Swimming Pool Handrail Shocking

Marion, North Carolina, USA

Background

The owner of a home was concerned about a shocking sensation that he and his family felt as they used the handrail to get out of their swimming pool. The owner's young children were very sensitive to the shocking voltage.

The owner inquired about the shocking voltage for the past several years. The initial investigation considered several possibilities:

• Faulty wiring on the customer side.
• Open or damaged underground primary cable neutral.
• Open or damaged overhead system neutral.

Action Taken

All of the identified possibilities were ruled out by:

• Temporarily de-energizing the owner's wiring by pulling the power meter.
• Inspecting the underground primary neutral with radar.
• Inspecting the system neutral because the area where the house is located is subject to ice storms and 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 3.7 VAC. The swimming pool's handrail was not bonded. The owner was informed of the lack of bonding at the swimming pool's handrail.

The next step in the investigation was to measure the neutral-to-earth voltage (NEV) along the underground line at the pad-mounted transformers. The NEV measurements decreased from the end of the single-phase underground line to the termination pole.

Normally, the decreasing NEV values indicate that the shocking voltage is related to the load. However, the load on the underground single-phase line was very low. Therefore, the next step in the investigation was to drop the load at the termination pole. The shocking voltage at the owner's swimming pool did not drop to zero.

The next step was to take current readings and NEV measurements on the circuit. The results are shown in Table 1. The current readings at the owner's location indicated that the chocking voltage was a function of current exiting the underground cable because the neutral return current was greater than the primary current. The neutral return current at the home was the sum of 2.1 amps for the neutral, 3.1 amps for the phone system, and 1.5 amps for the CATV. The total value for the return current was 6.7 amps. Current readings upstream at the three-phase power line indicated that the three phases were not balanced.

Solution

The solution to the owner's shocking voltage was o bond the handrail and to find the source of extra neutral return current. The source of the extra neutral return current appeared to be the imbalance of the three-phase line and possibly the REA circuits across the river from the customer.