Shocking at Swimming Pool Steps

Gaffney, South Carolina, USA

Background

A homeowner was concerned about a shocking sensation that he received when he got out of his swimming pool using the pool's underwater steps. The pool had a concrete deck but now handrail.

The local electric utility company believed that the owner's shocking voltage was related to a nearby transmission line. The transmission line was located about 1/2 mile from the owner's swimming pool.

Possible Causes

The initial investigation considered several possibilities:

• Faulty wiring on the owner's side.
• Open or damaged system neutral.

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 to 8.0 VAC from the pool's water to the concrete deck near the underwater steps. The swimming pool's concrete deck near the underwater steps was not bonded. The owner was informed of the lack of bonding for the deck.

The next step was to measure the neutral-to-earth voltage (NEV) along the circuit. The owner was located at the end of a long single-phase 2400-volt line. The NEV measurements were decreasing in value from the owner's transformer to the three-phase line.

The next step was to take current readings on the circuit. The decreasing NEV values indicated that the shocking voltage is related to the load. The current load on the overhead single-phase line was 29 amps. The three-phase load currents were 37.5, 0.1, and 13.6 for phases X, Y, and Z.

The next step was to drop the load on the owner's single-phase tap. The NEV went from 9.5 to 2.1 VAC. Therefore, the shocking voltage was related to the load on the single-phase tap and the unbalance on the three-phase line.

Solutions

The solution to the customer's shocking voltage was to bond the swimming pool's concrete deck near the underwater steps. Also, the long single-phase line should be converted from 2400 volts to 7200 volts.