Got a call for a outdoor hot tub shocking some people yesterday. When I arrived at almost dark I got a voltage reading of around 20-30 volts from the water in hot tub to any ground source. I disconnected and returned today, reconnected and I cannot duplicate the reading. Matter of fact all seems fine. Tub fed with 2 pole 60 gfi breaker. There is 3 #6 conductors and a #8 ground to hot tub, however this hot tub did not have a neutral connection and diagram showed only a 3 wire connection. Thus the neutral was just capped in control box. I know a 2 pole GFI does not have to have a neutral to work, just trying to give details about installation. The breaker was installed correctly and test button trips it. I did find that the ground had a somewhat loose connection. I completely disconnected ground to see if I could duplicate and could not. Also 1 pole of the 2 pole GFI breaker hot wire was possibly loose, my helper checked that and said he got a good 2-3 turns on that. Any advice on how to proceed with trouble shooting. With out being able to duplicate the readings I got yesterday I am not sure what could have been causing this. Another note is this spa is on a dock over salt water. The conduit feeding and the spa is high above water line. We have troubleshot in the past transient voltage issues at close docks to this one and found corroded grounded conductors on both PC side and client side, but these issues were always with boat lifts actually in the salt water. Also have checked all ground connections and appear good. I have scheduled PC to put beast on meter next week as this always seems to highlight any problems! Thanks for any advice!
I don't have any revelation for you, but some troubleshooting steps that may help. Not necessarily in the order I have listed them.
When you checked "to any ground source" was that just to things that you knew were part of an equipotential or ground system or did you include a screwdriver in the earth?
One possibility is that what was energized somehow was the ground electrode system. A fault current of only one amp from anywhere in the system (not on a GFI) to a 25 ohm ground resistance would give you 25 volts on the whole grounding system.
How is the water in the tub itself grounded? Is the pump chamber itself (not just the motor) or some part of the circulating piping metal and grounded? If not, is there a ground plate in the tub?
A second possibility is that the water is what was energized. It would not take a lot of current leakage from something not GFCI protected to cause a pretty high voltage in the water if there is no effective grounding of the water.
You may not be able to duplicate what energized the water, but you could improve or completely fix the situation by making sure the water is grounded.
Finally did the people actually in the tub complain of a shock or just people getting in and out or touching someone outside the tub?
If people in the tub noticed it, there would have to be a voltage gradient in the water. Current flowing in at one point and going to ground at another.
If it was only people getting in and out, what is the surface around the tub and is it capable of being grounded effectively to the main grounding system like the pump, etc.?
Figuring out where the potential difference was located may help you track down the source. It may be that it was just a minor current leakage somewhere and proper bonding is all that it will take to correct things. The loose ground is suspicious, but it may only have been the factor that allowed a voltage to develop, and by itself disconnecting it would not replicate the situation.
Where was water splashed or dripping around the tub when you arrived? Could any of the water have gotten to an unsealed electrical source somewhere in the area? Under the tub deck? Try hosing the whole area down and waiting 30 minutes or more when trying to replicate.
And finally, how long had they been using the tub before they first noticed the shocks? Was there any electrical equipment like dock lighting that was on at night but not when you tried to replicate?
Good luck!
