool at the same potential.

The only connection back to the panel will be the EGCs for any of the bonded pool equipment.

 

[roger]

As the others have said, the equipotential bonding is not for grounding or fault clearing, it is for equipotential. Think of it this way, if everything in this equipotential area that you can touch is charged at 120 volts from the same leg of the service and you are in contact with it, you would be fine.

Roger

 

[michaelkingdom]

So if a bonded pool light housing or bonded pool pump became energized would the equipotential plane ideally dilute the strength of that current to make it non-lethal to swim? Or does the equipotential plane just make everything energized so that one could swim in an energized pool and not know it?

 

[Dennis Alwon]

So if a bonded pool light housing or bonded pool pump became energized would the equipotential plane ideally dilute the strength of that current to make it non-lethal to swim? Or does the equipotential plane just make everything energized so that one could swim in an energized pool and not know it?

The pool light and pump have an equipment grounding conductor that will trip the breaker so that the frame of the motor or light do not get energized

 

[don_resqcapt19]

So if a bonded pool light housing or bonded pool pump became energized would the equipotential plane ideally dilute the strength of that current to make it non-lethal to swim? Or does the equipotential plane just make everything energized so that one could swim in an energized pool and not know it?

That is what it is intended to do, but as Dennis said, the EGC should clear a fault like that.

 

[michaelkingdom]

That is what it is intended to do, but as Dennis said, the EGC should clear a fault like that.

Okay, I think I am understanding. The breakers for the pool light, pump and heater serve as the overcurrent devices. Faulty or failing wiring will trip the breakers.

The equipotential grid is designed so that there are no voltage differences between metal objects and the pool water so the human has "bird on a wire" protection from stray voltages.

Extreme question: So even in the case where the pool was energized by a downed SEC would there still be "bird on a wire" protection?

 

[mpoulton]

So if the pool is energized but is not drawing enough amps to trip the 20 amp breaker, the human can swim in an energized pool with the "bird on the wire" effect?

Yes. In order for this to happen, the equipment grounding conductor path from the pool equipment (pump, lights, heater, etc.) back to the service would have to be interrupted somewhere. That is one of the situations the equipotential bonding grid is intended to protect against, by making it safe to swim (technically - good luck getting me in that pool!) even if there is a fault somewhere that energizes part of the pool or causes current flow through the earth in the pool area.

 

[don_resqcapt19]

....
Extreme question: So even in the case where the pool was energized by a downed SEC would there still be "bird on a wire" protection?

It would depend on the amount of current that is flowing....the current flow create voltage drop and so not everything is still at the same potential.

 

[michaelkingdom]

the current flow create voltage drop and so not everything is still at the same potential.

If you would not mind elaborating on this it would be appreciated. Voltage drop?

 

[MD84]

If you would not mind elaborating on this it would be appreciated. Voltage drop?

Use ohms law here. A current flowing through a resistance generates a voltage. All conductors have a resistance as well as the resistance of connections.

 

[iwire]

If you would not mind elaborating on this it would be appreciated. Voltage drop?

Whenever you have current flowing on a conductor there is voltage drop or loss due to resistance. So during a fault the potential voltage at one end of the conductor will be different from the other.

The amount of drop is directly related to the amount of current flowing (along with other factors) during a short circuit the current spikes, in a normal 20 amp branch circuit the short circuit current could be 50-75-100 amps or more for the time it takes the breaker or fuse to open the circuit. During that time the high current will cause a large voltage drop and as result a larger difference of potential.

 

[MD84]

I think of voltage drop as a design issue. Voltage is being dropped from the supply voltage.

I think of exposure voltage as a safety issue. The voltage potential to ground is raised.

 

[don_resqcapt19]

I think of voltage drop as a design issue. Voltage is being dropped from the supply voltage.

I think of exposure voltage as a safety issue. The voltage potential to ground is raised.

Yes, it is raised by the voltage drop on the fault return path.