Swimming Pool Electrical Defects Expert Witness Paolo (Paul) Benedetti discusses electrical deficiencies.
Bonding it all Together
Swimming pool bonding is frequently confused with grounding. They are two separately different matters.
Grounding - is a direct path from an electrical appliance (light, pump, heater, receptacle, etc,) to earth. This path is provided by a grounding wire inside the appliance cord or supply wiring conduit.
Bonding - is a LOOP designed to connect all metallic components of a swimming pool, so that their potential ground is the same.
Although
grounding and bonding are closely related, they do serve separate
purposes — both of which work together to increase electrical safety.
The Perfect Path
Through no fault of the swimming pool, the hundreds of yards
of damp steel in the shell often present the electricity with a better
ground than is provided by the home’s copper grounding rod or by
reinforcing steel in a building’s foundation (which is called an Ufford
ground).
In a household electrical system, the electricity returning to
the service entrance panel via the neutral conductor returns to the
neutral bar in the cabinet. Only in this cabinet are the neutral and
grounding bar connected to the metal cabinet. Although designed to return to the utility transformer via the neutral conductor, electricity can travel across the metallic cabinet to the
grounding bar and to the grounding rod.
When a watershape is
properly grounded with a wire leading to that grounding bar, it senses
that the steel in the swimming pool offers electricity another path to
earth that may offer less resistance. In this situation, the possibility
exists that, like some people I know, the electricity will take the
easy way out.
If that happens, the electricity travels right through the
grounding conductor that is connected to the pool equipment’s sub-panel.
This electricity flows back to the various electrical components of the
swimming pool (pumps, heaters, lights) via their grounding conductors rather than to the grounding rod.
When and if this flow occurs, the damp steel within a watershape shell may offer the best path to earth. In a properly bonded
swimming pool, in which all metal components are tied together with a
wire that goes back to the electrical panel and from there to ground,
the pool and all its metal components exist on the same electrical
potential and therefore do not provide a path of least resistance to ground, meaning among other things there is no risk of electrocution.
Where the bonding grid is lacking, inadequate or becomes disconnected from the grounding system, however, there can be a significant risk of electrocution.
Let’s assume that the grounding rod adjacent to the service
entrance panel stands in extremely dry soil (poor conductivity), that its connecting
clamp has come loose, conductor severed or has become corroded. If any of that is the case, the
amount of electricity to be discharged into the earth via a pool’s
steel grid may be significant — perhaps even deadly.
Given the possible range of conditions, let’s look at a set of simple scenarios:
>> A swimmer exits a properly bonded swimming pool via
the stairs. He or she grabs the bonded metal railing in stepping from
the pool, and at one moment has one foot in the pool and the other on a
wet concrete pool deck. Although the pool and railing may be energized,
the swimmer feels nothing at all because the pool, deck and railing all
have the same potential ground. This simply means that all of the metal components are offering the electricity an equal path of resistance to the earth.
>> That same swimmer exits a pool where the metal handrail had been installed after the pool was built — without
any bonding protection and without any contact to the reinforcing grid
in either the pool or the deck. As the swimmer exits the water, he or
she places a hand on the railing, has one foot on the deck and has the
other in the pool (or maybe even both feet on the deck). The electricity flow from the pool, through the swimmer & into the earth via the metallic railing. Because the swimmer is a part of the path of the electricity's discharge into the earth - they receive a shock.
Now let’s consider a third scenario:
>> A pool service technician walks up to a leaking pump
on the same pool. Previously, he or she had cut the bonding wire to
repair the motor. In touching the metal case, a fatal shock occurs as
his or her wet feet present the electricity with a path of less
resistance to earth.
Technically, the service professional became the final path of discharge.
Just as the swimmer getting out of the pool using a non-bonded railing
was electrocuted, just as the worker using the circular saw in my
previous article was shocked to death, the technician effectively became the terminal path to ground and suffered a fatal injury.
The Best Bonds
Again, the principle behind bonding is to equalize the path to ground for the electricity.
In the first example of a properly bonded handrail, the
swimmer didn’t feel anything, as the electricity flowed through the
swimmer but traveled back to ground through the pool’s bonding grid.
The swimmer did not provide the final path to earth for the
electricity. As long as people are a protected by provision of a means
for the electricity to “loop back,” they will not be a part of the path to the final point of discharge.
This is why bonding is so important. Section 680 of the National Electric Code
outlines standards for bonding and grounding swimming pools. The
following is not an all-inclusive list, but it covers the most common
items requiring bonding:
>> Reinforcing steel of the swimming pool, equipment pad and pool deck
>> All metallic items greater than four square inches located within 10 feet of the water
>> Metal handrails, ladders, diving boards and slides
>> All electrical components, housings, junction boxes and niches
>> All junction boxes and niches feeding underwater lighting (with both internal and external bonding)
>> All electrical components associated with the
swimming pool (motors, circuit panels, lighting fixtures, transformers,
heaters, blowers)
>> Wrought-iron fences, metal downspouts, deck drains, deck anchors or volleyball poles.
>> For pool that are not surrounded by decks with reinforcing steel (pavers, grass, etc.), a bonding grid of copper or stainless steel mesh must be installed around the perimeter of the pool & spa [NEC Sec. 680.26(B)(2)].
>> Since many pools are being constructed without metal components in contact with the water (light niches, SS hand railings, etc.), the water must also be bonded. If your pool has a heater that is always in the water path, then more than likely the heat exchanger is bonded as well. Otherwise a permanent source of non-corrosive metal to water contact must be provided.
Furthermore, the bonding conductor between a light’s junction box and the interior of the lighting niche may not
be spliced. These internal bonding wires may only be interrupted within
an approved enclosure and upon a grounding/bonding bar. In addition,
bonding conductors may be either stranded/insulated or solid copper
(minimum #8 size) — and redundancy isn’t a bad idea. In Canada, in fact,
two bonding wires are required between the pool and the equipment pad.
If you follow these simple requirements, you’ll go a long way
toward ensuring that people who come into contact with watershape
fixtures and equipment will not become the path of least resistance.
It’s the right thing to do, and it’s relatively easy to accomplish if
you manage your construction operations well.
