Explaining electricity and swimming pools
By Consolidated Manufacturing International
Proper grounding and bonding around a swimming pool are critical because water conducts electricity. There are multiple grounding and bonding mistakes pool professionals commonly make when constructing a pool. Here’s how to avoid them: The first error usually encountered is not knowing the difference between grounding and bonding. Bonding is connecting metallic objects together. From a technical perspective, this keeps all metal at the same potential voltage, so without a difference in potential voltage, you have no current flow and will not get shocked. This is how a bird on a powerline does not get shocked. Grounding is providing an electrical path to the earth, like “bonding” to the earth, and an excess electric charge will disperse instead of building up and creating a potential hazard.
There are two general types of pool shells, Conductive pool shells like Gunite/Shotcrete/Concrete, and Non-Conductive pool shells like Fiberglass or Vinyl Liner. A common mistake is that pools need to be grounded and not bonded, when in reality, as stated by a utility industry expert, a conductive shell pool is the world’s best ground rod. The National Electrical Code, published by the National Fire Protection Agency (NFPA), requires all metal objects within 5 feet of the water to be bonded together, such as ladders, handrails, and metal light niches. This is referred to as equipotential bonding, and there is a difference between equipotential bonding (keeping all metal objects at equal potential voltage) and creating an equipotential plane.
When metal objects are bonded as mentioned, they are connected together, which ensures the objects stay at the same potential voltage. All the metal in the pool area, including the rebar reinforcement of a gunite pool, is all bonded together with a #8 solid copper wire and usually attached to the pump motor. The pump is powered from an electrical panel with circuit breakers, and that electrical panel is of course connected to the electric utility company’s distribution system, which includes the neutral wire. Therefore, whatever voltage is on the utility system neutral is now on the pool system. Think of the pool system altogether floating in the air at various heights. The various heights represent the various voltages on the pool. However, as long as you stand on the “platform” you won’t fall off and get hurt. It’s the same with standing on a pool system that is energized — as long as you stand in the water or on a bonded deck, you won’t “step off” onto a different potential voltage, make an electrical path connection, and get hurt. If that bird sitting on a wire were to be heavy enough to make it sag to the ground and touch the earth, which is at a different potential voltage, that bird will make a connection and a current will flow, hurting or killing that bird.
A fiberglass or vinyl liner pool protects the water from stray voltage in the ground. A gunite pool is conductive and exposes the swimmer to stray voltage in the ground. However, the rebar reinforcement of the gunite creates an equipotential plane around the body of water that protects the swimmer from this stray voltage, as it can’t pass through the equipotential plane.
Years ago, rebar was used in the concrete decks that extend the equipotential plane from around the body of water to underneath the deck. However, lots of builders now use fiber reinforced concrete, which is strong enough for a person to walk on without reinforcement. Pavers are also popular and have no need for steel reinforcing. Beware, this can be very dangerous because there is no equipotential grid in the deck to protect the swimmer who is now standing dripping wet, with one foot on the protected pool system and one foot off. All utility industry experts weighing in on the matter — including EPRI, IEEE, and NEETRAC — recommend a steel or copper grid in or under the deck to provide this protection. Again, this grid extends the equipotential plane from around the pool to a few feet out, increasing the size of the “platform”.
Creating an equipotential plane is often confused with equipotential bonding of all metal in the pool area using the #8 bond wire attaching the objects. It is important to understand that they are two separate issues, and both must be done. This will result in a very safe pool environment that is healthy and can be enjoyed for many years.