What is this small voltage between spa water and natural earth ground?

[GM-237]

I've noticed a strange voltage reading between the water in my spa and natural earth ground. The reading varies between .35VAC and .7VAC. My wife noticed a small shock from the water after inserting her finger in the spa while standing outside the spa.

I tested the GFCI and it is working properly. The strange thing is that the voltage is still present after shutting off the breaker to the spa, as well as shutting off the main house breaker. With the power shut-off to the entire house, and there's no other power source anywhere in my yard, I'm assuming I'm picking up stray voltage from buried lines or possibly the neighbor's home?

The voltage reading is 0VAC when reading from the spa water to ground bar at the main spa panel. But, from the main panel ground bar to natural earth also reads between .35VAC and .7VAC.

Thoughts?

 

[Lucien Nunes]

0.7V is unlikely to give a shock. When wet and making good contact it is possible to detect quite low voltages but that seems remarkably low.

Regardless of whether your spa or house panel is powered on or off, there can be a voltage difference between the different points along the neutral wire of the supply, due to the voltage drop along the conductor when other consumers are using current. This causes a voltage difference between the various points at which is bonded to ground and to equipment grounding conductors, and hence between a circuit ground and 'real' ground.

I am sure someone will be along soon with some information on what the NEC says about spa grounding.