Swimming Pool Ladder Shocking

Belton, North Carolina, USA

Background

The owner of a home was concerned about a shocking sensation that he felt as he used the ladder to get out of his swimming pool. The swimming pool had a concrete deck and a concrete shell instead of a vinyl liner.

Possible Causes

The initial investigation considered several possibilities:

• Faulty wiring on the owner's side.
• Overhead system neutral was open or damaged.

Action Taken

The possible causes were ruled out by:

• Temporarily de-energizing the owner's wiring by pulling the power meter.
• 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 2.0 VAC, with a high DC voltage. The pool's ladder and concrete deck were not bonded. The owner was informed of the lack of bonding at the pool's ladder and concrete deck.

The next step was to take current readings and neutral-to-earth voltage (NEV) measurements on the circuit. The decreasing NEV values indicate that the shocking voltage is related to the load on the single-phase line.

The next step was to drop the load at various sections along the line. The results are shown in Table 1. The current readings and NEV measurements indicate that the shocking voltage is a function of load on the long single-phase line.

Table 1: Measurements Taken at Various Points on the Circuit

The DC voltage value did not change when the load was dropped. The source of DC voltage appears not to be associated with the local transmission/pipeline companies. The high DC voltage value of 0.1 VDC appeared to be natural in the area compared to other areas.

The owner was getting shocked by both the NEV and the DC voltage. The NEV was riding on the top of the DC voltage, as evidenced by an oscilloscope measurement. The DC voltage was not entering the pool via the underwater light system. The neutral and ground wires of the pool light were disconnected from the pool. The concrete-lined pool was intercepting the naturally occurring DC voltage in the soil.

Solutions

The solution was to convert the 2400-volt line to 7200 volts and to improve the grounding because the shocking voltage was widespread. The primary and neutral current and the NEV would be reduced by 300% by converting the line to 7200 volts. The DC voltage should be reviewed after the line is converted to 7200 volts to see whether the owner can feel the low NEV and DC component.