Quote:
Originally Posted by
Rich L 
Heavy power lines overhead and normal power lines carrying current and running along with other leads for a distance can have voltages induced.
An electrician working on aircraft elevators had a problem with the elevators operating improperly. He found a sencing wire with 20 volts on it. He was really confused when he laid a cable along the ground and it also showed a significant voltage without being connected to anything.
I had him ground both ends of the sencing lead and the voltage disappeared. The lead was in the cable way of some heavy power runs and the voltage fluctuated with the current in the power runs. Grounding the sheath caused the voltages to go to ground and not impact the sencing leads.
The pond won't be protected if the gunnite is coated with an insulating barrier such as fiberglass, polyurea or any directly applied coating that provides an insulation coating between the gunnite and the water. Grounding the rebar is proper but most cement and gunnite in-ground ponds are well grounded by the extensive contact between the pond material and the earth.
There are two conditions in our ponds. One is in a pond where the water is isolated from earth(ungrounded) where the pond has an insulation coating between the water and ground potential The other is grounded where the pond water is well grounded by using metal components or other products that will conduct electricity. Isolated water won't conduct to ground and touhing a hot lead and the water won't produce a shock. However it will be at ground level if a fixture leaks so the water reaches a component that's grounded. This could be a light fixture of an electrical heater up in the filter room or even the makeup water when the ponds filling and the metalic line of the makeup plumbing is close enough to the pond water for the water to conduct into the filter water. If insulating layers of pond coatings delaminate, the pond is likely grounded.
All this depende on the amount of salts(TDS) in the water. Folks with snow runnoff won't have the same problem as those who use well water.
The best solution is to positively ground the pond water. Pond water won't cunduct current well so a ground in a remote filter room won't provide the same protection in the pond as a good conducter close to potential voltage sources. The ground must be good enough that a gfci will trip when a ground fault is created by current into the pond strong enough to cause harm to people.