Why am I getting an electric shock from the water in my hot tub?

Question

I have noticed that when I touch the water of my Hot Tub when I am grounded (barefoot standing outside of tub) I am getting a very small electric shock. Using a multimeter it is reading 2Vac between the water and the ground outside.

I have an RCD on both my ring main and a dedicated RCD on the Hot Tub, none of which trip.

Now the odd thing is that even with the socket switched off (but still plugged in) it still reads 2Vac. If I unplug the socket it reads 0Vac.

How is it reading 2Vac with only neural and earth wires connected?

Answer 1

Edit: This is sounding more and more like a problem with either a neighbor's electrical or the utility's supply. See last entry.

DON'T get in that hot tub again!

The "very small" shock was due to high impedance between you and the current. Impedance is extremely luck-based. Someone getting out of the pool might splash water where it had not been before, now the impedance is much lower and that "small" shock puts you in a wheelchair.

Hot tub miswiring is so common it's legendary. RCDs do not protect you from all wiring errors.

Don't get in the hot tub again until you positively find the cause and remove it.

8ma vs 30ma protection

RCDs also do not protect you from shock, necessarily. In Europe, RCDs have been used for a long time, and for a different reason - protecting houses from fires, not protecting humans from shock. Also, since they use whole-house RCDs, they must use a higher (more permissive) threshold, otherwise small leaks from many appliances will "stack" to cause nuisance trips. So whole-house protection is typically 30ma threshold.

Whereas in the US, GFCI is specifically for human safety, and it is 6ma or 8ma. This is too sensitive for a whole house, so it is applied circuit by circuit on circuits where it is helpful. (near sinks).

Your whole-house RCD would need to be 30ma, which is not enough for life-safety protection. It's less likely to outright kill you, but it's plenty enough to stun you - and when you are in water, being stunned means drowning.

Your hot tub should indeed have its own RCD, at the 6-8ma sensitivity level. However if you walk into a store and buy any random RCD, it's quite possible you'll find yourself holding a 30ma one. Perhaps your hot tub installer did exactly that.

RCDs do fail

I.E. they stop properly detecting ground faults. That's why the device has a "TEST" button. Use it.

It may be miswired to bypass the RCD

In fact, this is likely if the hot tub installer hit a situation where the RCD tripped when he hooked it up correctly. The RCD would trip when hooked up correctly, if the hot tub had a ground fault. Typical installer move is to jury-rig it any method that will work, then get paid.

This can also happen with amateur installers. They typically refuse to learn how to do the job properly (because that takes time learning about subjects they just don't care about), and simply "try random combinations" until one works. Many will work and also kill you. This might be one of those.

If the hot tub has a ground fault, fix it - seriously

Sometimes RCDs trip because the downline device is connected correctly, but actually does have a ground fault. This tends to surprise the heck out of people, they are in full disbelief -- "MY appliance has a ground fault? This cannot be!" (even they know nothing about ground faults).

I've seen people replace RCDs twice simply because they cannot believe they actually have a ground fault. And of course they feel totally justified in bypassing safety protection altogether.

So don't be in denial about that. There is a real possibility that the hot tub has a ground fault. If so, fix it.

It might not even be the hot tub

There's an outside chance this shock is entirely unrelated to the hot tub. It's possible the dangerous voltage is being sourced from some other thing in your yard, and the hot tub is correctly providing grounding, thus completing the circuit. If so, the cure is a thorough search of your house's electrical system for any defects. And if neighbors are close, you may need to bring out someone to test for problems coming from them.

In any case, this is nothing to trifle with.

Answer 2

I had an electrician to check out the problem and:

1. I am in the UK and there is only live and neutral at the meter (earth and neutral are the same wire at that point)
2. The Hot Tub water is directly conncted to Earth
3. The mains electrics in my property all checked out fine, incoming supply fine.
4. No faults with the Hob Tub
5. RCD's tested and working
6. He is surpirsed I can even feel 2Vac, he could not feel it.

So it's still a bit of a mystery, but if I stand near the Hot Tub (off and unpluggedd) and measure voltage between the ground (the actual soil) and the Earth wire, it reads 5Vac, no current. If I switch off ALL power (break live and neutral) at the meter I still get the 5Vac Anyway, the Hot Tub is safe to use.

Answer 3

Now the odd thing is that even with the socket switched off (but still plugged in) it still reads 2Vac. If I unplug the socket it reads 0Vac.

How is it reading 2Vac with only neural and earth wires connected?

By ground wire not being at 0Vac.

Typically this would be caused by problems elsewhere in your home, such as an appliance drawing high amount of current and your ground rod making poor contact with the ground. It could also be poor connections in the ground wires themselves.

If you want to test it yourself, you can do the ground voltage measurements from various outlets and also turn appliances on/off. If your house has all the grounds connected together well, they'll probably all read the same voltage. In that case, the problem is likely with the central grounding rod.

Answer 4

Its an inherent fault that's apparent on our UK TNCS supply type. Our earth (your hot tubs earth and its water) is always at the same protentional as your neutral, which is nearly always above Zero. You access this via the water in the tub and touch true earth (zero volts) via wet grass a you will get a shock IMO they should not be installed using this system ...period

Answer 5

I got an electric shock whilst in a Lay-Z-Spa Vegas.

It was leaking from the thermostat housing, with water leaking and dripping on the heater causing a short to travel through the water pipe.

I took the top of the thermostat housing and found the square rubber seal split. I used silicone caulk to repair the seal and refitted it.

No more leaks, no more shocks. Happy spa days!

Answer 6

I now use foam mats underneath and all around the hot tub to mitigate the risk of an earth fault. In fact my neighbour had a fault on the incoming cable (under her garden) which caused a small fire in an applicance, scottish power were all over it, never seen so many turn up at once. TNCS is just a bad idea to save money on copper.

Answer 7

I am actually experiencing same thing right now. it has been tested by electricians to confirm. i am getting 3.5-4v ac from earth ground to hottub water even with my main disconnect at meter off. same v measure from earth ground to steel siding. hydro will be doing some testing feb 2/22 but they said if its under 10v then that is within the standards and nothing will be done it is just how their system works. location ontario canada - Getting voltage readings from a hottub doesnt always mean its coming from the hottub. I have put rubber mats all around the tub to ensure no shock from situation happening.

Answer 8

I experienced the same problem. Our jacuzzi is standing on artificial grass. So when the pump of the jacuzzi is working , the jacuzzi generates some electrical current in the water. Just like a car that is generatong current from headwind. When you get out of the car you get a electric shock. The current in the water is very small but accumulates. If the jacuzzi is not grounded the current becomes stronger and you can feel small shocks when you are standing barefoot near the jacuzzi and touch the water. So the grounding of your wall socket will prevent build up of static current caused by pump flow / static generation.