Shocking Voltage at Unfinished Swimming Pool

Lake Norman, North Carolina, USA

Background

A homeowner was concerned about the safety of her children and husband when their swimming pool was under construction. She indicated that they were getting shocked with they pulled dirt in to fill in the sides of the pool while standing in the pool water. The concrete deck was not poured at that time. The swimming pool site under construction was 4 to 6 inches larger than the fiberglass pool shell. This gap had to be filled in with dirt before the concrete deck was poured.

Possible Causes

The initial investigation considered several possibilities:

• Faulty wiring on the customer side.
• Open current-limited fuse at a capacitor bank.
• Open or damaged system neutral.

Action Taken

The possible cause were ruled out by:

• Temporarily de-energizing the owner's wiring by pulling the power meter.
• Measuring the load and source capacitor current.
• Inspecting the system neutral because the area where the owner's home was located is subject to tree-related damage.

The next step in the investigation was to measure the shocking voltage and to check for proper bonding at the swimming pool. The shocking voltage was measured at 3.1 VAC from the pool's water to the soil area around the pool. The swimming pool's components (pump, handrail, ladder, coping stone, and so on) were properly bonded.

The customer was informed that the shocking voltage would be at equal potential or zero volts when the concrete deck was poured. However, the investigators agreed to continue to check the power system.

The next step was to take load and source current measurements at the nearby capacitor bank. If the current-limiting fuse were open, then the circuit current would be unbalanced. The results are shown in Table 1. The current readings indicate that the capacitor bank was energized and that the circuit current was balanced across all three phases.

Table 1: Measurements Taken at Various Points in the Circuit

The next step was to take current readings and neutral-to-earth voltage (NEV) measurements on the circuit. The increasing and decreasing magnitude of the NEV values indicate that the shocking voltage was related to an open system neutral. The NEV decreased at poles where a CATV line was present. The line section from section B to section C did not have a CATV line. The NEV was related to the voltage drop in the system neutral without the CATV line.

Solutions

The owner has not experienced a shocking voltage since the concrete deck was poured. The NEV was reduced when the CATV line was extended around the cove to new homes. An alternate solution is to increase the system neutral size to reduce the neutral voltage drop.